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| author | Daniel Mack <daniel@zonque.org> | 2014-09-11 21:50:47 +0200 |
|---|---|---|
| committer | Maciej Wereski <m.wereski@partner.samsung.com> | 2015-06-09 11:31:20 +0200 |
| commit | 81329ae69f17632f7acab21630f8a0cb1bea1b5b (patch) | |
| tree | c14bc4eecd5166f64eb109c62979ec62b814e6eb | |
| parent | d1866567499505b9f142f3073e95287db6cf36c2 (diff) | |
| download | linux-3.10-81329ae69f17632f7acab21630f8a0cb1bea1b5b.tar.gz linux-3.10-81329ae69f17632f7acab21630f8a0cb1bea1b5b.tar.bz2 linux-3.10-81329ae69f17632f7acab21630f8a0cb1bea1b5b.zip | |
kdbus: add documentation
kdbus is a system for low-latency, low-overhead, easy to use
interprocess communication (IPC).
The interface to all functions in this driver is implemented via ioctls
on files exposed through a filesystem called 'kdbusfs'. The default
mount point of kdbusfs is /sys/fs/kdbus. This patch adds detailed
documentation about the kernel level API design.
This patch adds a set of comprehensive set of DocBook files which
can be turned into man-pages using 'make mandocs', or into HTML
files with 'make htmldocs'.
Change-Id: Ic99ed66f2e2879b9664f21ed653240b2ebdc6204
Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | Documentation/Makefile | 2 | ||||
| -rw-r--r-- | Documentation/kdbus/Makefile | 30 | ||||
| -rw-r--r-- | Documentation/kdbus/kdbus.bus.xml | 360 | ||||
| -rw-r--r-- | Documentation/kdbus/kdbus.connection.xml | 1252 | ||||
| -rw-r--r-- | Documentation/kdbus/kdbus.endpoint.xml | 436 | ||||
| -rw-r--r-- | Documentation/kdbus/kdbus.fs.xml | 124 | ||||
| -rw-r--r-- | Documentation/kdbus/kdbus.item.xml | 840 | ||||
| -rw-r--r-- | Documentation/kdbus/kdbus.match.xml | 553 | ||||
| -rw-r--r-- | Documentation/kdbus/kdbus.message.xml | 1277 | ||||
| -rw-r--r-- | Documentation/kdbus/kdbus.name.xml | 711 | ||||
| -rw-r--r-- | Documentation/kdbus/kdbus.policy.xml | 406 | ||||
| -rw-r--r-- | Documentation/kdbus/kdbus.pool.xml | 320 | ||||
| -rw-r--r-- | Documentation/kdbus/kdbus.xml | 1012 | ||||
| -rw-r--r-- | Documentation/kdbus/stylesheet.xsl | 16 | ||||
| -rw-r--r-- | Makefile | 1 |
15 files changed, 7339 insertions, 1 deletions
diff --git a/Documentation/Makefile b/Documentation/Makefile index 31d302bc586..b87da55951d 100644 --- a/Documentation/Makefile +++ b/Documentation/Makefile @@ -1,3 +1,3 @@ obj-m := DocBook/ accounting/ auxdisplay/ connector/ \ - filesystems/ filesystems/configfs/ ia64/ laptops/ networking/ \ + filesystems/ filesystems/configfs/ ia64/ kdbus/ laptops/ networking/ \ pcmcia/ spi/ timers/ watchdog/src/ misc-devices/mei/ diff --git a/Documentation/kdbus/Makefile b/Documentation/kdbus/Makefile new file mode 100644 index 00000000000..cd6b48ee41b --- /dev/null +++ b/Documentation/kdbus/Makefile @@ -0,0 +1,30 @@ +DOCS := \ + kdbus.xml \ + kdbus.bus.xml \ + kdbus.connection.xml \ + kdbus.endpoint.xml \ + kdbus.fs.xml \ + kdbus.item.xml \ + kdbus.match.xml \ + kdbus.message.xml \ + kdbus.name.xml \ + kdbus.policy.xml \ + kdbus.pool.xml + +XMLFILES := $(addprefix $(obj)/,$(DOCS)) +MANFILES := $(patsubst %.xml, %.7, $(XMLFILES)) +HTMLFILES := $(patsubst %.xml, %.html, $(XMLFILES)) + +XMLTO_ARGS := -m $(obj)/stylesheet.xsl + +%.7: %.xml + xmlto man $(XMLTO_ARGS) -o . $< + +%.html: %.xml + xmlto html-nochunks $(XMLTO_ARGS) -o . $< + +mandocs: $(MANFILES) + +htmldocs: $(HTMLFILES) + +clean-files := $(MANFILES) $(HTMLFILES) diff --git a/Documentation/kdbus/kdbus.bus.xml b/Documentation/kdbus/kdbus.bus.xml new file mode 100644 index 00000000000..4d875e59ac0 --- /dev/null +++ b/Documentation/kdbus/kdbus.bus.xml @@ -0,0 +1,360 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus.bus"> + + <refentryinfo> + <title>kdbus.bus</title> + <productname>kdbus.bus</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus.bus</refname> + <refpurpose>kdbus bus</refpurpose> + </refnamediv> + + <refsect1> + <title>Description</title> + + <para> + A bus is a resource that is shared between connections in order to + transmit messages (see + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + ). + Each bus is independent, and operations on the bus will not have any + effect on other buses. A bus is a management entity that controls the + addresses of its connections, their policies and message transactions + performed via this bus. + </para> + <para> + Each bus is bound to the mount instance it was created on. It has a + custom name that is unique across all buses of a domain. In + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + , a bus is presented as a directory. No operations can be performed on + the bus itself; instead you need to perform the operations on an endpoint + associated with the bus. Endpoints are accessible as files underneath the + bus directory. A default endpoint called <constant>bus</constant> is + provided on each bus. + </para> + <para> + Bus names may be chosen freely except for one restriction: the name must + be prefixed with the numeric effective UID of the creator and a dash. This + is required to avoid namespace clashes between different users. When + creating a bus, the name that is passed in must be properly formatted, or + the kernel will refuse creation of the bus. Example: + <literal>1047-foobar</literal> is an acceptable name for a bus + registered by a user with UID 1047. However, + <literal>1024-foobar</literal> is not, and neither is + <literal>foobar</literal>. The UID must be provided in the + user-namespace of the bus owner. + </para> + <para> + To create a new bus, you need to open the control file of a domain and + employ the <constant>KDBUS_CMD_BUS_MAKE</constant> ioctl. The control + file descriptor that was used to issue + <constant>KDBUS_CMD_BUS_MAKE</constant> must not previously have been + used for any other control-ioctl and must be kept open for the entire + life-time of the created bus. Closing it will immediately cleanup the + entire bus and all its associated resources and endpoints. Every control + file descriptor can only be used to create a single new bus; from that + point on, it is not used for any further communication until the final + <citerefentry> + <refentrytitle>close</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + . + </para> + <para> + Each bus will generate a random, 128-bit UUID upon creation. This UUID + will be returned to creators of connections through + <varname>kdbus_cmd_hello.id128</varname> and can be used to uniquely + identify buses, even across different machines or containers. The UUID + will have its variant bits set to <literal>DCE</literal>, and denote + version 4 (random). For more details on UUIDs, see <ulink + url="https://en.wikipedia.org/wiki/Universally_unique_identifier"> + the Wikipedia article on UUIDs</ulink>. + </para> + + </refsect1> + + <refsect1> + <title>Creating buses</title> + <para> + To create a new bus, the <constant>KDBUS_CMD_BUS_MAKE</constant> + command is used. It takes a <type>struct kdbus_cmd</type> argument. + </para> + <programlisting> +struct kdbus_cmd { + __u64 size; + __u64 flags; + __u64 return_flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para>The flags for creation.</para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_MAKE_ACCESS_GROUP</constant></term> + <listitem> + <para>Make the bus file group-accessible.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_MAKE_ACCESS_WORLD</constant></term> + <listitem> + <para>Make the bus file world-accessible.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_FLAG_NEGOTIATE</constant></term> + <listitem> + <para> + Requests a set of valid flags for this ioctl. When this bit is + set, no action is taken; the ioctl will return + <errorcode>0</errorcode>, and the <varname>flags</varname> + field will have all bits set that are valid for this command. + The <constant>KDBUS_FLAG_NEGOTIATE</constant> bit will be + cleared by the operation. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + The following items (see + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + ) are expected for <constant>KDBUS_CMD_BUS_MAKE</constant>. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_MAKE_NAME</constant></term> + <listitem> + <para> + Contains a null-terminated string that identifies the + bus. The name must be unique across the kdbus domain and + must start with the effective UID of the caller, followed by + a '<literal>-</literal>' (dash). This item is mandatory. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_BLOOM_PARAMETER</constant></term> + <listitem> + <para> + Bus-wide bloom parameters passed in a + <type>struct kdbus_bloom_parameter</type>. These settings are + copied back to new connections verbatim. This item is + mandatory. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for a more detailed description of this item. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_ATTACH_FLAGS_RECV</constant></term> + <listitem> + <para> + An optional item that contains a set of required attach flags + that connections must allow. This item is used as a + negotiation measure during connection creation. If connections + do not satisfy the bus requirements, they are not allowed on + the bus. If not set, the bus does not require any metadata to + be attached; in this case connections are free to set their + own attach flags. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_ATTACH_FLAGS_SEND</constant></term> + <listitem> + <para> + An optional item that contains a set of attach flags that are + returned to connections when they query the bus creator + metadata. If not set, no metadata is returned. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NEGOTIATE</constant></term> + <listitem><para> + With this item, programs can <emphasis>probe</emphasis> the + kernel for known item types. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para></listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + </variablelist> + + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <constant>EINVAL</constant>. + </para> + </refsect1> + + <refsect1> + <title>Return value</title> + <para> + On success, all mentioned ioctl commands return <errorcode>0</errorcode>; + on error, <errorcode>-1</errorcode> is returned, and + <varname>errno</varname> is set to indicate the error. + If the issued ioctl is illegal for the file descriptor used, + <varname>errno</varname> will be set to <constant>ENOTTY</constant>. + </para> + + <refsect2> + <title> + <constant>KDBUS_CMD_BUS_MAKE</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EBADMSG</constant></term> + <listitem><para> + A mandatory item is missing. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + The flags supplied in the <constant>struct kdbus_cmd</constant> + are invalid or the supplied name does not start with the current + UID and a '<literal>-</literal>' (dash). + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EEXIST</constant></term> + <listitem><para> + A bus of that name already exists. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ESHUTDOWN</constant></term> + <listitem><para> + The kdbus mount instance for the bus was already shut down. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EMFILE</constant></term> + <listitem><para> + The maximum number of buses for the current user is exhausted. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + </simplelist> + </refsect1> +</refentry> diff --git a/Documentation/kdbus/kdbus.connection.xml b/Documentation/kdbus/kdbus.connection.xml new file mode 100644 index 00000000000..09852125b2d --- /dev/null +++ b/Documentation/kdbus/kdbus.connection.xml @@ -0,0 +1,1252 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus.connection"> + + <refentryinfo> + <title>kdbus.connection</title> + <productname>kdbus.connection</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus.connection</refname> + <refpurpose>kdbus connection</refpurpose> + </refnamediv> + + <refsect1> + <title>Description</title> + + <para> + Connections are identified by their <emphasis>connection ID</emphasis>, + internally implemented as a <type>uint64_t</type> counter. + The IDs of every newly created bus start at <constant>1</constant>, and + every new connection will increment the counter by <constant>1</constant>. + The IDs are not reused. + </para> + <para> + In higher level tools, the user visible representation of a connection is + defined by the D-Bus protocol specification as + <constant>":1.<ID>"</constant>. + </para> + <para> + Messages with a specific <type>uint64_t</type> destination ID are + directly delivered to the connection with the corresponding ID. Signal + messages (see + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>) + may be addressed to the special destination ID + <constant>KDBUS_DST_ID_BROADCAST</constant> (~0ULL) and will then + potentially be delivered to all currently active connections on the bus. + However, in order to receive any signal messages, clients must subscribe + to them by installing a match (see + <citerefentry> + <refentrytitle>kdbus.match</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + ). + </para> + <para> + Messages synthesized and sent directly by the kernel will carry the + special source ID <constant>KDBUS_SRC_ID_KERNEL</constant> (0). + </para> + <para> + In addition to the unique <type>uint64_t</type> connection ID, + established connections can request the ownership of + <emphasis>well-known names</emphasis>, under which they can be found and + addressed by other bus clients. A well-known name is associated with one + and only one connection at a time. See + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + on name acquisition, the name registry, and the validity of names. + </para> + <para> + Messages can specify the special destination ID + <constant>KDBUS_DST_ID_NAME</constant> (0) and carry a well-known name + in the message data. Such a message is delivered to the destination + connection which owns that well-known name. + </para> + + <programlisting><![CDATA[ + +-------------------------------------------------------------------------+ + | +---------------+ +---------------------------+ | + | | Connection | | Message | -----------------+ | + | | :1.22 | --> | src: 22 | | | + | | | | dst: 25 | | | + | | | | | | | + | | | | | | | + | | | +---------------------------+ | | + | | | | | + | | | <--------------------------------------+ | | + | +---------------+ | | | + | | | | + | +---------------+ +---------------------------+ | | | + | | Connection | | Message | -----+ | | + | | :1.25 | --> | src: 25 | | | + | | | | dst: 0xffffffffffffffff | -------------+ | | + | | | | (KDBUS_DST_ID_BROADCAST) | | | | + | | | | | ---------+ | | | + | | | +---------------------------+ | | | | + | | | | | | | + | | | <--------------------------------------------------+ | + | +---------------+ | | | + | | | | + | +---------------+ +---------------------------+ | | | + | | Connection | | Message | --+ | | | + | | :1.55 | --> | src: 55 | | | | | + | | | | dst: 0 / org.foo.bar | | | | | + | | | | | | | | | + | | | | | | | | | + | | | +---------------------------+ | | | | + | | | | | | | + | | | <------------------------------------------+ | | + | +---------------+ | | | + | | | | + | +---------------+ | | | + | | Connection | | | | + | | :1.81 | | | | + | | org.foo.bar | | | | + | | | | | | + | | | | | | + | | | <-----------------------------------+ | | + | | | | | + | | | <----------------------------------------------+ | + | +---------------+ | + +-------------------------------------------------------------------------+ + ]]></programlisting> + </refsect1> + + <refsect1> + <title>Privileged connections</title> + <para> + A connection is considered <emphasis>privileged</emphasis> if the user + it was created by is the same that created the bus, or if the creating + task had <constant>CAP_IPC_OWNER</constant> set when it called + <constant>KDBUS_CMD_HELLO</constant> (see below). + </para> + <para> + Privileged connections have permission to employ certain restricted + functions and commands, which are explained below and in other kdbus + man-pages. + </para> + </refsect1> + + <refsect1> + <title>Activator and policy holder connection</title> + <para> + An <emphasis>activator</emphasis> connection is a placeholder for a + <emphasis>well-known name</emphasis>. Messages sent to such a connection + can be used to start an implementer connection, which will then get all + the messages from the activator copied over. An activator connection + cannot be used to send any message. + </para> + <para> + A <emphasis>policy holder</emphasis> connection only installs a policy + for one or more names. These policy entries are kept active as long as + the connection is alive, and are removed once it terminates. Such a + policy connection type can be used to deploy restrictions for names that + are not yet active on the bus. A policy holder connection cannot be used + to send any message. + </para> + <para> + The creation of activator or policy holder connections is restricted to + privileged users on the bus (see above). + </para> + </refsect1> + + <refsect1> + <title>Monitor connections</title> + <para> + Monitors are eavesdropping connections that receive all the traffic on the + bus, but is invisible to other connections. Such connections have all + properties of any other, regular connection, except for the following + details: + </para> + + <itemizedlist> + <listitem><para> + They will get every message sent over the bus, both unicasts and + broadcasts. + </para></listitem> + + <listitem><para> + Installing matches for signal messages is neither necessary + nor allowed. + </para></listitem> + + <listitem><para> + They cannot send messages or be directly addressed as receiver. + </para></listitem> + + <listitem><para> + They cannot own well-known names. Therefore, they also can't operate as + activators. + </para></listitem> + + <listitem><para> + Their creation and destruction will not cause + <constant>KDBUS_ITEM_ID_{ADD,REMOVE}</constant> (see + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>). + </para></listitem> + + <listitem><para> + They are not listed with their unique name in name registry dumps + (see <constant>KDBUS_CMD_NAME_LIST</constant> in + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>), so other connections cannot detect the presence of + a monitor. + </para></listitem> + </itemizedlist> + <para> + The creation of monitor connections is restricted to privileged users on + the bus (see above). + </para> + </refsect1> + + <refsect1> + <title>Creating connections</title> + <para> + A connection to a bus is created by opening an endpoint file (see + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>) + of a bus and becoming an active client with the + <constant>KDBUS_CMD_HELLO</constant> ioctl. Every connection has a unique + identifier on the bus and can address messages to every other connection + on the same bus by using the peer's connection ID as the destination. + </para> + <para> + The <constant>KDBUS_CMD_HELLO</constant> ioctl takes a <type>struct + kdbus_cmd_hello</type> as argument. + </para> + + <programlisting> +struct kdbus_cmd_hello { + __u64 size; + __u64 flags; + __u64 return_flags; + __u64 attach_flags_send; + __u64 attach_flags_recv; + __u64 bus_flags; + __u64 id; + __u64 pool_size; + __u64 offset; + __u8 id128[16]; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem> + <para>Flags to apply to this connection</para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_HELLO_ACCEPT_FD</constant></term> + <listitem> + <para> + When this flag is set, the connection can be sent file + descriptors as message payload of unicast messages. If it's + not set, an attempt to send file descriptors will result in + <constant>-ECOMM</constant> on the sender's side. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_HELLO_ACTIVATOR</constant></term> + <listitem> + <para> + Make this connection an activator (see above). With this bit + set, an item of type <constant>KDBUS_ITEM_NAME</constant> has + to be attached. This item describes the well-known name this + connection should be an activator for. + A connection can not be an activator and a policy holder at + the same time time, so this bit is not allowed together with + <constant>KDBUS_HELLO_POLICY_HOLDER</constant>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_HELLO_POLICY_HOLDER</constant></term> + <listitem> + <para> + Make this connection a policy holder (see above). With this + bit set, an item of type <constant>KDBUS_ITEM_NAME</constant> + has to be attached. This item describes the well-known name + this connection should hold a policy for. + A connection can not be an activator and a policy holder at + the same time time, so this bit is not allowed together with + <constant>KDBUS_HELLO_ACTIVATOR</constant>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_HELLO_MONITOR</constant></term> + <listitem> + <para> + Make this connection a monitor connection (see above). + </para> + <para> + This flag can only be set by privileged bus connections. See + below for more information. + A connection can not be monitor and an activator or a policy + holder at the same time time, so this bit is not allowed + together with <constant>KDBUS_HELLO_ACTIVATOR</constant> or + <constant>KDBUS_HELLO_POLICY_HOLDER</constant>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_FLAG_NEGOTIATE</constant></term> + <listitem> + <para> + Requests a set of valid flags for this ioctl. When this bit is + set, no action is taken; the ioctl will return + <errorcode>0</errorcode>, and the <varname>flags</varname> + field will have all bits set that are valid for this command. + The <constant>KDBUS_FLAG_NEGOTIATE</constant> bit will be + cleared by the operation. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>attach_flags_send</varname></term> + <listitem><para> + Set the bits for metadata this connection permits to be sent to the + receiving peer. Only metadata items that are both allowed to be sent + by the sender and that are requested by the receiver will be attached + to the message. Note, however, that the bus may optionally require + some of those bits to be set. If the match fails, the ioctl will fail + with <varname>errno</varname> set to + <constant>ECONNREFUSED</constant>. In either case, when returning the + field will be set to the mask of metadata items that are enforced by + the bus with the <constant>KDBUS_FLAGS_KERNEL</constant> bit set as + well. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>attach_flags_recv</varname></term> + <listitem><para> + Request the attachment of metadata for each message received by this + connection. See + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for information about metadata, and + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + regarding items in general. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>bus_flags</varname></term> + <listitem><para> + Upon successful completion of the ioctl, this member will contain the + flags of the bus it connected to. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>id</varname></term> + <listitem><para> + Upon successful completion of the command, this member will contain + the numerical ID of the new connection. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>pool_size</varname></term> + <listitem><para> + The size of the communication pool, in bytes. The pool can be + accessed by calling + <citerefentry> + <refentrytitle>mmap</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + on the file descriptor that was used to issue the + <constant>KDBUS_CMD_HELLO</constant> ioctl. + The pool size of a connection must be greater than + <constant>0</constant> and a multiple of + <constant>PAGE_SIZE</constant>. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>offset</varname></term> + <listitem><para> + The kernel will return the offset in the pool where returned details + will be stored. See below. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>id128</varname></term> + <listitem><para> + Upon successful completion of the ioctl, this member will contain the + <emphasis>128-bit UUID</emphasis> of the connected bus. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + Variable list of items containing optional additional information. + The following items are currently expected/valid: + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_CONN_DESCRIPTION</constant></term> + <listitem> + <para> + Contains a string that describes this connection, so it can + be identified later. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NAME</constant></term> + <term><constant>KDBUS_ITEM_POLICY_ACCESS</constant></term> + <listitem> + <para> + For activators and policy holders only, combinations of + these two items describe policy access entries. See + <citerefentry> + <refentrytitle>kdbus.policy</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for further details. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_CREDS</constant></term> + <term><constant>KDBUS_ITEM_PIDS</constant></term> + <term><constant>KDBUS_ITEM_SECLABEL</constant></term> + <listitem> + <para> + Privileged bus users may submit these types in order to + create connections with faked credentials. This information + will be returned when peer information is queried by + <constant>KDBUS_CMD_CONN_INFO</constant>. See below for more + information on retrieving information on connections. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NEGOTIATE</constant></term> + <listitem><para> + With this item, programs can <emphasis>probe</emphasis> the + kernel for known item types. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para></listitem> + </varlistentry> + </variablelist> + + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <constant>EINVAL</constant>. + </para> + </listitem> + </varlistentry> + </variablelist> + + <para> + At the offset returned in the <varname>offset</varname> field of + <type>struct kdbus_cmd_hello</type>, the kernel will store items + of the following types: + </para> + + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_BLOOM_PARAMETER</constant></term> + <listitem> + <para> + Bloom filter parameter as defined by the bus creator. + </para> + </listitem> + </varlistentry> + </variablelist> + + <para> + The offset in the pool has to be freed with the + <constant>KDBUS_CMD_FREE</constant> ioctl. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for further information. + </para> + </refsect1> + + <refsect1> + <title>Retrieving information on a connection</title> + <para> + The <constant>KDBUS_CMD_CONN_INFO</constant> ioctl can be used to + retrieve credentials and properties of the initial creator of a + connection. This ioctl uses the following struct. + </para> + + <programlisting> +struct kdbus_cmd_info { + __u64 size; + __u64 flags; + __u64 return_flags; + __u64 id; + __u64 attach_flags; + __u64 offset; + __u64 info_size; + struct kdbus_item items[0]; +}; + </programlisting> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para> + Currently, no flags are supported. + <constant>KDBUS_FLAG_NEGOTIATE</constant> is accepted to probe for + valid flags. If set, the ioctl will return <errorcode>0</errorcode>, + and the <varname>flags</varname> field is set to + <constant>0</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>id</varname></term> + <listitem><para> + The numerical ID of the connection for which information is to be + retrieved. If set to a non-zero value, the + <constant>KDBUS_ITEM_OWNED_NAME</constant> item is ignored. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para> + Specifies which metadata items should be attached to the answer. See + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>offset</varname></term> + <listitem><para> + When the ioctl returns, this field will contain the offset of the + connection information inside the caller's pool. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for further information. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>info_size</varname></term> + <listitem><para> + The kernel will return the size of the returned information, so + applications can optionally + <citerefentry> + <refentrytitle>mmap</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + specific parts of the pool. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for further information. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + The following items are expected for + <constant>KDBUS_CMD_CONN_INFO</constant>. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_OWNED_NAME</constant></term> + <listitem> + <para> + Contains the well-known name of the connection to look up as. + This item is mandatory if the <varname>id</varname> field is + set to 0. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NEGOTIATE</constant></term> + <listitem><para> + With this item, programs can <emphasis>probe</emphasis> the + kernel for known item types. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para></listitem> + </varlistentry> + </variablelist> + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <constant>EINVAL</constant>. + </para> + </listitem> + </varlistentry> + </variablelist> + + <para> + When the ioctl returns, the following struct will be stored in the + caller's pool at <varname>offset</varname>. The fields in this struct + are described below. + </para> + + <programlisting> +struct kdbus_info { + __u64 size; + __u64 id; + __u64 flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>id</varname></term> + <listitem><para> + The connection's unique ID. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para> + The connection's flags as specified when it was created. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + Depending on the <varname>flags</varname> field in + <type>struct kdbus_cmd_info</type>, items of types + <constant>KDBUS_ITEM_OWNED_NAME</constant> and + <constant>KDBUS_ITEM_CONN_DESCRIPTION</constant> may follow here. + <constant>KDBUS_ITEM_NEGOTIATE</constant> is also allowed. + </para> + </listitem> + </varlistentry> + </variablelist> + + <para> + Once the caller is finished with parsing the return buffer, it needs to + employ the <constant>KDBUS_CMD_FREE</constant> command for the offset, in + order to free the buffer part. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for further information. + </para> + </refsect1> + + <refsect1> + <title>Getting information about a connection's bus creator</title> + <para> + The <constant>KDBUS_CMD_BUS_CREATOR_INFO</constant> ioctl takes the same + struct as <constant>KDBUS_CMD_CONN_INFO</constant>, but is used to + retrieve information about the creator of the bus the connection is + attached to. The metadata returned by this call is collected during the + creation of the bus and is never altered afterwards, so it provides + pristine information on the task that created the bus, at the moment when + it did so. + </para> + <para> + In response to this call, a slice in the connection's pool is allocated + and filled with an object of type <type>struct kdbus_info</type>, + pointed to by the ioctl's <varname>offset</varname> field. + </para> + + <programlisting> +struct kdbus_info { + __u64 size; + __u64 id; + __u64 flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>id</varname></term> + <listitem><para> + The bus ID. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para> + The bus flags as specified when it was created. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + Metadata information is stored in items here. The item list + contains a <constant>KDBUS_ITEM_MAKE_NAME</constant> item that + indicates the bus name of the calling connection. + <constant>KDBUS_ITEM_NEGOTIATE</constant> is allowed to probe + for known item types. + </para> + </listitem> + </varlistentry> + </variablelist> + + <para> + Once the caller is finished with parsing the return buffer, it needs to + employ the <constant>KDBUS_CMD_FREE</constant> command for the offset, in + order to free the buffer part. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for further information. + </para> + </refsect1> + + <refsect1> + <title>Updating connection details</title> + <para> + Some of a connection's details can be updated with the + <constant>KDBUS_CMD_CONN_UPDATE</constant> ioctl, using the file + descriptor that was used to create the connection. The update command + uses the following struct. + </para> + + <programlisting> +struct kdbus_cmd { + __u64 size; + __u64 flags; + __u64 return_flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para> + Currently, no flags are supported. + <constant>KDBUS_FLAG_NEGOTIATE</constant> is accepted to probe for + valid flags. If set, the ioctl will return <errorcode>0</errorcode>, + and the <varname>flags</varname> field is set to + <constant>0</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + Items to describe the connection details to be updated. The + following item types are supported. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_ATTACH_FLAGS_SEND</constant></term> + <listitem> + <para> + Supply a new set of metadata items that this connection + permits to be sent along with messages. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_ATTACH_FLAGS_RECV</constant></term> + <listitem> + <para> + Supply a new set of metadata items that this connection + requests to be attached to each message. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NAME</constant></term> + <term><constant>KDBUS_ITEM_POLICY_ACCESS</constant></term> + <listitem> + <para> + Policy holder connections may supply a new set of policy + information with these items. For other connection types, + <constant>EOPNOTSUPP</constant> is returned in + <varname>errno</varname>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NEGOTIATE</constant></term> + <listitem><para> + With this item, programs can <emphasis>probe</emphasis> the + kernel for known item types. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para></listitem> + </varlistentry> + </variablelist> + + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <constant>EINVAL</constant>. + </para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Termination of connections</title> + <para> + A connection can be terminated by simply calling + <citerefentry> + <refentrytitle>close</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + on its file descriptor. All pending incoming messages will be discarded, + and the memory allocated by the pool will be freed. + </para> + + <para> + An alternative way of closing down a connection is via the + <constant>KDBUS_CMD_BYEBYE</constant> ioctl. This ioctl will succeed only + if the message queue of the connection is empty at the time of closing; + otherwise, the ioctl will fail with <varname>errno</varname> set to + <constant>EBUSY</constant>. When this ioctl returns + successfully, the connection has been terminated and won't accept any new + messages from remote peers. This way, a connection can be terminated + race-free, without losing any messages. The ioctl takes an argument of + type <type>struct kdbus_cmd</type>. + </para> + + <programlisting> +struct kdbus_cmd { + __u64 size; + __u64 flags; + __u64 return_flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para> + Currently, no flags are supported. + <constant>KDBUS_FLAG_NEGOTIATE</constant> is accepted to probe for + valid flags. If set, the ioctl will fail with + <varname>errno</varname> set to <constant>EPROTO</constant>, and + the <varname>flags</varname> field is set to <constant>0</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + Items to describe the connection details to be updated. The + following item types are supported. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_NEGOTIATE</constant></term> + <listitem><para> + With this item, programs can <emphasis>probe</emphasis> the + kernel for known item types. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para></listitem> + </varlistentry> + </variablelist> + + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <constant>EINVAL</constant>. + </para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Return value</title> + <para> + On success, all mentioned ioctl commands return <errorcode>0</errorcode>; + on error, <errorcode>-1</errorcode> is returned, and + <varname>errno</varname> is set to indicate the error. + If the issued ioctl is illegal for the file descriptor used, + <varname>errno</varname> will be set to <constant>ENOTTY</constant>. + </para> + + <refsect2> + <title> + <constant>KDBUS_CMD_HELLO</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EFAULT</constant></term> + <listitem><para> + The supplied pool size was 0 or not a multiple of the page size. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + The flags supplied in <type>struct kdbus_cmd_hello</type> + are invalid. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + An illegal combination of + <constant>KDBUS_HELLO_MONITOR</constant>, + <constant>KDBUS_HELLO_ACTIVATOR</constant> and + <constant>KDBUS_HELLO_POLICY_HOLDER</constant> was passed in + <varname>flags</varname>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + An invalid set of items was supplied. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ECONNREFUSED</constant></term> + <listitem><para> + The attach_flags_send field did not satisfy the requirements of + the bus. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EPERM</constant></term> + <listitem><para> + A <constant>KDBUS_ITEM_CREDS</constant> items was supplied, but the + current user is not privileged. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ESHUTDOWN</constant></term> + <listitem><para> + The bus you were trying to connect to has already been shut down. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EMFILE</constant></term> + <listitem><para> + The maximum number of connections on the bus has been reached. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EOPNOTSUPP</constant></term> + <listitem><para> + The endpoint does not support the connection flags supplied in + <type>struct kdbus_cmd_hello</type>. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title> + <constant>KDBUS_CMD_BYEBYE</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EALREADY</constant></term> + <listitem><para> + The connection has already been shut down. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EBUSY</constant></term> + <listitem><para> + There are still messages queued up in the connection's pool. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title> + <constant>KDBUS_CMD_CONN_INFO</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Invalid flags, or neither an ID nor a name was provided, or the + name is invalid. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ESRCH</constant></term> + <listitem><para> + Connection lookup by name failed. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ENXIO</constant></term> + <listitem><para> + No connection with the provided connection ID found. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title> + <constant>KDBUS_CMD_CONN_UPDATE</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Illegal flags or items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Wildcards submitted in policy entries, or illegal sequence + of policy items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EOPNOTSUPP</constant></term> + <listitem><para> + Operation not supported by connection. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>E2BIG</constant></term> + <listitem><para> + Too many policy items attached. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.policy</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + </simplelist> + </refsect1> +</refentry> diff --git a/Documentation/kdbus/kdbus.endpoint.xml b/Documentation/kdbus/kdbus.endpoint.xml new file mode 100644 index 00000000000..76e325d4e93 --- /dev/null +++ b/Documentation/kdbus/kdbus.endpoint.xml @@ -0,0 +1,436 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus.endpoint"> + + <refentryinfo> + <title>kdbus.endpoint</title> + <productname>kdbus.endpoint</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus.endpoint</refname> + <refpurpose>kdbus endpoint</refpurpose> + </refnamediv> + + <refsect1> + <title>Description</title> + + <para> + Endpoints are entry points to a bus (see + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>). + By default, each bus has a default + endpoint called 'bus'. The bus owner has the ability to create custom + endpoints with specific names, permissions, and policy databases + (see below). An endpoint is presented as file underneath the directory + of the parent bus. + </para> + <para> + To create a custom endpoint, open the default endpoint + (<literal>bus</literal>) and use the + <constant>KDBUS_CMD_ENDPOINT_MAKE</constant> ioctl with + <type>struct kdbus_cmd</type>. Custom endpoints always have a policy + database that, by default, forbids any operation. You have to explicitly + install policy entries to allow any operation on this endpoint. + </para> + <para> + Once <constant>KDBUS_CMD_ENDPOINT_MAKE</constant> succeeded, the new + endpoint will appear in the filesystem + (<citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>), and the used file descriptor will manage the + newly created endpoint resource. It cannot be used to manage further + resources and must be kept open as long as the endpoint is needed. The + endpoint will be terminated as soon as the file descriptor is closed. + </para> + <para> + Endpoint names may be chosen freely except for one restriction: the name + must be prefixed with the numeric effective UID of the creator and a dash. + This is required to avoid namespace clashes between different users. When + creating an endpoint, the name that is passed in must be properly + formatted or the kernel will refuse creation of the endpoint. Example: + <literal>1047-my-endpoint</literal> is an acceptable name for an + endpoint registered by a user with UID 1047. However, + <literal>1024-my-endpoint</literal> is not, and neither is + <literal>my-endpoint</literal>. The UID must be provided in the + user-namespace of the bus. + </para> + <para> + To create connections to a bus, use <constant>KDBUS_CMD_HELLO</constant> + on a file descriptor returned by <function>open()</function> on an + endpoint node. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for further details. + </para> + </refsect1> + + <refsect1> + <title>Creating custom endpoints</title> + <para> + To create a new endpoint, the + <constant>KDBUS_CMD_ENDPOINT_MAKE</constant> command is used. Along with + the endpoint's name, which will be used to expose the endpoint in the + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>, + the command also optionally takes items to set up the endpoint's + <citerefentry> + <refentrytitle>kdbus.policy</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + <constant>KDBUS_CMD_ENDPOINT_MAKE</constant> takes a + <type>struct kdbus_cmd</type> argument. + </para> + <programlisting> +struct kdbus_cmd { + __u64 size; + __u64 flags; + __u64 return_flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para>The flags for creation.</para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_MAKE_ACCESS_GROUP</constant></term> + <listitem> + <para>Make the endpoint file group-accessible.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_MAKE_ACCESS_WORLD</constant></term> + <listitem> + <para>Make the endpoint file world-accessible.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_FLAG_NEGOTIATE</constant></term> + <listitem> + <para> + Requests a set of valid flags for this ioctl. When this bit is + set, no action is taken; the ioctl will return + <errorcode>0</errorcode>, and the <varname>flags</varname> + field will have all bits set that are valid for this command. + The <constant>KDBUS_FLAG_NEGOTIATE</constant> bit will be + cleared by the operation. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + The following items are expected for + <constant>KDBUS_CMD_ENDPOINT_MAKE</constant>. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_MAKE_NAME</constant></term> + <listitem> + <para>Contains a string to identify the endpoint name.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NAME</constant></term> + <term><constant>KDBUS_ITEM_POLICY_ACCESS</constant></term> + <listitem> + <para> + These items are used to set the policy attached to the + endpoint. For more details on bus and endpoint policies, see + <citerefentry> + <refentrytitle>kdbus.policy</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para> + </listitem> + </varlistentry> + </variablelist> + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <varname>EINVAL</varname>. + </para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Updating endpoints</title> + <para> + To update an existing endpoint, the + <constant>KDBUS_CMD_ENDPOINT_UPDATE</constant> command is used on the file + descriptor that was used to create the update, using + <constant>KDBUS_CMD_ENDPOINT_MAKE</constant>. The only relevant detail of + the endpoint that can be updated is the policy. When the command is + employed, the policy of the endpoint is <emphasis>replaced</emphasis> + atomically with the new set of rules. + The command takes a <type>struct kdbus_cmd</type> argument. + </para> + <programlisting> +struct kdbus_cmd { + __u64 size; + __u64 flags; + __u64 return_flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para> + Unused for this command. + <constant>KDBUS_FLAG_NEGOTIATE</constant> is accepted to probe for + valid flags. If set, the ioctl will return <errorcode>0</errorcode>, + and the <varname>flags</varname> field is set to + <constant>0</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + The following items are expected for + <constant>KDBUS_CMD_ENDPOINT_UPDATE</constant>. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_NAME</constant></term> + <term><constant>KDBUS_ITEM_POLICY_ACCESS</constant></term> + <listitem> + <para> + These items are used to set the policy attached to the + endpoint. For more details on bus and endpoint policies, see + <citerefentry> + <refentrytitle>kdbus.policy</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + Existing policy is atomically replaced with the new rules + provided. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NEGOTIATE</constant></term> + <listitem><para> + With this item, programs can <emphasis>probe</emphasis> the + kernel for known item types. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para></listitem> + </varlistentry> + </variablelist> + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <constant>EINVAL</constant>. + </para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Return value</title> + <para> + On success, all mentioned ioctl commands return <errorcode>0</errorcode>; + on error, <errorcode>-1</errorcode> is returned, and + <varname>errno</varname> is set to indicate the error. + If the issued ioctl is illegal for the file descriptor used, + <varname>errno</varname> will be set to <constant>ENOTTY</constant>. + </para> + + <refsect2> + <title> + <constant>KDBUS_CMD_ENDPOINT_MAKE</constant> may fail with the + following errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + The flags supplied in the <type>struct kdbus_cmd</type> + are invalid. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Illegal combination of <constant>KDBUS_ITEM_NAME</constant> and + <constant>KDBUS_ITEM_POLICY_ACCESS</constant> was provided. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EEXIST</constant></term> + <listitem><para> + An endpoint of that name already exists. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EPERM</constant></term> + <listitem><para> + The calling user is not privileged. See + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for information about privileged users. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title> + <constant>KDBUS_CMD_ENDPOINT_UPDATE</constant> may fail with the + following errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + The flags supplied in <type>struct kdbus_cmd</type> + are invalid. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Illegal combination of <constant>KDBUS_ITEM_NAME</constant> and + <constant>KDBUS_ITEM_POLICY_ACCESS</constant> was provided. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EEXIST</constant></term> + <listitem><para> + An endpoint of that name already exists. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + </simplelist> + </refsect1> +</refentry> diff --git a/Documentation/kdbus/kdbus.fs.xml b/Documentation/kdbus/kdbus.fs.xml new file mode 100644 index 00000000000..8c2a90e10b6 --- /dev/null +++ b/Documentation/kdbus/kdbus.fs.xml @@ -0,0 +1,124 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus_fs"> + + <refentryinfo> + <title>kdbus.fs</title> + <productname>kdbus.fs</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus.fs</refname> + <refpurpose>kdbus file system</refpurpose> + </refnamediv> + + <refsect1> + <title>File-system Layout</title> + + <para> + The <emphasis>kdbusfs</emphasis> pseudo filesystem provides access to + kdbus entities, such as <emphasis>buses</emphasis> and + <emphasis>endpoints</emphasis>. Each time the filesystem is mounted, + a new, isolated kdbus instance is created, which is independent from the + other instances. + </para> + <para> + The system-wide standard mount point for <emphasis>kdbusfs</emphasis> is + <constant>/sys/fs/kdbus</constant>. + </para> + + <para> + Buses are represented as directories in the file system layout, whereas + endpoints are exposed as files inside these directories. At the top-level, + a <emphasis>control</emphasis> node is present, which can be opened to + create new buses via the <constant>KDBUS_CMD_BUS_MAKE</constant> ioctl. + Each <emphasis>bus</emphasis> shows a default endpoint called + <varname>bus</varname>, which can be opened to either create a connection + with the <constant>KDBUS_CMD_HELLO</constant> ioctl, or to create new + custom endpoints for the bus with + <constant>KDBUS_CMD_ENDPOINT_MAKE</constant>. See + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>, + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> and + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + + <para>Following, you can see an example layout of the + <emphasis>kdbusfs</emphasis> filesystem:</para> + +<programlisting> + /sys/fs/kdbus/ ; mount-point + |-- 0-system ; bus directory + | |-- bus ; default endpoint + | `-- 1017-custom ; custom endpoint + |-- 1000-user ; bus directory + | |-- bus ; default endpoint + | |-- 1000-service-A ; custom endpoint + | `-- 1000-service-B ; custom endpoint + `-- control ; control file +</programlisting> + </refsect1> + + <refsect1> + <title>Mounting instances</title> + <para> + In order to get a new and separate kdbus environment, a new instance + of <emphasis>kdbusfs</emphasis> can be mounted like this: + </para> +<programlisting> + # mount -t kdbusfs kdbusfs /tmp/new_kdbus/ +</programlisting> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>mount</refentrytitle> + <manvolnum>8</manvolnum> + </citerefentry> + </member> + </simplelist> + </refsect1> +</refentry> diff --git a/Documentation/kdbus/kdbus.item.xml b/Documentation/kdbus/kdbus.item.xml new file mode 100644 index 00000000000..bfe47362097 --- /dev/null +++ b/Documentation/kdbus/kdbus.item.xml @@ -0,0 +1,840 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus"> + + <refentryinfo> + <title>kdbus.item</title> + <productname>kdbus item</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus.item</refname> + <refpurpose>kdbus item structure, layout and usage</refpurpose> + </refnamediv> + + <refsect1> + <title>Description</title> + + <para> + To flexibly augment transport structures, data blobs of type + <type>struct kdbus_item</type> can be attached to the structs passed + into the ioctls. Some ioctls make items of certain types mandatory, + others are optional. Items that are unsupported by ioctls they are + attached to will cause the ioctl to fail with <varname>errno</varname> + set to <constant>EINVAL</constant>. + Items are also used for information stored in a connection's + <emphasis>pool</emphasis>, such as received messages, name lists or + requested connection or bus owner information. Depending on the type of + an item, its total size is either fixed or variable. + </para> + + <refsect2> + <title>Chaining items</title> + <para> + Whenever items are used as part of the kdbus kernel API, they are + embedded in structs that are embedded inside structs that themselves + include a size field containing the overall size of the structure. + This allows multiple items to be chained up, and an item iterator + (see below) is capable of detecting the end of an item chain. + </para> + </refsect2> + + <refsect2> + <title>Alignment</title> + <para> + The kernel expects all items to be aligned to 8-byte boundaries. + Unaligned items will cause the ioctl they are used with to fail + with <varname>errno</varname> set to <constant>EINVAL</constant>. + An item that has an unaligned size itself hence needs to be padded + if it is followed by another item. + </para> + </refsect2> + + <refsect2> + <title>Iterating items</title> + <para> + A simple iterator would iterate over the items until the items have + reached the embedding structure's overall size. An example + implementation is shown below. + </para> + + <programlisting><![CDATA[ +#define KDBUS_ALIGN8(val) (((val) + 7) & ~7) + +#define KDBUS_ITEM_NEXT(item) \ + (typeof(item))(((uint8_t *)item) + KDBUS_ALIGN8((item)->size)) + +#define KDBUS_ITEM_FOREACH(item, head, first) \ + for (item = (head)->first; \ + ((uint8_t *)(item) < (uint8_t *)(head) + (head)->size) && \ + ((uint8_t *)(item) >= (uint8_t *)(head)); \ + item = KDBUS_ITEM_NEXT(item)) + ]]></programlisting> + </refsect2> + </refsect1> + + <refsect1> + <title>Item layout</title> + <para> + A <type>struct kdbus_item</type> consists of a + <varname>size</varname> field, describing its overall size, and a + <varname>type</varname> field, both 64 bit wide. They are followed by + a union to store information that is specific to the item's type. + The struct layout is shown below. + </para> + + <programlisting> +struct kdbus_item { + __u64 size; + __u64 type; + /* item payload - see below */ + union { + __u8 data[0]; + __u32 data32[0]; + __u64 data64[0]; + char str[0]; + + __u64 id; + struct kdbus_vec vec; + struct kdbus_creds creds; + struct kdbus_pids pids; + struct kdbus_audit audit; + struct kdbus_caps caps; + struct kdbus_timestamp timestamp; + struct kdbus_name name; + struct kdbus_bloom_parameter bloom_parameter; + struct kdbus_bloom_filter bloom_filter; + struct kdbus_memfd memfd; + int fds[0]; + struct kdbus_notify_name_change name_change; + struct kdbus_notify_id_change id_change; + struct kdbus_policy_access policy_access; + }; +}; + </programlisting> + + <para> + <type>struct kdbus_item</type> should never be used to allocate + an item instance, as its size may grow in future releases of the API. + Instead, it should be manually assembled by storing the + <varname>size</varname>, <varname>type</varname> and payload to a + struct of its own. + </para> + </refsect1> + + <refsect1> + <title>Item types</title> + + <refsect2> + <title>Negotiation item</title> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_NEGOTIATE</constant></term> + <listitem><para> + With this item is attached to any ioctl, programs can + <emphasis>probe</emphasis> the kernel for known item items. + The item carries an array of <type>uint64_t</type> values in + <varname>item.data64</varname>, each set to an item type to + probe. The kernel will reset each member of this array that is + not recognized as valid item type to <constant>0</constant>. + This way, users can negotiate kernel features at start-up to + keep newer userspace compatible with older kernels. This item + is never attached by the kernel in response to any command. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title>Command specific items</title> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_PAYLOAD_VEC</constant></term> + <term><constant>KDBUS_ITEM_PAYLOAD_OFF</constant></term> + <listitem><para> + Messages are directly copied by the sending process into the + receiver's + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + This way, two peers can exchange data by effectively doing a + single-copy from one process to another; the kernel will not buffer + the data anywhere else. <constant>KDBUS_ITEM_PAYLOAD_VEC</constant> + is used when <emphasis>sending</emphasis> message. The item + references a memory address when the payload data can be found. + <constant>KDBUS_ITEM_PAYLOAD_OFF</constant> is used when messages + are <emphasis>received</emphasis>, and the + <constant>offset</constant> value describes the offset inside the + receiving connection's + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + where the message payload can be found. See + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on passing of payload data along with a + message. + <programlisting> +struct kdbus_vec { + __u64 size; + union { + __u64 address; + __u64 offset; + }; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_PAYLOAD_MEMFD</constant></term> + <listitem><para> + Transports a file descriptor of a <emphasis>memfd</emphasis> in + <type>struct kdbus_memfd</type> in <varname>item.memfd</varname>. + The <varname>size</varname> field has to match the actual size of + the memfd that was specified when it was created. The + <varname>start</varname> parameter denotes the offset inside the + memfd at which the referenced payload starts. See + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on passing of payload data along with a + message. + <programlisting> +struct kdbus_memfd { + __u64 start; + __u64 size; + int fd; + __u32 __pad; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_FDS</constant></term> + <listitem><para> + Contains an array of <emphasis>file descriptors</emphasis>. + When used with <constant>KDBUS_CMD_SEND</constant>, the values of + this array must be filled with valid file descriptor numbers. + When received as item attached to a message, the array will + contain the numbers of the installed file descriptors, or + <constant>-1</constant> in case an error occurred. + file descriptor. + In either case, the number of entries in the array is derived from + the item's total size. See + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title>Items specific to some commands</title> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_CANCEL_FD</constant></term> + <listitem><para> + Transports a file descriptor that can be used to cancel a + synchronous <constant>KDBUS_CMD_SEND</constant> operation by + writing to it. The file descriptor is stored in + <varname>item.fd[0]</varname>. The item may only contain one + file descriptor. See + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on this item and how to use it. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_BLOOM_PARAMETER</constant></term> + <listitem><para> + Contains a set of <emphasis>bloom parameters</emphasis> as + <type>struct kdbus_bloom_parameter</type> in + <varname>item.bloom_parameter</varname>. + The item is passed from userspace to kernel during the + <constant>KDBUS_CMD_BUS_MAKE</constant> ioctl, and returned + verbatim when <constant>KDBUS_CMD_HELLO</constant> is called. + The kernel does not use the bloom parameters, but they need to + be known by each connection on the bus in order to define the + bloom filter hash details. See + <citerefentry> + <refentrytitle>kdbus.match</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on matching and bloom filters. + <programlisting> +struct kdbus_bloom_parameter { + __u64 size; + __u64 n_hash; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_BLOOM_FILTER</constant></term> + <listitem><para> + Carries a <emphasis>bloom filter</emphasis> as + <type>struct kdbus_bloom_filter</type> in + <varname>item.bloom_filter</varname>. It is mandatory to send this + item attached to a <type>struct kdbus_msg</type>, in case the + message is a signal. This item is never transported from kernel to + userspace. See + <citerefentry> + <refentrytitle>kdbus.match</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on matching and bloom filters. + <programlisting> +struct kdbus_bloom_filter { + __u64 generation; + __u64 data[0]; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_BLOOM_MASK</constant></term> + <listitem><para> + Transports a <emphasis>bloom mask</emphasis> as binary data blob + stored in <varname>item.data</varname>. This item is used to + describe a match into a connection's match database. See + <citerefentry> + <refentrytitle>kdbus.match</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on matching and bloom filters. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_DST_NAME</constant></term> + <listitem><para> + Contains a <emphasis>well-known name</emphasis> to send a + message to, as null-terminated string in + <varname>item.str</varname>. This item is used with + <constant>KDBUS_CMD_SEND</constant>. See + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on how to send a message. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_MAKE_NAME</constant></term> + <listitem><para> + Contains a <emphasis>bus name</emphasis> or + <emphasis>endpoint name</emphasis>, stored as null-terminated + string in <varname>item.str</varname>. This item is sent from + userspace to kernel when buses or endpoints are created, and + returned back to userspace when the bus creator information is + queried. See + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + and + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_ATTACH_FLAGS_SEND</constant></term> + <term><constant>KDBUS_ITEM_ATTACH_FLAGS_RECV</constant></term> + <listitem><para> + Contains a set of <emphasis>attach flags</emphasis> at + <emphasis>send</emphasis> or <emphasis>receive</emphasis> time. See + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>, + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> and + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on attach flags. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_ID</constant></term> + <listitem><para> + Transports a connection's <emphasis>numerical ID</emphasis> of + a connection as <type>uint64_t</type> value in + <varname>item.id</varname>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NAME</constant></term> + <listitem><para> + Transports a name associated with the + <emphasis>name registry</emphasis> as null-terminated string as + <type>struct kdbus_name</type> in + <varname>item.name</varname>. The <varname>flags</varname> + contains the flags of the name. See + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on how to access the name registry of a bus. + <programlisting> +struct kdbus_name { + __u64 flags; + char name[0]; +}; + </programlisting> + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title>Items attached by the kernel as metadata</title> + + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_TIMESTAMP</constant></term> + <listitem><para> + Contains both the <emphasis>monotonic</emphasis> and the + <emphasis>realtime</emphasis> timestamp, taken when the message + was processed on the kernel side. + Stored as <type>struct kdbus_timestamp</type> in + <varname>item.timestamp</varname>. + <programlisting> +struct kdbus_timestamp { + __u64 seqnum; + __u64 monotonic_ns; + __u64 realtime_ns; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_CREDS</constant></term> + <listitem><para> + Contains a set of <emphasis>user</emphasis> and + <emphasis>group</emphasis> information as 32-bit values, in the + usual four flavors: real, effective, saved and filesystem related. + Stored as <type>struct kdbus_creds</type> in + <varname>item.creds</varname>. + <programlisting> +struct kdbus_creds { + __u32 uid; + __u32 euid; + __u32 suid; + __u32 fsuid; + __u32 gid; + __u32 egid; + __u32 sgid; + __u32 fsgid; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_PIDS</constant></term> + <listitem><para> + Contains the <emphasis>PID</emphasis>, <emphasis>TID</emphasis> + and <emphasis>parent PID (PPID)</emphasis> of a remote peer. + Stored as <type>struct kdbus_pids</type> in + <varname>item.pids</varname>. + <programlisting> +struct kdbus_pids { + __u64 pid; + __u64 tid; + __u64 ppid; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_AUXGROUPS</constant></term> + <listitem><para> + Contains the <emphasis>auxiliary (supplementary) groups</emphasis> + a remote peer is a member of, stored as array of + <type>uint32_t</type> values in <varname>item.data32</varname>. + The array length can be determined by looking at the item's total + size, subtracting the size of the header and and dividing the + remainder by <constant>sizeof(uint32_t)</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_OWNED_NAME</constant></term> + <listitem><para> + Contains a <emphasis>well-known name</emphasis> currently owned + by a connection. The name is stored as null-terminated string in + <varname>item.str</varname>. Its length can also be derived from + the item's total size. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_TID_COMM</constant> [*]</term> + <listitem><para> + Contains the <emphasis>comm</emphasis> string of a task's + <emphasis>TID</emphasis> (thread ID), stored as null-terminated + string in <varname>item.str</varname>. Its length can also be + derived from the item's total size. Receivers of this item should + not use its contents for any kind of security measures. See below. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_PID_COMM</constant> [*]</term> + <listitem><para> + Contains the <emphasis>comm</emphasis> string of a task's + <emphasis>PID</emphasis> (process ID), stored as null-terminated + string in <varname>item.str</varname>. Its length can also be + derived from the item's total size. Receivers of this item should + not use its contents for any kind of security measures. See below. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_EXE</constant> [*]</term> + <listitem><para> + Contains the <emphasis>path to the executable</emphasis> of a task, + stored as null-terminated string in <varname>item.str</varname>. Its + length can also be derived from the item's total size. Receivers of + this item should not use its contents for any kind of security + measures. See below. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_CMDLINE</constant> [*]</term> + <listitem><para> + Contains the <emphasis>command line arguments</emphasis> of a + task, stored as an <emphasis>array</emphasis> of null-terminated + strings in <varname>item.str</varname>. The total length of all + strings in the array can be derived from the item's total size. + Receivers of this item should not use its contents for any kind + of security measures. See below. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_CGROUP</constant></term> + <listitem><para> + Contains the <emphasis>cgroup path</emphasis> of a task, stored + as null-terminated string in <varname>item.str</varname>. Its + length can also be derived from the item's total size. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_CAPS</constant></term> + <listitem><para> + Contains sets of <emphasis>capabilities</emphasis>, stored as + <type>struct kdbus_caps</type> in <varname>item.caps</varname>. + As the item size may increase in the future, programs should be + written in a way that it takes + <varname>item.caps.last_cap</varname> into account, and derive + the number of sets and rows from the item size and the reported + number of valid capability bits. + <programlisting> +struct kdbus_caps { + __u32 last_cap; + __u32 caps[0]; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_SECLABEL</constant></term> + <listitem><para> + Contains the <emphasis>LSM label</emphasis> of a task, stored as + null-terminated string in <varname>item.str</varname>. Its length + can also be derived from the item's total size. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_AUDIT</constant></term> + <listitem><para> + Contains the audit <emphasis>sessionid</emphasis> and + <emphasis>loginuid</emphasis> of a task, stored as + <type>struct kdbus_audit</type> in + <varname>item.audit</varname>. + <programlisting> +struct kdbus_audit { + __u32 sessionid; + __u32 loginuid; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_CONN_DESCRIPTION</constant></term> + <listitem><para> + Contains the <emphasis>connection description</emphasis>, as set + by <constant>KDBUS_CMD_HELLO</constant> or + <constant>KDBUS_CMD_CONN_UPDATE</constant>, stored as + null-terminated string in <varname>item.str</varname>. Its length + can also be derived from the item's total size. + </para></listitem> + </varlistentry> + </variablelist> + + <para> + All metadata is automatically translated into the + <emphasis>namespaces</emphasis> of the task that receives them. See + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information. + </para> + + <para> + [*] Note that the content stored in metadata items of type + <constant>KDBUS_ITEM_TID_COMM</constant>, + <constant>KDBUS_ITEM_PID_COMM</constant>, + <constant>KDBUS_ITEM_EXE</constant> and + <constant>KDBUS_ITEM_CMDLINE</constant> + can easily be tampered by the sending tasks. Therefore, they should + <emphasis>not</emphasis> be used for any sort of security relevant + assumptions. The only reason they are transmitted is to let + receivers know about details that were set when metadata was + collected, even though the task they were collected from is not + active any longer when the items are received. + </para> + </refsect2> + + <refsect2> + <title>Items used for policy entries, matches and notifications</title> + + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_POLICY_ACCESS</constant></term> + <listitem><para> + This item describes a <emphasis>policy access</emphasis> entry to + access the policy database of a + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> or + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + Please refer to + <citerefentry> + <refentrytitle>kdbus.policy</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on the policy database and how to access it. + <programlisting> +struct kdbus_policy_access { + __u64 type; + __u64 access; + __u64 id; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_ID_ADD</constant></term> + <term><constant>KDBUS_ITEM_ID_REMOVE</constant></term> + <listitem><para> + This item is sent as attachment to a + <emphasis>kernel notification</emphasis> and indicates that a + new connection was created on the bus, or that a connection was + disconnected, respectively. It stores a + <type>struct kdbus_notify_id_change</type> in + <varname>item.id_change</varname>. + The <varname>id</varname> field contains the numeric ID of the + connection that was added or removed, and <varname>flags</varname> + is set to the connection flags, as passed by + <constant>KDBUS_CMD_HELLO</constant>. See + <citerefentry> + <refentrytitle>kdbus.match</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + and + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on matches and notification messages. + <programlisting> +struct kdbus_notify_id_change { + __u64 id; + __u64 flags; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NAME_ADD</constant></term> + <term><constant>KDBUS_ITEM_NAME_REMOVE</constant></term> + <term><constant>KDBUS_ITEM_NAME_CHANGE</constant></term> + <listitem><para> + This item is sent as attachment to a + <emphasis>kernel notification</emphasis> and indicates that a + <emphasis>well-known name</emphasis> appeared, disappeared or + transferred to another owner on the bus. It stores a + <type>struct kdbus_notify_name_change</type> in + <varname>item.name_change</varname>. + <varname>old_id</varname> describes the former owner of the name + and is set to <constant>0</constant> values in case of + <constant>KDBUS_ITEM_NAME_ADD</constant>. + <varname>new_id</varname> describes the new owner of the name and + is set to <constant>0</constant> values in case of + <constant>KDBUS_ITEM_NAME_REMOVE</constant>. + The <varname>name</varname> field contains the well-known name the + notification is about, as null-terminated string. See + <citerefentry> + <refentrytitle>kdbus.match</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + and + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on matches and notification messages. + <programlisting> +struct kdbus_notify_name_change { + struct kdbus_notify_id_change old_id; + struct kdbus_notify_id_change new_id; + char name[0]; +}; + </programlisting> + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_REPLY_TIMEOUT</constant></term> + <listitem><para> + This item is sent as attachment to a + <emphasis>kernel notification</emphasis>. It informs the receiver + that an expected reply to a message was not received in time. + The remote peer ID and the message cookie is stored in the message + header. See + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information about messages, timeouts and notifications. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_REPLY_DEAD</constant></term> + <listitem><para> + This item is sent as attachment to a + <emphasis>kernel notification</emphasis>. It informs the receiver + that a remote connection a reply is expected from was disconnected + before that reply was sent. The remote peer ID and the message + cookie is stored in the message header. See + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information about messages, timeouts and notifications. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>memfd_create</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + </simplelist> + </refsect1> + +</refentry> diff --git a/Documentation/kdbus/kdbus.match.xml b/Documentation/kdbus/kdbus.match.xml new file mode 100644 index 00000000000..ef77b64e589 --- /dev/null +++ b/Documentation/kdbus/kdbus.match.xml @@ -0,0 +1,553 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus.match"> + + <refentryinfo> + <title>kdbus.match</title> + <productname>kdbus.match</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus.match</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus.match</refname> + <refpurpose>kdbus match</refpurpose> + </refnamediv> + + <refsect1> + <title>Description</title> + + <para> + kdbus connections can install matches in order to subscribe to signal + messages sent on the bus. Such signal messages can be either directed + to a single connection (by setting a specific connection ID in + <varname>struct kdbus_msg.dst_id</varname> or by sending it to a + well-known name), or to potentially <emphasis>all</emphasis> currently + active connections on the bus (by setting + <varname>struct kdbus_msg.dst_id</varname> to + <constant>KDBUS_DST_ID_BROADCAST</constant>). + A signal message always has the <constant>KDBUS_MSG_SIGNAL</constant> + bit set in the <varname>flags</varname> bitfield. + Also, signal messages can originate from either the kernel (called + <emphasis>notifications</emphasis>), or from other bus connections. + In either case, a bus connection needs to have a suitable + <emphasis>match</emphasis> installed in order to receive any signal + message. Without any rules installed in the connection, no signal message + will be received. + </para> + </refsect1> + + <refsect1> + <title>Matches for signal messages from other connections</title> + <para> + Matches for messages from other connections (not kernel notifications) + are implemented as bloom filters (see below). The sender adds certain + properties of the message as elements to a bloom filter bit field, and + sends that along with the signal message. + + The receiving connection adds the message properties it is interested in + as elements to a bloom mask bit field, and uploads the mask as match rule, + possibly along with some other rules to further limit the match. + + The kernel will match the signal message's bloom filter against the + connections bloom mask (simply by &-ing it), and will decide whether + the message should be delivered to a connection. + </para> + <para> + The kernel has no notion of any specific properties of the signal message, + all it sees are the bit fields of the bloom filter and the mask to match + against. The use of bloom filters allows simple and efficient matching, + without exposing any message properties or internals to the kernel side. + Clients need to deal with the fact that they might receive signal messages + which they did not subscribe to, as the bloom filter might allow + false-positives to pass the filter. + + To allow the future extension of the set of elements in the bloom filter, + the filter specifies a <emphasis>generation</emphasis> number. A later + generation must always contain all elements of the set of the previous + generation, but can add new elements to the set. The match rules mask can + carry an array with all previous generations of masks individually stored. + When the filter and mask are matched by the kernel, the mask with the + closest matching generation is selected as the index into the mask array. + </para> + </refsect1> + + <refsect1> + <title>Bloom filters</title> + <para> + Bloom filters allow checking whether a given word is present in a + dictionary. This allows connections to set up a mask for information it + is interested in, and will be delivered signal messages that have a + matching filter. + + For general information, see + <ulink url="https://en.wikipedia.org/wiki/Bloom_filter">the Wikipedia + article on bloom filters</ulink>. + </para> + <para> + The size of the bloom filter is defined per bus when it is created, in + <varname>kdbus_bloom_parameter.size</varname>. All bloom filters attached + to signal messages on the bus must match this size, and all bloom filter + matches uploaded by connections must also match the size, or a multiple + thereof (see below). + + The calculation of the mask has to be done in userspace applications. The + kernel just checks the bitmasks to decide whether or not to let the + message pass. All bits in the mask must match the filter in and bit-wise + <emphasis>AND</emphasis> logic, but the mask may have more bits set than + the filter. Consequently, false positive matches are expected to happen, + and programs must deal with that fact by checking the contents of the + payload again at receive time. + </para> + <para> + Masks are entities that are always passed to the kernel as part of a + match (with an item of type <constant>KDBUS_ITEM_BLOOM_MASK</constant>), + and filters can be attached to signals, with an item of type + <constant>KDBUS_ITEM_BLOOM_FILTER</constant>. For a filter to match, all + its bits have to be set in the match mask as well. + </para> + <para> + For example, consider a bus that has a bloom size of 8 bytes, and the + following mask/filter combinations: + </para> + <programlisting><![CDATA[ + filter 0x0101010101010101 + mask 0x0101010101010101 + -> matches + + filter 0x0303030303030303 + mask 0x0101010101010101 + -> doesn't match + + filter 0x0101010101010101 + mask 0x0303030303030303 + -> matches + ]]></programlisting> + + <para> + Hence, in order to catch all messages, a mask filled with + <constant>0xff</constant> bytes can be installed as a wildcard match rule. + </para> + + <refsect2> + <title>Generations</title> + + <para> + Uploaded matches may contain multiple masks, which have are as large as + the bloom size defined by the bus. Each block of a mask is called a + <emphasis>generation</emphasis>, starting at index 0. + + At match time, when a signal is about to be delivered, a bloom mask + generation is passed, which denotes which of the bloom masks the filter + should be matched against. This allows programs to provide backward + compatible masks at upload time, while older clients can still match + against older versions of filters. + </para> + </refsect2> + </refsect1> + + <refsect1> + <title>Matches for kernel notifications</title> + <para> + To receive kernel generated notifications (see + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>), + a connection must install match rules that are different from + the bloom filter matches described in the section above. They can be + filtered by the connection ID that caused the notification to be sent, by + one of the names it currently owns, or by the type of the notification + (ID/name add/remove/change). + </para> + </refsect1> + + <refsect1> + <title>Adding a match</title> + <para> + To add a match, the <constant>KDBUS_CMD_MATCH_ADD</constant> ioctl is + used, which takes a struct of the struct described below. + + Note that each of the items attached to this command will internally + create one match <emphasis>rule</emphasis>, and the collection of them, + which is submitted as one block via the ioctl, is called a + <emphasis>match</emphasis>. To allow a message to pass, all rules of a + match have to be satisfied. Hence, adding more items to the command will + only narrow the possibility of a match to effectively let the message + pass, and will decrease the chance that the connection's process will be + woken up needlessly. + + Multiple matches can be installed per connection. As long as one of it has + a set of rules which allows the message to pass, this one will be + decisive. + </para> + + <programlisting> +struct kdbus_cmd_match { + __u64 size; + __u64 flags; + __u64 return_flags; + __u64 cookie; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para>Flags to control the behavior of the ioctl.</para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_MATCH_REPLACE</constant></term> + <listitem> + <para>Make the endpoint file group-accessible</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_FLAG_NEGOTIATE</constant></term> + <listitem> + <para> + Requests a set of valid flags for this ioctl. When this bit is + set, no action is taken; the ioctl will return + <errorcode>0</errorcode>, and the <varname>flags</varname> + field will have all bits set that are valid for this command. + The <constant>KDBUS_FLAG_NEGOTIATE</constant> bit will be + cleared by the operation. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>cookie</varname></term> + <listitem><para> + A cookie which identifies the match, so it can be referred to when + removing it. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + Items to define the actual rules of the matches. The following item + types are expected. Each item will create one new match rule. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_BLOOM_MASK</constant></term> + <listitem> + <para> + An item that carries the bloom filter mask to match against + in its data field. The payload size must match the bloom + filter size that was specified when the bus was created. + See the section below for more information on bloom filters. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NAME</constant></term> + <listitem> + <para> + When used as part of kernel notifications, this item specifies + a name that is acquired, lost or that changed its owner (see + below). When used as part of a match for user-generated signal + messages, it specifies a name that the sending connection must + own at the time of sending the signal. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_ID</constant></term> + <listitem> + <para> + Specify a sender connection's ID that will match this rule. + For kernel notifications, this specifies the ID of a + connection that was added to or removed from the bus. + For used-generated signals, it specifies the ID of the + connection that sent the signal message. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NAME_ADD</constant></term> + <term><constant>KDBUS_ITEM_NAME_REMOVE</constant></term> + <term><constant>KDBUS_ITEM_NAME_CHANGE</constant></term> + <listitem> + <para> + These items request delivery of kernel notifications that + describe a name acquisition, loss, or change. The details + are stored in the item's + <varname>kdbus_notify_name_change</varname> member. + All information specified must be matched in order to make + the message pass. Use + <constant>KDBUS_MATCH_ID_ANY</constant> to + match against any unique connection ID. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_ID_ADD</constant></term> + <term><constant>KDBUS_ITEM_ID_REMOVE</constant></term> + <listitem> + <para> + These items request delivery of kernel notifications that are + generated when a connection is created or terminated. + <type>struct kdbus_notify_id_change</type> is used to + store the actual match information. This item can be used to + monitor one particular connection ID, or, when the ID field + is set to <constant>KDBUS_MATCH_ID_ANY</constant>, + all of them. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_NEGOTIATE</constant></term> + <listitem><para> + With this item, programs can <emphasis>probe</emphasis> the + kernel for known item types. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para></listitem> + </varlistentry> + </variablelist> + + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <constant>EINVAL</constant>. + </para> + </listitem> + </varlistentry> + </variablelist> + + <para> + Refer to + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on message types. + </para> + </refsect1> + + <refsect1> + <title>Removing a match</title> + <para> + Matches can be removed with the + <constant>KDBUS_CMD_MATCH_REMOVE</constant> ioctl, which takes + <type>struct kdbus_cmd_match</type> as argument, but its fields + usage slightly differs compared to that of + <constant>KDBUS_CMD_MATCH_ADD</constant>. + </para> + + <programlisting> +struct kdbus_cmd_match { + __u64 size; + __u64 cookie; + __u64 flags; + __u64 return_flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>cookie</varname></term> + <listitem><para> + The cookie of the match, as it was passed when the match was added. + All matches that have this cookie will be removed. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para> + No flags are supported for this use case. + <constant>KDBUS_FLAG_NEGOTIATE</constant> is accepted to probe for + valid flags. If set, the ioctl will fail with + <errorcode>-1</errorcode>, <varname>errno</varname> is set to + <constant>EPROTO</constant>, and the <varname>flags</varname> field + is set to <constant>0</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + No items are supported for this use case, but + <constant>KDBUS_ITEM_NEGOTIATE</constant> is allowed nevertheless. + </para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Return value</title> + <para> + On success, all mentioned ioctl commands return <errorcode>0</errorcode>; + on error, <errorcode>-1</errorcode> is returned, and + <varname>errno</varname> is set to indicate the error. + If the issued ioctl is illegal for the file descriptor used, + <varname>errno</varname> will be set to <constant>ENOTTY</constant>. + </para> + + <refsect2> + <title> + <constant>KDBUS_CMD_MATCH_ADD</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Illegal flags or items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EDOM</constant></term> + <listitem><para> + Illegal bloom filter size. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EMFILE</constant></term> + <listitem><para> + Too many matches for this connection. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title> + <constant>KDBUS_CMD_MATCH_REMOVE</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Illegal flags. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EBADSLT</constant></term> + <listitem><para> + A match entry with the given cookie could not be found. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.match</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + </simplelist> + </refsect1> +</refentry> diff --git a/Documentation/kdbus/kdbus.message.xml b/Documentation/kdbus/kdbus.message.xml new file mode 100644 index 00000000000..c25000dcfbc --- /dev/null +++ b/Documentation/kdbus/kdbus.message.xml @@ -0,0 +1,1277 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus.message"> + + <refentryinfo> + <title>kdbus.message</title> + <productname>kdbus.message</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus.message</refname> + <refpurpose>kdbus message</refpurpose> + </refnamediv> + + <refsect1> + <title>Description</title> + + <para> + A kdbus message is used to exchange information between two connections + on a bus, or to transport notifications from the kernel to one or many + connections. This document describes the layout of messages, how payload + is added to them and how they are sent and received. + </para> + </refsect1> + + <refsect1> + <title>Message layout</title> + + <para>The layout of a message is shown below.</para> + + <programlisting> + +-------------------------------------------------------------------------+ + | Message | + | +---------------------------------------------------------------------+ | + | | Header | | + | | size: overall message size, including the data records | | + | | destination: connection ID of the receiver | | + | | source: connection ID of the sender (set by kernel) | | + | | payload_type: "DBusDBus" textual identifier stored as uint64_t | | + | +---------------------------------------------------------------------+ | + | +---------------------------------------------------------------------+ | + | | Data Record | | + | | size: overall record size (without padding) | | + | | type: type of data | | + | | data: reference to data (address or file descriptor) | | + | +---------------------------------------------------------------------+ | + | +---------------------------------------------------------------------+ | + | | padding bytes to the next 8 byte alignment | | + | +---------------------------------------------------------------------+ | + | +---------------------------------------------------------------------+ | + | | Data Record | | + | | size: overall record size (without padding) | | + | | ... | | + | +---------------------------------------------------------------------+ | + | +---------------------------------------------------------------------+ | + | | padding bytes to the next 8 byte alignment | | + | +---------------------------------------------------------------------+ | + | +---------------------------------------------------------------------+ | + | | Data Record | | + | | size: overall record size | | + | | ... | | + | +---------------------------------------------------------------------+ | + | ... further data records ... | + +-------------------------------------------------------------------------+ + </programlisting> + </refsect1> + + <refsect1> + <title>Message payload</title> + + <para> + When connecting to the bus, receivers request a memory pool of a given + size, large enough to carry all backlog of data enqueued for the + connection. The pool is internally backed by a shared memory file which + can be <function>mmap()</function>ed by the receiver. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information. + </para> + + <para> + Message payload must be described in items attached to a message when + it is sent. A receiver can access the payload by looking at the items + that are attached to a message in its pool. The following items are used. + </para> + + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_PAYLOAD_VEC</constant></term> + <listitem> + <para> + This item references a piece of memory on the sender side which is + directly copied into the receiver's pool. This way, two peers can + exchange data by effectively doing a single-copy from one process + to another; the kernel will not buffer the data anywhere else. + This item is never found in a message received by a connection. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_PAYLOAD_OFF</constant></term> + <listitem> + <para> + This item is attached to messages on the receiving side and points + to a memory area inside the receiver's pool. The + <varname>offset</varname> variable in the item denotes the memory + location relative to the message itself. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_PAYLOAD_MEMFD</constant></term> + <listitem> + <para> + Messages can reference <emphasis>memfd</emphasis> files which + contain the data. memfd files are tmpfs-backed files that allow + sealing of the content of the file, which prevents all writable + access to the file content. + </para> + <para> + Only memfds that have + <constant>(F_SEAL_SHRINK|F_SEAL_GROW|F_SEAL_WRITE|F_SEAL_SEAL) + </constant> + set are accepted as payload data, which enforces reliable passing of + data. The receiver can assume that neither the sender nor anyone + else can alter the content after the message is sent. If those + seals are not set on the memfd, the ioctl will fail with + <errorcode>-1</errorcode>, and <varname>errno</varname> will be + set to <constant>ETXTBUSY</constant>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_FDS</constant></term> + <listitem> + <para> + Messages can transport regular file descriptors via + <constant>KDBUS_ITEM_FDS</constant>. This item carries an array + of <type>int</type> values in <varname>item.fd</varname>. The + maximum number of file descriptors in the item is + <constant>253</constant>, and only one item of this type is + accepted per message. All passed values must be valid file + descriptors; the open count of each file descriptors is increased + by installing it to the receiver's task. This item can only be + used for directed messages, not for broadcasts, and only to + remote peers that have opted-in for receiving file descriptors + at connection time (<constant>KDBUS_HELLO_ACCEPT_FD</constant>). + </para> + </listitem> + </varlistentry> + </variablelist> + + <para> + The sender must not make any assumptions on the type in which data is + received by the remote peer. The kernel is free to re-pack multiple + <constant>KDBUS_ITEM_PAYLOAD_VEC</constant> and + <constant>KDBUS_ITEM_PAYLOAD_MEMFD</constant> payloads. For instance, the + kernel may decide to merge multiple <constant>VECs</constant> into a + single <constant>VEC</constant>, inline <constant>MEMFD</constant> + payloads into memory, or merge all passed <constant>VECs</constant> into a + single <constant>MEMFD</constant>. However, the kernel preserves the order + of passed data. This means that the order of all <constant>VEC</constant> + and <constant>MEMFD</constant> items is not changed in respect to each + other. In other words: All passed <constant>VEC</constant> and + <constant>MEMFD</constant> data payloads are treated as a single stream + of data that may be received by the remote peer in a different set of + chunks than it was sent as. + </para> + </refsect1> + + <refsect1> + <title>Sending messages</title> + + <para> + Messages are passed to the kernel with the + <constant>KDBUS_CMD_SEND</constant> ioctl. Depending on the destination + address of the message, the kernel delivers the message to the specific + destination connection, or to some subset of all connections on the same + bus. Sending messages across buses is not possible. Messages are always + queued in the memory pool of the destination connection (see above). + </para> + + <para> + The <constant>KDBUS_CMD_SEND</constant> ioctl uses a + <type>struct kdbus_cmd_send</type> to describe the message + transfer. + </para> + <programlisting> +struct kdbus_cmd_send { + __u64 size; + __u64 flags; + __u64 return_flags; + __u64 msg_address; + struct kdbus_msg_info reply; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para>Flags for message delivery</para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_SEND_SYNC_REPLY</constant></term> + <listitem> + <para> + By default, all calls to kdbus are considered asynchronous, + non-blocking. However, as there are many use cases that need + to wait for a remote peer to answer a method call, there's a + way to send a message and wait for a reply in a synchronous + fashion. This is what the + <constant>KDBUS_SEND_SYNC_REPLY</constant> controls. The + <constant>KDBUS_CMD_SEND</constant> ioctl will block until the + reply has arrived, the timeout limit is reached, in case the + remote connection was shut down, or if interrupted by a signal + before any reply; see + <citerefentry> + <refentrytitle>signal</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + + The offset of the reply message in the sender's pool is stored + in in <varname>offset_reply</varname> when the ioctl has + returned without error. Hence, there is no need for another + <constant>KDBUS_CMD_RECV</constant> ioctl or anything else to + receive the reply. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_FLAG_NEGOTIATE</constant></term> + <listitem> + <para> + Request a set of valid flags for this ioctl. When this bit is + set, no action is taken; the ioctl will fail with + <errorcode>-1</errorcode>, <varname>errno</varname> + is set to <constant>EPROTO</constant>. + Once the ioctl returned, the <varname>flags</varname> + field will have all bits set that the kernel recognizes as + valid for this command. + The <constant>KDBUS_FLAG_NEGOTIATE</constant> bit will be + cleared by the operation. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>msg_address</varname></term> + <listitem><para> + In this field, users have to provide a pointer to a message + (<type>struct kdbus_msg</type>) to send. See below for a + detailed description. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>reply</varname></term> + <listitem><para> + Only used for synchronous replies. See description of + <type>struct kdbus_cmd_recv</type> for more details. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + The following items are currently recognized. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_CANCEL_FD</constant></term> + <listitem> + <para> + When this optional item is passed in, and the call is + executed as SYNC call, the passed in file descriptor can be + used as alternative cancellation point. The kernel will call + <citerefentry> + <refentrytitle>poll</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + on this file descriptor, and once it reports any incoming + bytes, the blocking send operation will be canceled; the + blocking, synchronous ioctl call will return + <errorcode>-1</errorcode>, and <varname>errno</varname> will + be set to <errorname>ECANCELED</errorname>. + Any type of file descriptor on which + <citerefentry> + <refentrytitle>poll</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + can be called on can be used as payload to this item; for + example, an eventfd can be used for this purpose, see + <citerefentry> + <refentrytitle>eventfd</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry>. + For asynchronous message sending, this item is allowed but + ignored. + </para> + </listitem> + </varlistentry> + </variablelist> + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <constant>EINVAL</constant>. + </para> + </listitem> + </varlistentry> + </variablelist> + + <para> + The fields in this struct are described below. + The message referenced the <varname>msg_address</varname> above has + the following layout. + </para> + + <programlisting> +struct kdbus_msg { + __u64 size; + __u64 flags; + __s64 priority; + __u64 dst_id; + __u64 src_id; + __u64 payload_type; + __u64 cookie; + __u64 timeout_ns; + __u64 cookie_reply; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para>Flags to describe message details.</para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_MSG_EXPECT_REPLY</constant></term> + <listitem> + <para> + Expect a reply to this message from the remote peer. With + this bit set, the timeout_ns field must be set to a non-zero + number of nanoseconds in which the receiving peer is expected + to reply. If such a reply is not received in time, the sender + will be notified with a timeout message (see below). The + value must be an absolute value, in nanoseconds and based on + <constant>CLOCK_MONOTONIC</constant>. + </para><para> + For a message to be accepted as reply, it must be a direct + message to the original sender (not a broadcast and not a + signal message), and its + <varname>kdbus_msg.reply_cookie</varname> must match the + previous message's <varname>kdbus_msg.cookie</varname>. + </para><para> + Expected replies also temporarily open the policy of the + sending connection, so the other peer is allowed to respond + within the given time window. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_MSG_NO_AUTO_START</constant></term> + <listitem> + <para> + By default, when a message is sent to an activator + connection, the activator is notified and will start an + implementer. This flag inhibits that behavior. With this bit + set, and the remote being an activator, the ioctl will fail + with <varname>errno</varname> set to + <constant>EADDRNOTAVAIL</constant>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_FLAG_NEGOTIATE</constant></term> + <listitem> + <para> + Requests a set of valid flags for this ioctl. When this bit is + set, no action is taken; the ioctl will return + <errorcode>0</errorcode>, and the <varname>flags</varname> + field will have all bits set that are valid for this command. + The <constant>KDBUS_FLAG_NEGOTIATE</constant> bit will be + cleared by the operation. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>priority</varname></term> + <listitem><para> + The priority of this message. Receiving messages (see below) may + optionally be constrained to messages of a minimal priority. This + allows for use cases where timing critical data is interleaved with + control data on the same connection. If unused, the priority field + should be set to <constant>0</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>dst_id</varname></term> + <listitem><para> + The numeric ID of the destination connection, or + <constant>KDBUS_DST_ID_BROADCAST</constant> + (~0ULL) to address every peer on the bus, or + <constant>KDBUS_DST_ID_NAME</constant> (0) to look + it up dynamically from the bus' name registry. + In the latter case, an item of type + <constant>KDBUS_ITEM_DST_NAME</constant> is mandatory. + Also see + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + . + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>src_id</varname></term> + <listitem><para> + Upon return of the ioctl, this member will contain the sending + connection's numerical ID. Should be 0 at send time. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>payload_type</varname></term> + <listitem><para> + Type of the payload in the actual data records. Currently, only + <constant>KDBUS_PAYLOAD_DBUS</constant> is accepted as input value + of this field. When receiving messages that are generated by the + kernel (notifications), this field will contain + <constant>KDBUS_PAYLOAD_KERNEL</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>cookie</varname></term> + <listitem><para> + Cookie of this message, for later recognition. Also, when replying + to a message (see above), the <varname>cookie_reply</varname> + field must match this value. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>timeout_ns</varname></term> + <listitem><para> + If the message sent requires a reply from the remote peer (see above), + this field contains the timeout in absolute nanoseconds based on + <constant>CLOCK_MONOTONIC</constant>. Also see + <citerefentry> + <refentrytitle>clock_gettime</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>cookie_reply</varname></term> + <listitem><para> + If the message sent is a reply to another message, this field must + match the cookie of the formerly received message. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + A dynamically sized list of items to contain additional information. + The following items are expected/valid: + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_ITEM_PAYLOAD_VEC</constant></term> + <term><constant>KDBUS_ITEM_PAYLOAD_MEMFD</constant></term> + <term><constant>KDBUS_ITEM_FDS</constant></term> + <listitem> + <para> + Actual data records containing the payload. See section + "Passing of Payload Data". + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_BLOOM_FILTER</constant></term> + <listitem> + <para> + Bloom filter for matches (see below). + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ITEM_DST_NAME</constant></term> + <listitem> + <para> + Well-known name to send this message to. Required if + <varname>dst_id</varname> is set to + <constant>KDBUS_DST_ID_NAME</constant>. + If a connection holding the given name can't be found, + the ioctl will fail with <varname>errno</varname> set to + <constant>ESRCH</constant> is returned. + </para> + <para> + For messages to a unique name (ID), this item is optional. If + present, the kernel will make sure the name owner matches the + given unique name. This allows programs to tie the message + sending to the condition that a name is currently owned by a + certain unique name. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + </variablelist> + + <para> + The message will be augmented by the requested metadata items when + queued into the receiver's pool. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + and + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on metadata. + </para> + </refsect1> + + <refsect1> + <title>Receiving messages</title> + + <para> + Messages are received by the client with the + <constant>KDBUS_CMD_RECV</constant> ioctl. The endpoint file of the bus + supports <function>poll()/epoll()/select()</function>; when new messages + are available on the connection's file descriptor, + <constant>POLLIN</constant> is reported. For compatibility reasons, + <constant>POLLOUT</constant> is always reported as well. Note, however, + that the latter does not guarantee that a message can in fact be sent, as + this depends on how many pending messages the receiver has in its pool. + </para> + + <para> + With the <constant>KDBUS_CMD_RECV</constant> ioctl, a + <type>struct kdbus_cmd_recv</type> is used. + </para> + + <programlisting> +struct kdbus_cmd_recv { + __u64 size; + __u64 flags; + __u64 return_flags; + __s64 priority; + __u64 dropped_msgs; + struct kdbus_msg_info msg; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para>Flags to control the receive command.</para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_RECV_PEEK</constant></term> + <listitem> + <para> + Just return the location of the next message. Do not install + file descriptors or anything else. This is usually used to + determine the sender of the next queued message. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_RECV_DROP</constant></term> + <listitem> + <para> + Drop the next message without doing anything else with it, + and free the pool slice. This a short-cut for + <constant>KDBUS_RECV_PEEK</constant> and + <constant>KDBUS_CMD_FREE</constant>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_RECV_USE_PRIORITY</constant></term> + <listitem> + <para> + Dequeue the messages ordered by their priority, and filtering + them with the priority field (see below). + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_FLAG_NEGOTIATE</constant></term> + <listitem> + <para> + Request a set of valid flags for this ioctl. When this bit is + set, no action is taken; the ioctl will fail with + <errorcode>-1</errorcode>, <varname>errno</varname> + is set to <constant>EPROTO</constant>. + Once the ioctl returned, the <varname>flags</varname> + field will have all bits set that the kernel recognizes as + valid for this command. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. If the <varname>dropped_msgs</varname> + field is non-zero, <constant>KDBUS_RECV_RETURN_DROPPED_MSGS</constant> + is set. If a file descriptor could not be installed, the + <constant>KDBUS_RECV_RETURN_INCOMPLETE_FDS</constant> flag is set. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>priority</varname></term> + <listitem><para> + With <constant>KDBUS_RECV_USE_PRIORITY</constant> set in + <varname>flags</varname>, messages will be dequeued ordered by their + priority, starting with the highest value. Also, messages will be + filtered by the value given in this field, so the returned message + will at least have the requested priority. If no such message is + waiting in the queue, the ioctl will fail, and + <varname>errno</varname> will be set to <constant>EAGAIN</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>dropped_msgs</varname></term> + <listitem><para> + Whenever a message with <constant>KDBUS_MSG_SIGNAL</constant> is sent + but cannot be queued on a peer (e.g., as it contains FDs but the peer + does not support FDs, or there is no space left in the peer's pool..) + the 'dropped_msgs' counter of the peer is incremented. On the next + RECV ioctl, the 'dropped_msgs' field is copied into the ioctl struct + and cleared on the peer. If it was non-zero, the + <constant>KDBUS_RECV_RETURN_DROPPED_MSGS</constant> flag will be set + in <varname>return_flags</varname>. Note that this will only happen + if the ioctl succeeded or failed with <constant>EAGAIN</constant>. In + other error cases, the 'dropped_msgs' field of the peer is left + untouched. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>msg</varname></term> + <listitem><para> + Embedded struct containing information on the received message when + this command succeeded (see below). + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem><para> + Items to specify further details for the receive command. + Currently unused, and all items will be rejected with + <varname>errno</varname> set to <constant>EINVAL</constant>. + </para></listitem> + </varlistentry> + </variablelist> + + <para> + Both <type>struct kdbus_cmd_recv</type> and + <type>struct kdbus_cmd_send</type> embed + <type>struct kdbus_msg_info</type>. + For the <constant>KDBUS_CMD_SEND</constant> ioctl, it is used to catch + synchronous replies, if one was requested, and is unused otherwise. + </para> + + <programlisting> +struct kdbus_msg_info { + __u64 offset; + __u64 msg_size; + __u64 return_flags; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>offset</varname></term> + <listitem><para> + Upon return of the ioctl, this field contains the offset in the + receiver's memory pool. The memory must be freed with + <constant>KDBUS_CMD_FREE</constant>. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for further details. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>msg_size</varname></term> + <listitem><para> + Upon successful return of the ioctl, this field contains the size of + the allocated slice at offset <varname>offset</varname>. + It is the combination of the size of the stored + <type>struct kdbus_msg</type> object plus all appended VECs. + You can use it in combination with <varname>offset</varname> to map + a single message, instead of mapping the entire pool. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for further details. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem> + <para> + Kernel-provided return flags. Currently, the following flags are + defined. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_RECV_RETURN_INCOMPLETE_FDS</constant></term> + <listitem> + <para> + The message contained memfds or file descriptors, and the + kernel failed to install one or more of them at receive time. + Most probably that happened because the maximum number of + file descriptors for the receiver's task were exceeded. + In such cases, the message is still delivered, so this is not + a fatal condition. File descriptors numbers inside the + <constant>KDBUS_ITEM_FDS</constant> item or memfd files + referenced by <constant>KDBUS_ITEM_PAYLOAD_MEMFD</constant> + items which could not be installed will be set to + <constant>-1</constant>. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + </variablelist> + + <para> + Unless <constant>KDBUS_RECV_DROP</constant> was passed, the + <varname>offset</varname> field contains the location of the new message + inside the receiver's pool after the <constant>KDBUS_CMD_RECV</constant> + ioctl was employed. The message is stored as <type>struct kdbus_msg</type> + at this offset, and can be interpreted with the semantics described above. + </para> + <para> + Also, if the connection allowed for file descriptor to be passed + (<constant>KDBUS_HELLO_ACCEPT_FD</constant>), and if the message contained + any, they will be installed into the receiving process when the + <constant>KDBUS_CMD_RECV</constant> ioctl is called. + <emphasis>memfds</emphasis> may always be part of the message payload. + The receiving task is obliged to close all file descriptors appropriately + once no longer needed. If <constant>KDBUS_RECV_PEEK</constant> is set, no + file descriptors are installed. This allows for peeking at a message, + looking at its metadata only and dropping it via + <constant>KDBUS_RECV_DROP</constant>, without installing any of the file + descriptors into the receiving process. + </para> + <para> + The caller is obliged to call the <constant>KDBUS_CMD_FREE</constant> + ioctl with the returned offset when the memory is no longer needed. + </para> + </refsect1> + + <refsect1> + <title>Notifications</title> + <para> + A kernel notification is a regular kdbus message with the following + details. + </para> + + <itemizedlist> + <listitem><para> + kdbus_msg.src_id == <constant>KDBUS_SRC_ID_KERNEL</constant> + </para></listitem> + <listitem><para> + kdbus_msg.dst_id == <constant>KDBUS_DST_ID_BROADCAST</constant> + </para></listitem> + <listitem><para> + kdbus_msg.payload_type == <constant>KDBUS_PAYLOAD_KERNEL</constant> + </para></listitem> + <listitem><para> + Has exactly one of the items attached that are described below. + </para></listitem> + <listitem><para> + Always has a timestamp item (<constant>KDBUS_ITEM_TIMESTAMP</constant>) + attached. + </para></listitem> + </itemizedlist> + + <para> + The kernel will notify its users of the following events. + </para> + + <itemizedlist> + <listitem><para> + When connection <emphasis>A</emphasis> is terminated while connection + <emphasis>B</emphasis> is waiting for a reply from it, connection + <emphasis>B</emphasis> is notified with a message with an item of + type <constant>KDBUS_ITEM_REPLY_DEAD</constant>. + </para></listitem> + + <listitem><para> + When connection <emphasis>A</emphasis> does not receive a reply from + connection <emphasis>B</emphasis> within the specified timeout window, + connection <emphasis>A</emphasis> will receive a message with an + item of type <constant>KDBUS_ITEM_REPLY_TIMEOUT</constant>. + </para></listitem> + + <listitem><para> + When an ordinary connection (not a monitor) is created on or removed + from a bus, messages with an item of type + <constant>KDBUS_ITEM_ID_ADD</constant> or + <constant>KDBUS_ITEM_ID_REMOVE</constant>, respectively, are delivered + to all bus members that match these messages through their match + database. Eavesdroppers (monitor connections) do not cause such + notifications to be sent. They are invisible on the bus. + </para></listitem> + + <listitem><para> + When a connection gains or loses ownership of a name, messages with an + item of type <constant>KDBUS_ITEM_NAME_ADD</constant>, + <constant>KDBUS_ITEM_NAME_REMOVE</constant> or + <constant>KDBUS_ITEM_NAME_CHANGE</constant> are delivered to all bus + members that match these messages through their match database. + </para></listitem> + </itemizedlist> + </refsect1> + + <refsect1> + <title>Return value</title> + <para> + On success, all mentioned ioctl commands return <errorcode>0</errorcode>; + on error, <errorcode>-1</errorcode> is returned, and + <varname>errno</varname> is set to indicate the error. + If the issued ioctl is illegal for the file descriptor used, + <varname>errno</varname> will be set to <constant>ENOTTY</constant>. + </para> + + <refsect2> + <title> + <constant>KDBUS_CMD_SEND</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EOPNOTSUPP</constant></term> + <listitem><para> + The connection is not an ordinary connection, or the passed + file descriptors in <constant>KDBUS_ITEM_FDS</constant> item are + either kdbus handles or unix domain sockets. Both are currently + unsupported. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + The submitted payload type is + <constant>KDBUS_PAYLOAD_KERNEL</constant>, + <constant>KDBUS_MSG_EXPECT_REPLY</constant> was set without timeout + or cookie values, <constant>KDBUS_SEND_SYNC_REPLY</constant> was + set without <constant>KDBUS_MSG_EXPECT_REPLY</constant>, an invalid + item was supplied, <constant>src_id</constant> was non-zero and was + different from the current connection's ID, a supplied memfd had a + size of 0, or a string was not properly null-terminated. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ENOTUNIQ</constant></term> + <listitem><para> + The supplied destination is + <constant>KDBUS_DST_ID_BROADCAST</constant> and either + file descriptors were passed, or + <constant>KDBUS_MSG_EXPECT_REPLY</constant> was set, + or a timeout was given. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>E2BIG</constant></term> + <listitem><para> + Too many items + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EMSGSIZE</constant></term> + <listitem><para> + The size of the message header and items or the payload vector + is excessive. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EEXIST</constant></term> + <listitem><para> + Multiple <constant>KDBUS_ITEM_FDS</constant>, + <constant>KDBUS_ITEM_BLOOM_FILTER</constant> or + <constant>KDBUS_ITEM_DST_NAME</constant> items were supplied. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EBADF</constant></term> + <listitem><para> + The supplied <constant>KDBUS_ITEM_FDS</constant> or + <constant>KDBUS_ITEM_PAYLOAD_MEMFD</constant> items + contained an illegal file descriptor. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EMEDIUMTYPE</constant></term> + <listitem><para> + The supplied memfd is not a sealed kdbus memfd. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EMFILE</constant></term> + <listitem><para> + Too many file descriptors inside a + <constant>KDBUS_ITEM_FDS</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EBADMSG</constant></term> + <listitem><para> + An item had illegal size, both a <constant>dst_id</constant> and a + <constant>KDBUS_ITEM_DST_NAME</constant> was given, or both a name + and a bloom filter was given. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ETXTBSY</constant></term> + <listitem><para> + The supplied kdbus memfd file cannot be sealed or the seal + was removed, because it is shared with other processes or + still mapped with + <citerefentry> + <refentrytitle>mmap</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ECOMM</constant></term> + <listitem><para> + A peer does not accept the file descriptors addressed to it. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EFAULT</constant></term> + <listitem><para> + The supplied bloom filter size was not 64-bit aligned, or supplied + memory could not be accessed by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EDOM</constant></term> + <listitem><para> + The supplied bloom filter size did not match the bloom filter + size of the bus. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EDESTADDRREQ</constant></term> + <listitem><para> + <constant>dst_id</constant> was set to + <constant>KDBUS_DST_ID_NAME</constant>, but no + <constant>KDBUS_ITEM_DST_NAME</constant> was attached. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ESRCH</constant></term> + <listitem><para> + The name to look up was not found in the name registry. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EADDRNOTAVAIL</constant></term> + <listitem><para> + <constant>KDBUS_MSG_NO_AUTO_START</constant> was given but the + destination connection is an activator. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ENXIO</constant></term> + <listitem><para> + The passed numeric destination connection ID couldn't be found, + or is not connected. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ECONNRESET</constant></term> + <listitem><para> + The destination connection is no longer active. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ETIMEDOUT</constant></term> + <listitem><para> + Timeout while synchronously waiting for a reply. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINTR</constant></term> + <listitem><para> + Interrupted system call while synchronously waiting for a reply. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EPIPE</constant></term> + <listitem><para> + When sending a message, a synchronous reply from the receiving + connection was expected but the connection died before answering. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ENOBUFS</constant></term> + <listitem><para> + Too many pending messages on the receiver side. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EREMCHG</constant></term> + <listitem><para> + Both a well-known name and a unique name (ID) was given, but + the name is not currently owned by that connection. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EXFULL</constant></term> + <listitem><para> + The memory pool of the receiver is full. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EREMOTEIO</constant></term> + <listitem><para> + While synchronously waiting for a reply, the remote peer + failed with an I/O error. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title> + <constant>KDBUS_CMD_RECV</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EOPNOTSUPP</constant></term> + <listitem><para> + The connection is not an ordinary connection, or the passed + file descriptors are either kdbus handles or unix domain + sockets. Both are currently unsupported. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Invalid flags or offset. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EAGAIN</constant></term> + <listitem><para> + No message found in the queue + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>clock_gettime</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>ioctl</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>poll</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>select</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>epoll</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>eventfd</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>memfd_create</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + </simplelist> + </refsect1> +</refentry> diff --git a/Documentation/kdbus/kdbus.name.xml b/Documentation/kdbus/kdbus.name.xml new file mode 100644 index 00000000000..3f5f6a6c5ed --- /dev/null +++ b/Documentation/kdbus/kdbus.name.xml @@ -0,0 +1,711 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus.name"> + + <refentryinfo> + <title>kdbus.name</title> + <productname>kdbus.name</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus.name</refname> + <refpurpose>kdbus.name</refpurpose> + </refnamediv> + + <refsect1> + <title>Description</title> + <para> + Each + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + instantiates a name registry to resolve well-known names into unique + connection IDs for message delivery. The registry will be queried when a + message is sent with <varname>kdbus_msg.dst_id</varname> set to + <constant>KDBUS_DST_ID_NAME</constant>, or when a registry dump is + requested with <constant>KDBUS_CMD_NAME_LIST</constant>. + </para> + + <para> + All of the below is subject to policy rules for <emphasis>SEE</emphasis> + and <emphasis>OWN</emphasis> permissions. See + <citerefentry> + <refentrytitle>kdbus.policy</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information. + </para> + </refsect1> + + <refsect1> + <title>Name validity</title> + <para> + A name has to comply with the following rules in order to be considered + valid. + </para> + + <itemizedlist> + <listitem> + <para> + The name has two or more elements separated by a + '<literal>.</literal>' (period) character. + </para> + </listitem> + <listitem> + <para> + All elements must contain at least one character. + </para> + </listitem> + <listitem> + <para> + Each element must only contain the ASCII characters + <literal>[A-Z][a-z][0-9]_</literal> and must not begin with a + digit. + </para> + </listitem> + <listitem> + <para> + The name must contain at least one '<literal>.</literal>' (period) + character (and thus at least two elements). + </para> + </listitem> + <listitem> + <para> + The name must not begin with a '<literal>.</literal>' (period) + character. + </para> + </listitem> + <listitem> + <para> + The name must not exceed <constant>255</constant> characters in + length. + </para> + </listitem> + </itemizedlist> + </refsect1> + + <refsect1> + <title>Acquiring a name</title> + <para> + To acquire a name, a client uses the + <constant>KDBUS_CMD_NAME_ACQUIRE</constant> ioctl with + <type>struct kdbus_cmd</type> as argument. + </para> + + <programlisting> +struct kdbus_cmd { + __u64 size; + __u64 flags; + __u64 return_flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para>Flags to control details in the name acquisition.</para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_NAME_REPLACE_EXISTING</constant></term> + <listitem> + <para> + Acquiring a name that is already present usually fails, + unless this flag is set in the call, and + <constant>KDBUS_NAME_ALLOW_REPLACEMENT</constant> (see below) + was set when the current owner of the name acquired it, or + if the current owner is an activator connection (see + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>). + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_NAME_ALLOW_REPLACEMENT</constant></term> + <listitem> + <para> + Allow other connections to take over this name. When this + happens, the former owner of the connection will be notified + of the name loss. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_NAME_QUEUE</constant></term> + <listitem> + <para> + A name that is already acquired by a connection can not be + acquired again (unless the + <constant>KDBUS_NAME_ALLOW_REPLACEMENT</constant> flag was + set during acquisition; see above). + However, a connection can put itself in a queue of + connections waiting for the name to be released. Once that + happens, the first connection in that queue becomes the new + owner and is notified accordingly. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_FLAG_NEGOTIATE</constant></term> + <listitem> + <para> + Request a set of valid flags for this ioctl. When this bit is + set, no action is taken; the ioctl will fail with + <errorcode>-1</errorcode>, and <varname>errno</varname> + is set to <constant>EPROTO</constant>. + Once the ioctl returned, the <varname>flags</varname> + field will have all bits set that the kernel recognizes as + valid for this command. + The <constant>KDBUS_FLAG_NEGOTIATE</constant> bit will be + cleared by the operation. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem> + <para> + Flags returned by the kernel. Currently, the following may be + returned by the kernel. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_NAME_IN_QUEUE</constant></term> + <listitem> + <para> + The name was not acquired yet, but the connection was + placed in the queue of peers waiting for the name. + This can only happen if <constant>KDBUS_NAME_QUEUE</constant> + was set in the <varname>flags</varname> member (see above). + The connection will receive a name owner change notification + once the current owner has given up the name and its + ownership was transferred. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + Items to submit the name. Currently, one item of type + <constant>KDBUS_ITEM_NAME</constant> is expected and allowed, and + the contained string must be a valid bus name. + <constant>KDBUS_ITEM_NEGOTIATE</constant> may be used to probe for + valid item types. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for a detailed description of how this item is used. + </para> + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <errorname>>EINVAL</errorname>. + </para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Releasing a name</title> + <para> + A connection may release a name explicitly with the + <constant>KDBUS_CMD_NAME_RELEASE</constant> ioctl. If the connection was + an implementer of an activatable name, its pending messages are moved + back to the activator. If there are any connections queued up as waiters + for the name, the first one in the queue (the oldest entry) will become + the new owner. The same happens implicitly for all names once a + connection terminates. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on connections. + </para> + <para> + The <constant>KDBUS_CMD_NAME_RELEASE</constant> ioctl uses the same data + structure as the acquisition call + (<constant>KDBUS_CMD_NAME_ACQUIRE</constant>), + but with slightly different field usage. + </para> + + <programlisting> +struct kdbus_cmd { + __u64 size; + __u64 flags; + __u64 return_flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para> + Flags to the command. Currently unused. + <constant>KDBUS_FLAG_NEGOTIATE</constant> is accepted to probe for + valid flags. If set, the ioctl will return <errorcode>0</errorcode>, + and the <varname>flags</varname> field is set to + <constant>0</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + Items to submit the name. Currently, one item of type + <constant>KDBUS_ITEM_NAME</constant> is expected and allowed, and + the contained string must be a valid bus name. + <constant>KDBUS_ITEM_NEGOTIATE</constant> may be used to probe for + valid item types. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for a detailed description of how this item is used. + </para> + <para> + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <constant>EINVAL</constant>. + </para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Dumping the name registry</title> + <para> + A connection may request a complete or filtered dump of currently active + bus names with the <constant>KDBUS_CMD_LIST</constant> ioctl, which + takes a <type>struct kdbus_cmd_list</type> as argument. + </para> + + <programlisting> +struct kdbus_cmd_list { + __u64 flags; + __u64 return_flags; + __u64 offset; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>flags</varname></term> + <listitem> + <para> + Any combination of flags to specify which names should be dumped. + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_LIST_UNIQUE</constant></term> + <listitem> + <para> + List the unique (numeric) IDs of the connection, whether it + owns a name or not. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_LIST_NAMES</constant></term> + <listitem> + <para> + List well-known names stored in the database which are + actively owned by a real connection (not an activator). + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_LIST_ACTIVATORS</constant></term> + <listitem> + <para> + List names that are owned by an activator. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_LIST_QUEUED</constant></term> + <listitem> + <para> + List connections that are not yet owning a name but are + waiting for it to become available. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_FLAG_NEGOTIATE</constant></term> + <listitem> + <para> + Request a set of valid flags for this ioctl. When this bit is + set, no action is taken; the ioctl will fail with + <errorcode>-1</errorcode>, and <varname>errno</varname> + is set to <constant>EPROTO</constant>. + Once the ioctl returned, the <varname>flags</varname> + field will have all bits set that the kernel recognizes as + valid for this command. + The <constant>KDBUS_FLAG_NEGOTIATE</constant> bit will be + cleared by the operation. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>offset</varname></term> + <listitem><para> + When the ioctl returns successfully, the offset to the name registry + dump inside the connection's pool will be stored in this field. + </para></listitem> + </varlistentry> + </variablelist> + + <para> + The returned list of names is stored in a <type>struct kdbus_list</type> + that in turn contains an array of type <type>struct kdbus_info</type>, + The array-size in bytes is given as <varname>list_size</varname>. + The fields inside <type>struct kdbus_info</type> is described next. + </para> + + <programlisting> +struct kdbus_info { + __u64 size; + __u64 id; + __u64 flags; + struct kdbus_item items[0]; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>id</varname></term> + <listitem><para> + The owning connection's unique ID. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para> + The flags of the owning connection. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem> + <para> + Items containing the actual name. Currently, one item of type + <constant>KDBUS_ITEM_OWNED_NAME</constant> will be attached, + including the name's flags. In that item, the flags field of the + name may carry the following bits: + </para> + <variablelist> + <varlistentry> + <term><constant>KDBUS_NAME_ALLOW_REPLACEMENT</constant></term> + <listitem> + <para> + Other connections are allowed to take over this name from the + connection that owns it. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_NAME_IN_QUEUE</constant></term> + <listitem> + <para> + When retrieving a list of currently acquired names in the + registry, this flag indicates whether the connection + actually owns the name or is currently waiting for it to + become available. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_NAME_ACTIVATOR</constant></term> + <listitem> + <para> + An activator connection owns a name as a placeholder for an + implementer, which is started on demand by programs as soon + as the first message arrives. There's some more information + on this topic in + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + . + </para> + <para> + In contrast to + <constant>KDBUS_NAME_REPLACE_EXISTING</constant>, + when a name is taken over from an activator connection, all + the messages that have been queued in the activator + connection will be moved over to the new owner. The activator + connection will still be tracked for the name and will take + control again if the implementer connection terminates. + </para> + <para> + This flag can not be used when acquiring a name, but is + implicitly set through <constant>KDBUS_CMD_HELLO</constant> + with <constant>KDBUS_HELLO_ACTIVATOR</constant> set in + <varname>kdbus_cmd_hello.conn_flags</varname>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_FLAG_NEGOTIATE</constant></term> + <listitem> + <para> + Requests a set of valid flags for this ioctl. When this bit is + set, no action is taken; the ioctl will return + <errorcode>0</errorcode>, and the <varname>flags</varname> + field will have all bits set that are valid for this command. + The <constant>KDBUS_FLAG_NEGOTIATE</constant> bit will be + cleared by the operation. + </para> + </listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + </variablelist> + + <para> + The returned buffer must be freed with the + <constant>KDBUS_CMD_FREE</constant> ioctl when the user is finished with + it. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information. + </para> + </refsect1> + + <refsect1> + <title>Return value</title> + <para> + On success, all mentioned ioctl commands return <errorcode>0</errorcode>; + on error, <errorcode>-1</errorcode> is returned, and + <varname>errno</varname> is set to indicate the error. + If the issued ioctl is illegal for the file descriptor used, + <varname>errno</varname> will be set to <constant>ENOTTY</constant>. + </para> + + <refsect2> + <title> + <constant>KDBUS_CMD_NAME_ACQUIRE</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Illegal command flags, illegal name provided, or an activator + tried to acquire a second name. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EPERM</constant></term> + <listitem><para> + Policy prohibited name ownership. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EALREADY</constant></term> + <listitem><para> + Connection already owns that name. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EEXIST</constant></term> + <listitem><para> + The name already exists and can not be taken over. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>E2BIG</constant></term> + <listitem><para> + The maximum number of well-known names per connection is exhausted. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title> + <constant>KDBUS_CMD_NAME_RELEASE</constant> + may fail with the following errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Invalid command flags, or invalid name provided. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ESRCH</constant></term> + <listitem><para> + Name is not found in the registry. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EADDRINUSE</constant></term> + <listitem><para> + Name is owned by a different connection and can't be released. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title> + <constant>KDBUS_CMD_LIST</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Invalid command flags + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>ENOBUFS</constant></term> + <listitem><para> + No available memory in the connection's pool. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.policy</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + </simplelist> + </refsect1> +</refentry> diff --git a/Documentation/kdbus/kdbus.policy.xml b/Documentation/kdbus/kdbus.policy.xml new file mode 100644 index 00000000000..67324163880 --- /dev/null +++ b/Documentation/kdbus/kdbus.policy.xml @@ -0,0 +1,406 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus.policy"> + + <refentryinfo> + <title>kdbus.policy</title> + <productname>kdbus.policy</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus.policy</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus.policy</refname> + <refpurpose>kdbus policy</refpurpose> + </refnamediv> + + <refsect1> + <title>Description</title> + + <para> + A kdbus policy restricts the possibilities of connections to own, see and + talk to well-known names. A policy can be associated with a bus (through a + policy holder connection) or a custom endpoint. kdbus stores its policy + information in a database that can be accessed through the following + ioctl commands: + </para> + + <variablelist> + <varlistentry> + <term><constant>KDBUS_CMD_HELLO</constant></term> + <listitem><para> + When creating, or updating, a policy holder connection. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_CMD_ENDPOINT_MAKE</constant></term> + <term><constant>KDBUS_CMD_ENDPOINT_UPDATE</constant></term> + <listitem><para> + When creating, or updating, a bus custom endpoint. See + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + </varlistentry> + </variablelist> + + <para> + In all cases, the name and policy access information is stored in items + of type <constant>KDBUS_ITEM_NAME</constant> and + <constant>KDBUS_ITEM_POLICY_ACCESS</constant>. For this transport, the + following rules apply. + </para> + + <itemizedlist> + <listitem> + <para> + An item of type <constant>KDBUS_ITEM_NAME</constant> must be followed + by at least one <constant>KDBUS_ITEM_POLICY_ACCESS</constant> item. + </para> + </listitem> + + <listitem> + <para> + An item of type <constant>KDBUS_ITEM_NAME</constant> can be followed + by an arbitrary number of + <constant>KDBUS_ITEM_POLICY_ACCESS</constant> items. + </para> + </listitem> + + <listitem> + <para> + An arbitrary number of groups of names and access levels can be given. + </para> + </listitem> + </itemizedlist> + + <para> + Names passed in items of type <constant>KDBUS_ITEM_NAME</constant> must + comply to the rules of valid kdbus.name. See + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information. + + The payload of an item of type + <constant>KDBUS_ITEM_POLICY_ACCESS</constant> is defined by the following + struct. For more information on the layout of items, please refer to + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para> + + <programlisting> +struct kdbus_policy_access { + __u64 type; + __u64 access; + __u64 id; +}; + </programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>type</varname></term> + <listitem> + <para> + One of the following. + </para> + + <variablelist> + <varlistentry> + <term><constant>KDBUS_POLICY_ACCESS_USER</constant></term> + <listitem><para> + Grant access to a user with the UID stored in the + <varname>id</varname> field. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_POLICY_ACCESS_GROUP</constant></term> + <listitem><para> + Grant access to a user with the GID stored in the + <varname>id</varname> field. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_POLICY_ACCESS_WORLD</constant></term> + <listitem><para> + Grant access to everyone. The <varname>id</varname> field + is ignored. + </para></listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>access</varname></term> + <listitem> + <para> + The access to grant. One of the following. + </para> + + <variablelist> + <varlistentry> + <term><constant>KDBUS_POLICY_SEE</constant></term> + <listitem><para> + Allow the name to be seen. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_POLICY_TALK</constant></term> + <listitem><para> + Allow the name to be talked to. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_POLICY_OWN</constant></term> + <listitem><para> + Allow the name to be owned. + </para></listitem> + </varlistentry> + </variablelist> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>id</varname></term> + <listitem><para> + For <constant>KDBUS_POLICY_ACCESS_USER</constant>, stores the UID. + For <constant>KDBUS_POLICY_ACCESS_GROUP</constant>, stores the GID. + </para></listitem> + </varlistentry> + + </variablelist> + + <para> + All endpoints of buses have an empty policy database by default. + Therefore, unless policy rules are added, all operations will also be + denied by default. Also see + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para> + </refsect1> + + <refsect1> + <title>Wildcard names</title> + <para> + Policy holder connections may upload names that contain the wildcard + suffix (<literal>".*"</literal>). Such a policy entry is effective for + every well-known name that extends the provided name by exactly one more + level. + + For example, the name <literal>foo.bar.*</literal> matches both + <literal>"foo.bar.baz"</literal> and + <literal>"foo.bar.bazbaz"</literal> are, but not + <literal>"foo.bar.baz.baz"</literal>. + + This allows connections to take control over multiple names that the + policy holder doesn't need to know about when uploading the policy. + + Such wildcard entries are not allowed for custom endpoints. + </para> + </refsect1> + + <refsect1> + <title>Privileged connections</title> + <para> + The policy database is overruled when action is taken by a privileged + connection. Please refer to + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information on what makes a connection privileged. + </para> + </refsect1> + + <refsect1> + <title>Examples</title> + <para> + For instance, a set of policy rules may look like this: + </para> + + <programlisting> +KDBUS_ITEM_NAME: str='org.foo.bar' +KDBUS_ITEM_POLICY_ACCESS: type=USER, access=OWN, ID=1000 +KDBUS_ITEM_POLICY_ACCESS: type=USER, access=TALK, ID=1001 +KDBUS_ITEM_POLICY_ACCESS: type=WORLD, access=SEE + +KDBUS_ITEM_NAME: str='org.blah.baz' +KDBUS_ITEM_POLICY_ACCESS: type=USER, access=OWN, ID=0 +KDBUS_ITEM_POLICY_ACCESS: type=WORLD, access=TALK + </programlisting> + + <para> + That means that 'org.foo.bar' may only be owned by UID 1000, but every + user on the bus is allowed to see the name. However, only UID 1001 may + actually send a message to the connection and receive a reply from it. + + The second rule allows 'org.blah.baz' to be owned by UID 0 only, but + every user may talk to it. + </para> + </refsect1> + + <refsect1> + <title>TALK access and multiple well-known names per connection</title> + <para> + Note that TALK access is checked against all names of a connection. For + example, if a connection owns both <constant>'org.foo.bar'</constant> and + <constant>'org.blah.baz'</constant>, and the policy database allows + <constant>'org.blah.baz'</constant> to be talked to by WORLD, then this + permission is also granted to <constant>'org.foo.bar'</constant>. That + might sound illogical, but after all, we allow messages to be directed to + either the ID or a well-known name, and policy is applied to the + connection, not the name. In other words, the effective TALK policy for a + connection is the most permissive of all names the connection owns. + + For broadcast messages, the receiver needs TALK permissions to the sender + to receive the broadcast. + </para> + <para> + Both the endpoint and the bus policy databases are consulted to allow + name registry listing, owning a well-known name and message delivery. + If either one fails, the operation is failed with + <varname>errno</varname> set to <constant>EPERM</constant>. + + For best practices, connections that own names with a restricted TALK + access should not install matches. This avoids cases where the sent + message may pass the bloom filter due to false-positives and may also + satisfy the policy rules. + + Also see + <citerefentry> + <refentrytitle>kdbus.match</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para> + </refsect1> + + <refsect1> + <title>Implicit policies</title> + <para> + Depending on the type of the endpoint, a set of implicit rules that + override installed policies might be enforced. + + On default endpoints, the following set is enforced and checked before + any user-supplied policy is checked. + </para> + + <itemizedlist> + <listitem> + <para> + Privileged connections always override any installed policy. Those + connections could easily install their own policies, so there is no + reason to enforce installed policies. + </para> + </listitem> + <listitem> + <para> + Connections can always talk to connections of the same user. This + includes broadcast messages. + </para> + </listitem> + </itemizedlist> + + <para> + Custom endpoints have stricter policies. The following rules apply: + </para> + + <itemizedlist> + <listitem> + <para> + Policy rules are always enforced, even if the connection is a + privileged connection. + </para> + </listitem> + <listitem> + <para> + Policy rules are always enforced for <constant>TALK</constant> access, + even if both ends are running under the same user. This includes + broadcast messages. + </para> + </listitem> + <listitem> + <para> + To restrict the set of names that can be seen, endpoint policies can + install <constant>SEE</constant> policies. + </para> + </listitem> + </itemizedlist> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + </simplelist> + </refsect1> +</refentry> diff --git a/Documentation/kdbus/kdbus.pool.xml b/Documentation/kdbus/kdbus.pool.xml new file mode 100644 index 00000000000..05fd01902ad --- /dev/null +++ b/Documentation/kdbus/kdbus.pool.xml @@ -0,0 +1,320 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus.pool"> + + <refentryinfo> + <title>kdbus.pool</title> + <productname>kdbus.pool</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus.pool</refname> + <refpurpose>kdbus pool</refpurpose> + </refnamediv> + + <refsect1> + <title>Description</title> + <para> + A pool for data received from the kernel is installed for every + <emphasis>connection</emphasis> of the <emphasis>bus</emphasis>, and + is sized according to the information stored in the + <varname>pool_size</varname> member of <type>struct kdbus_cmd_hello</type> + when <constant>KDBUS_CMD_HELLO</constant> is employed. Internally, the + pool is segmented into <emphasis>slices</emphasis>, each referenced by its + <emphasis>offset</emphasis> in the pool, expressed in <type>bytes</type>. + See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more information about <constant>KDBUS_CMD_HELLO</constant>. + </para> + + <para> + The pool is written to by the kernel when one of the following + <emphasis>ioctls</emphasis> is issued: + + <variablelist> + <varlistentry> + <term><constant>KDBUS_CMD_HELLO</constant></term> + <listitem><para> + ... to receive details about the bus the connection was made to + </para></listitem> + </varlistentry> + <varlistentry> + <term><constant>KDBUS_CMD_RECV</constant></term> + <listitem><para> + ... to receive a message + </para></listitem> + </varlistentry> + <varlistentry> + <term><constant>KDBUS_CMD_LIST</constant></term> + <listitem><para> + ... to dump the name registry + </para></listitem> + </varlistentry> + <varlistentry> + <term><constant>KDBUS_CMD_CONN_INFO</constant></term> + <listitem><para> + ... to retrieve information on a connection + </para></listitem> + </varlistentry> + </variablelist> + + </para> + <para> + The <varname>offset</varname> fields returned by either one of the + aforementioned ioctls describe offsets inside the pool. In order to make + the slice available for subsequent calls, + <constant>KDBUS_CMD_FREE</constant> has to be called on that offset + (see below). Otherwise, the pool will fill up, and the connection won't + be able to receive any more information through its pool. + </para> + </refsect1> + + <refsect1> + <title>Pool slice allocation</title> + <para> + Pool slices are allocated by the kernel in order to report information + back to a task, such as messages, returned name list etc. + Allocation of pool slices cannot be initiated by userspace. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + and + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for examples of commands that use the <emphasis>pool</emphasis> to + return data. + </para> + </refsect1> + + <refsect1> + <title>Accessing the pool memory</title> + <para> + Memory in the pool is read-only for userspace and may only be written + to by the kernel. To read from the pool memory, the caller is expected to + <citerefentry> + <refentrytitle>mmap</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + the buffer into its task, like this: + </para> + <programlisting> +uint8_t *buf = mmap(NULL, size, PROT_READ, MAP_SHARED, conn_fd, 0); + </programlisting> + + <para> + In order to map the entire pool, the <varname>size</varname> parameter in + the example above should be set to the value of the + <varname>pool_size</varname> member of + <type>struct kdbus_cmd_hello</type> when + <constant>KDBUS_CMD_HELLO</constant> was employed to create the + connection (see above). + </para> + + <para> + The <emphasis>file descriptor</emphasis> used to map the memory must be + the one that was used to create the <emphasis>connection</emphasis>. + In other words, the one that was used to call + <constant>KDBUS_CMD_HELLO</constant>. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + + <para> + Alternatively, instead of mapping the entire pool buffer, only parts + of it can be mapped. Every kdbus command that returns an + <emphasis>offset</emphasis> (see above) also reports a + <emphasis>size</emphasis> along with it, so programs can be written + in a way that it only maps portions of the pool to access a specific + <emphasis>slice</emphasis>. + </para> + + <para> + When access to the pool memory is no longer needed, programs should + call <function>munmap()</function> on the pointer returned by + <function>mmap()</function>. + </para> + </refsect1> + + <refsect1> + <title>Freeing pool slices</title> + <para> + The <constant>KDBUS_CMD_FREE</constant> ioctl is used to free a slice + inside the pool, describing an offset that was returned in an + <varname>offset</varname> field of another ioctl struct. + The <constant>KDBUS_CMD_FREE</constant> command takes a + <type>struct kdbus_cmd_free</type> as argument. + </para> + +<programlisting> +struct kdbus_cmd_free { + __u64 size; + __u64 flags; + __u64 return_flags; + __u64 offset; + struct kdbus_item items[0]; +}; +</programlisting> + + <para>The fields in this struct are described below.</para> + + <variablelist> + <varlistentry> + <term><varname>size</varname></term> + <listitem><para> + The overall size of the struct, including its items. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>flags</varname></term> + <listitem><para> + Currently unused. + <constant>KDBUS_FLAG_NEGOTIATE</constant> is accepted to probe for + valid flags. If set, the ioctl will return <errorcode>0</errorcode>, + and the <varname>flags</varname> field is set to + <constant>0</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>return_flags</varname></term> + <listitem><para> + Flags returned by the kernel. Currently unused and always set to + <constant>0</constant> by the kernel. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>offset</varname></term> + <listitem><para> + The offset to free, as returned by other ioctls that allocated + memory for returned information. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>items</varname></term> + <listitem><para> + Items to specify further details for the receive command. + Currently unused. + Unrecognized items are rejected, and the ioctl will fail with + <varname>errno</varname> set to <constant>EINVAL</constant>. + All items except for + <constant>KDBUS_ITEM_NEGOTIATE</constant> (see + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + ) will be rejected. + </para></listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Return value</title> + <para> + On success, all mentioned ioctl commands return <errorcode>0</errorcode>; + on error, <errorcode>-1</errorcode> is returned, and + <varname>errno</varname> is set to indicate the error. + If the issued ioctl is illegal for the file descriptor used, + <varname>errno</varname> will be set to <constant>ENOTTY</constant>. + </para> + + <refsect2> + <title> + <constant>KDBUS_CMD_FREE</constant> may fail with the following + errors + </title> + + <variablelist> + <varlistentry> + <term><constant>ENXIO</constant></term> + <listitem><para> + No pool slice found at given offset. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + Invalid flags provided. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>EINVAL</constant></term> + <listitem><para> + The offset is valid, but the user is not allowed to free the slice. + This happens, for example, if the offset was retrieved with + <constant>KDBUS_RECV_PEEK</constant>. + </para></listitem> + </varlistentry> + </variablelist> + </refsect2> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>mmap</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>munmap</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + </simplelist> + </refsect1> +</refentry> diff --git a/Documentation/kdbus/kdbus.xml b/Documentation/kdbus/kdbus.xml new file mode 100644 index 00000000000..194abd2e76c --- /dev/null +++ b/Documentation/kdbus/kdbus.xml @@ -0,0 +1,1012 @@ +<?xml version='1.0'?> <!--*-nxml-*--> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<refentry id="kdbus"> + + <refentryinfo> + <title>kdbus</title> + <productname>kdbus</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>kdbus</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>kdbus</refname> + <refpurpose>Kernel Message Bus</refpurpose> + </refnamediv> + + <refsect1> + <title>Synopsis</title> + <para> + kdbus is an inter-process communication bus system controlled by the + kernel. It provides user-space with an API to create buses and send + unicast and multicast messages to one, or many, peers connected to the + same bus. It does not enforce any layout on the transmitted data, but + only provides the transport layer used for message interchange between + peers. + </para> + <para> + This set of man-pages gives a comprehensive overview of the kernel-level + API, with all ioctl commands, associated structs and bit masks. However, + most people will not use this API level directly, but rather let one of + the high-level abstraction libraries help them integrate D-Bus + functionality into their applications. + </para> + </refsect1> + + <refsect1> + <title>Description</title> + <para> + kdbus provides a pseudo filesystem called <emphasis>kdbusfs</emphasis>, + which is usually mounted on <filename>/sys/fs/kdbus</filename>. Bus + primitives can be accessed as files and sub-directories underneath this + mount-point. Any advanced operations are done via + <function>ioctl()</function> on files created by + <emphasis>kdbusfs</emphasis>. Multiple mount-points of + <emphasis>kdbusfs</emphasis> are independent of each other. This allows + namespacing of kdbus by mounting a new instance of + <emphasis>kdbusfs</emphasis> in a new mount-namespace. kdbus calls these + mount instances domains and each bus belongs to exactly one domain. + </para> + + <para> + kdbus was designed as a transport layer for D-Bus, but is in no way + limited, nor controlled by the D-Bus protocol specification. The D-Bus + protocol is one possible application layer on top of kdbus. + </para> + + <para> + For the general D-Bus protocol specification, its payload format, its + marshaling, and its communication semantics, please refer to the + <ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html"> + D-Bus specification</ulink>. + </para> + + </refsect1> + + <refsect1> + <title>Terminology</title> + + <refsect2> + <title>Domain</title> + <para> + A domain is a <emphasis>kdbusfs</emphasis> mount-point containing all + the bus primitives. Each domain is independent, and separate domains + do not affect each other. + </para> + </refsect2> + + <refsect2> + <title>Bus</title> + <para> + A bus is a named object inside a domain. Clients exchange messages + over a bus. Multiple buses themselves have no connection to each other; + messages can only be exchanged on the same bus. The default endpoint of + a bus, to which clients establish connections, is the "bus" file + /sys/fs/kdbus/<bus name>/bus. + Common operating system setups create one "system bus" per system, + and one "user bus" for every logged-in user. Applications or services + may create their own private buses. The kernel driver does not + distinguish between different bus types, they are all handled the same + way. See + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </refsect2> + + <refsect2> + <title>Endpoint</title> + <para> + An endpoint provides a file to talk to a bus. Opening an endpoint + creates a new connection to the bus to which the endpoint belongs. All + endpoints have unique names and are accessible as files underneath the + directory of a bus, e.g., /sys/fs/kdbus/<bus>/<endpoint> + Every bus has a default endpoint called "bus". + A bus can optionally offer additional endpoints with custom names + to provide restricted access to the bus. Custom endpoints carry + additional policy which can be used to create sandboxes with + locked-down, limited, filtered access to a bus. See + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </refsect2> + + <refsect2> + <title>Connection</title> + <para> + A connection to a bus is created by opening an endpoint file of a + bus. Every ordinary client connection has a unique identifier on the + bus and can address messages to every other connection on the same + bus by using the peer's connection ID as the destination. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </refsect2> + + <refsect2> + <title>Pool</title> + <para> + Each connection allocates a piece of shmem-backed memory that is + used to receive messages and answers to ioctl commands from the kernel. + It is never used to send anything to the kernel. In order to access that + memory, an application must mmap() it into its address space. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </refsect2> + + <refsect2> + <title>Well-known Name</title> + <para> + A connection can, in addition to its implicit unique connection ID, + request the ownership of a textual well-known name. Well-known names are + noted in reverse-domain notation, such as com.example.service1. A + connection that offers a service on a bus is usually reached by its + well-known name. An analogy of connection ID and well-known name is an + IP address and a DNS name associated with that address. See + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </refsect2> + + <refsect2> + <title>Message</title> + <para> + Connections can exchange messages with other connections by addressing + the peers with their connection ID or well-known name. A message + consists of a message header with information on how to route the + message, and the message payload, which is a logical byte stream of + arbitrary size. Messages can carry additional file descriptors to be + passed from one connection to another, just like passing file + descriptors over UNIX domain sockets. Every connection can specify which + set of metadata the kernel should attach to the message when it is + delivered to the receiving connection. Metadata contains information + like: system time stamps, UID, GID, TID, proc-starttime, well-known + names, process comm, process exe, process argv, cgroup, capabilities, + seclabel, audit session, loginuid and the connection's human-readable + name. See + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </refsect2> + + <refsect2> + <title>Item</title> + <para> + The API of kdbus implements the notion of items, submitted through and + returned by most ioctls, and stored inside data structures in the + connection's pool. See + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </refsect2> + + <refsect2> + <title>Broadcast, signal, filter, match</title> + <para> + Signals are messages that a receiver opts in for by installing a blob of + bytes, called a 'match'. Signal messages must always carry a + counter-part blob, called a 'filter', and signals are only delivered to + peers which have a match that white-lists the message's filter. Senders + of signal messages can use either a single connection ID as receiver, + or the special connection ID + <constant>KDBUS_DST_ID_BROADCAST</constant> to potentially send it to + all connections of a bus, following the logic described above. See + <citerefentry> + <refentrytitle>kdbus.match</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + and + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </refsect2> + + <refsect2> + <title>Policy</title> + <para> + A policy is a set of rules that define which connections can see, talk + to, or register a well-known name on the bus. A policy is attached to + buses and custom endpoints, and modified by policy holder connections or + owners of custom endpoints. See + <citerefentry> + <refentrytitle>kdbus.policy</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </refsect2> + + <refsect2> + <title>Privileged bus users</title> + <para> + A user connecting to the bus is considered privileged if it is either + the creator of the bus, or if it has the CAP_IPC_OWNER capability flag + set. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </refsect2> + </refsect1> + + <refsect1> + <title>Bus Layout</title> + + <para> + A <emphasis>bus</emphasis> provides and defines an environment that peers + can connect to for message interchange. A bus is created via the kdbus + control interface and can be modified by the bus creator. It applies the + policy that control all bus operations. The bus creator itself does not + participate as a peer. To establish a peer + <emphasis>connection</emphasis>, you have to open one of the + <emphasis>endpoints</emphasis> of a bus. Each bus provides a default + endpoint, but further endpoints can be created on-demand. Endpoints are + used to apply additional policies for all connections on this endpoint. + Thus, they provide additional filters to further restrict access of + specific connections to the bus. + </para> + + <para> + Following, you can see an example bus layout: + </para> + + <programlisting><![CDATA[ + Bus Creator + | + | + +-----+ + | Bus | + +-----+ + | + __________________/ \__________________ + / \ + | | + +----------+ +----------+ + | Endpoint | | Endpoint | + +----------+ +----------+ + _________/|\_________ _________/|\_________ + / | \ / | \ + | | | | | | + | | | | | | + Connection Connection Connection Connection Connection Connection + ]]></programlisting> + + </refsect1> + + <refsect1> + <title>Data structures and interconnections</title> + <programlisting><![CDATA[ + +--------------------------------------------------------------------------+ + | Domain (Mount Point) | + | /sys/fs/kdbus/control | + | +----------------------------------------------------------------------+ | + | | Bus (System Bus) | | + | | /sys/fs/kdbus/0-system/ | | + | | +-------------------------------+ +--------------------------------+ | | + | | | Endpoint | | Endpoint | | | + | | | /sys/fs/kdbus/0-system/bus | | /sys/fs/kdbus/0-system/ep.app | | | + | | +-------------------------------+ +--------------------------------+ | | + | | +--------------+ +--------------+ +--------------+ +---------------+ | | + | | | Connection | | Connection | | Connection | | Connection | | | + | | | :1.22 | | :1.25 | | :1.55 | | :1.81 | | | + | | +--------------+ +--------------+ +--------------+ +---------------+ | | + | +----------------------------------------------------------------------+ | + | | + | +----------------------------------------------------------------------+ | + | | Bus (User Bus for UID 2702) | | + | | /sys/fs/kdbus/2702-user/ | | + | | +-------------------------------+ +--------------------------------+ | | + | | | Endpoint | | Endpoint | | | + | | | /sys/fs/kdbus/2702-user/bus | | /sys/fs/kdbus/2702-user/ep.app | | | + | | +-------------------------------+ +--------------------------------+ | | + | | +--------------+ +--------------+ +--------------+ +---------------+ | | + | | | Connection | | Connection | | Connection | | Connection | | | + | | | :1.22 | | :1.25 | | :1.55 | | :1.81 | | | + | | +--------------+ +--------------+ +--------------------------------+ | | + | +----------------------------------------------------------------------+ | + +--------------------------------------------------------------------------+ + ]]></programlisting> + </refsect1> + + <refsect1> + <title>Metadata</title> + + <refsect2> + <title>When metadata is collected</title> + <para> + kdbus records data about the system in certain situations. Such metadata + can refer to the currently active process (creds, PIDs, current user + groups, process names and its executable path, cgroup membership, + capabilities, security label and audit information), connection + information (description string, currently owned names) and time stamps. + </para> + <para> + Metadata is collected at the following times. + </para> + + <itemizedlist> + <listitem><para> + When a bus is created (<constant>KDBUS_CMD_MAKE</constant>), + information about the calling task is collected. This data is returned + by the kernel via the <constant>KDBUS_CMD_BUS_CREATOR_INFO</constant> + call. + </para></listitem> + + <listitem> + <para> + When a connection is created (<constant>KDBUS_CMD_HELLO</constant>), + information about the calling task is collected. Alternatively, a + privileged connection may provide 'faked' information about + credentials, PIDs and security labels which will be stored instead. + This data is returned by the kernel as information on a connection + (<constant>KDBUS_CMD_CONN_INFO</constant>). Only metadata that a + connection allowed to be sent (by setting its bit in + <varname>attach_flags_send</varname>) will be exported in this way. + </para> + </listitem> + + <listitem> + <para> + When a message is sent (<constant>KDBUS_CMD_SEND</constant>), + information about the sending task and the sending connection are + collected. This metadata will be attached to the message when it + arrives in the receiver's pool. If the connection sending the + message installed faked credentials (see + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>), + the message will not be augmented by any information about the + currently sending task. Note that only metadata that was requested + by the receiving connection will be collected and attached to + messages. + </para> + </listitem> + </itemizedlist> + + <para> + Which metadata items are actually delivered depends on the following + sets and masks: + </para> + + <itemizedlist> + <listitem><para> + (a) the system-wide kmod creds mask + (module parameter <varname>attach_flags_mask</varname>) + </para></listitem> + + <listitem><para> + (b) the per-connection send creds mask, set by the connecting client + </para></listitem> + + <listitem><para> + (c) the per-connection receive creds mask, set by the connecting + client + </para></listitem> + + <listitem><para> + (d) the per-bus minimal creds mask, set by the bus creator + </para></listitem> + + <listitem><para> + (e) the per-bus owner creds mask, set by the bus creator + </para></listitem> + + <listitem><para> + (f) the mask specified when querying creds of a bus peer + </para></listitem> + + <listitem><para> + (g) the mask specified when querying creds of a bus owner + </para></listitem> + </itemizedlist> + + <para> + With the following rules: + </para> + + <itemizedlist> + <listitem> + <para> + [1] The creds attached to messages are determined as + <constant>a & b & c</constant>. + </para> + </listitem> + + <listitem> + <para> + [2] When connecting to a bus (<constant>KDBUS_CMD_HELLO</constant>), + and <constant>~b & d != 0</constant>, the call will fail with, + <errorcode>-1</errorcode>, and <varname>errno</varname> is set to + <constant>ECONNREFUSED</constant>. + </para> + </listitem> + + <listitem> + <para> + [3] When querying creds of a bus peer, the creds returned are + <constant>a & b & f</constant>. + </para> + </listitem> + + <listitem> + <para> + [4] When querying creds of a bus owner, the creds returned are + <constant>a & e & g</constant>. + </para> + </listitem> + </itemizedlist> + + <para> + Hence, programs might not always get all requested metadata items that + it requested. Code must be written so that it can cope with this fact. + </para> + </refsect2> + + <refsect2> + <title>Benefits and heads-up</title> + <para> + Attaching metadata to messages has two major benefits. + + <itemizedlist> + <listitem> + <para> + Metadata attached to messages is gathered at the moment when the + other side calls <constant>KDBUS_CMD_SEND</constant>, or, + respectively, then the kernel notification is generated. There is + no need for the receiving peer to retrieve information about the + task in a second step. This closes a race gap that would otherwise + be inherent. + </para> + </listitem> + <listitem> + <para> + As metadata is delivered along with messages in the same data + blob, no extra calls to kernel functions etc. are needed to gather + them. + </para> + </listitem> + </itemizedlist> + + Note, however, that collecting metadata does come at a price for + performance, so developers should carefully assess which metadata to + really opt-in for. For best practice, data that is not needed as part + of a message should not be requested by the connection in the first + place (see <varname>attach_flags_recv</varname> in + <constant>KDBUS_CMD_HELLO</constant>). + </para> + </refsect2> + + <refsect2> + <title>Attach flags for metadata items</title> + <para> + To let the kernel know which metadata information to attach as items + to the aforementioned commands, it uses a bitmask. In those, the + following <emphasis>attach flags</emphasis> are currently supported. + Both the the <varname>attach_flags_recv</varname> and + <varname>attach_flags_send</varname> fields of + <type>struct kdbus_cmd_hello</type>, as well as the payload of the + <constant>KDBUS_ITEM_ATTACH_FLAGS_SEND</constant> and + <constant>KDBUS_ITEM_ATTACH_FLAGS_RECV</constant> items follow this + scheme. + </para> + + <variablelist> + <varlistentry> + <term><constant>KDBUS_ATTACH_TIMESTAMP</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_TIMESTAMP</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_CREDS</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_CREDS</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_PIDS</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_PIDS</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_AUXGROUPS</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_AUXGROUPS</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_NAMES</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_OWNED_NAME</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_TID_COMM</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_TID_COMM</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_PID_COMM</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_PID_COMM</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_EXE</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_EXE</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_CMDLINE</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_CMDLINE</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_CGROUP</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_CGROUP</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_CAPS</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_CAPS</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_SECLABEL</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_SECLABEL</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_AUDIT</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_AUDIT</constant>. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>KDBUS_ATTACH_CONN_DESCRIPTION</constant></term> + <listitem><para> + Requests the attachment of an item of type + <constant>KDBUS_ITEM_CONN_DESCRIPTION</constant>. + </para></listitem> + </varlistentry> + </variablelist> + + <para> + Please refer to + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for detailed information about the layout and payload of items and + what metadata should be used to. + </para> + </refsect2> + </refsect1> + + <refsect1> + <title>The ioctl interface</title> + + <para> + As stated in the 'synopsis' section above, application developers are + strongly encouraged to use kdbus through one of the high-level D-Bus + abstraction libraries, rather than using the low-level API directly. + </para> + + <para> + kdbus on the kernel level exposes its functions exclusively through + <citerefentry> + <refentrytitle>ioctl</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry>, + employed on file descriptors returned by + <citerefentry> + <refentrytitle>open</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + on pseudo files exposed by + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para> + <para> + Following is a list of all the ioctls, along with the command structs + they must be used with. + </para> + + <informaltable frame="none"> + <tgroup cols="3" colsep="1"> + <thead> + <row> + <entry>ioctl signature</entry> + <entry>command</entry> + <entry>transported struct</entry> + </row> + </thead> + <tbody> + <row> + <entry><constant>0x40189500</constant></entry> + <entry><constant>KDBUS_CMD_BUS_MAKE</constant></entry> + <entry><type>struct kdbus_cmd *</type></entry> + </row><row> + <entry><constant>0x40189510</constant></entry> + <entry><constant>KDBUS_CMD_ENDPOINT_MAKE</constant></entry> + <entry><type>struct kdbus_cmd *</type></entry> + </row><row> + <entry><constant>0xc0609580</constant></entry> + <entry><constant>KDBUS_CMD_HELLO</constant></entry> + <entry><type>struct kdbus_cmd_hello *</type></entry> + </row><row> + <entry><constant>0x40189582</constant></entry> + <entry><constant>KDBUS_CMD_BYEBYE</constant></entry> + <entry><type>struct kdbus_cmd *</type></entry> + </row><row> + <entry><constant>0x40389590</constant></entry> + <entry><constant>KDBUS_CMD_SEND</constant></entry> + <entry><type>struct kdbus_cmd_send *</type></entry> + </row><row> + <entry><constant>0x80409591</constant></entry> + <entry><constant>KDBUS_CMD_RECV</constant></entry> + <entry><type>struct kdbus_cmd_recv *</type></entry> + </row><row> + <entry><constant>0x40209583</constant></entry> + <entry><constant>KDBUS_CMD_FREE</constant></entry> + <entry><type>struct kdbus_cmd_free *</type></entry> + </row><row> + <entry><constant>0x401895a0</constant></entry> + <entry><constant>KDBUS_CMD_NAME_ACQUIRE</constant></entry> + <entry><type>struct kdbus_cmd *</type></entry> + </row><row> + <entry><constant>0x401895a1</constant></entry> + <entry><constant>KDBUS_CMD_NAME_RELEASE</constant></entry> + <entry><type>struct kdbus_cmd *</type></entry> + </row><row> + <entry><constant>0x80289586</constant></entry> + <entry><constant>KDBUS_CMD_LIST</constant></entry> + <entry><type>struct kdbus_cmd_list *</type></entry> + </row><row> + <entry><constant>0x80309584</constant></entry> + <entry><constant>KDBUS_CMD_CONN_INFO</constant></entry> + <entry><type>struct kdbus_cmd_info *</type></entry> + </row><row> + <entry><constant>0x40209551</constant></entry> + <entry><constant>KDBUS_CMD_UPDATE</constant></entry> + <entry><type>struct kdbus_cmd *</type></entry> + </row><row> + <entry><constant>0x80309585</constant></entry> + <entry><constant>KDBUS_CMD_BUS_CREATOR_INFO</constant></entry> + <entry><type>struct kdbus_cmd_info *</type></entry> + </row><row> + <entry><constant>0x40189511</constant></entry> + <entry><constant>KDBUS_CMD_ENDPOINT_UPDATE</constant></entry> + <entry><type>struct kdbus_cmd *</type></entry> + </row><row> + <entry><constant>0x402095b0</constant></entry> + <entry><constant>KDBUS_CMD_MATCH_ADD</constant></entry> + <entry><type>struct kdbus_cmd_match *</type></entry> + </row><row> + <entry><constant>0x402095b1</constant></entry> + <entry><constant>KDBUS_CMD_MATCH_REMOVE</constant></entry> + <entry><type>struct kdbus_cmd_match *</type></entry> + </row> + </tbody> + </tgroup> + </informaltable> + + <para> + Depending on the type of <emphasis>kdbusfs</emphasis> node that was + opened and what ioctls have been executed on a file descriptor before, + a different sub-set of ioctl commands is allowed. + </para> + + <itemizedlist> + <listitem> + <para> + On a file descriptor resulting from opening a + <emphasis>control node</emphasis>, only the + <constant>KDBUS_CMD_BUS_MAKE</constant> ioctl may be executed. + </para> + </listitem> + <listitem> + <para> + On a file descriptor resulting from opening a + <emphasis>bus endpoint node</emphasis>, only the + <constant>KDBUS_CMD_ENDPOINT_MAKE</constant> and + <constant>KDBUS_CMD_HELLO</constant> ioctls may be executed. + </para> + </listitem> + <listitem> + <para> + A file descriptor that was used to create a bus + (via <constant>KDBUS_CMD_BUS_MAKE</constant>) is called a + <emphasis>bus owner</emphasis> file descriptor. The bus will be + active as long as the file descriptor is kept open. + A bus owner file descriptor can not be used to + employ any further ioctls. As soon as + <citerefentry> + <refentrytitle>close</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + is called on it, the bus will be shut down, along will all associated + endpoints and connections. See + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </listitem> + <listitem> + <para> + A file descriptor that was used to create an endpoint + (via <constant>KDBUS_CMD_ENDPOINT_MAKE</constant>) is called an + <emphasis>endpoint owner</emphasis> file descriptor. The endpoint + will be active as long as the file descriptor is kept open. + An endpoint owner file descriptor can only be used + to update details of an endpoint through the + <constant>KDBUS_CMD_ENDPOINT_UPDATE</constant> ioctl. As soon as + <citerefentry> + <refentrytitle>close</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + is called on it, the endpoint will be removed from the bus, and all + connections that are connected to the bus through it are shut down. + See + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + for more details. + </para> + </listitem> + <listitem> + <para> + A file descriptor that was used to create a connection + (via <constant>KDBUS_CMD_HELLO</constant>) is called a + <emphasis>connection owner</emphasis> file descriptor. The connection + will be active as long as the file descriptor is kept open. + A connection owner file descriptor may be used to + issue any of the following ioctls. + </para> + + <itemizedlist> + <listitem><para> + <constant>KDBUS_CMD_UPDATE</constant> to tweak details of the + connection. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + + <listitem><para> + <constant>KDBUS_CMD_BYEBYE</constant> to shut down a connection + without losing messages. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + + <listitem><para> + <constant>KDBUS_CMD_FREE</constant> to free a slice of memory in + the pool. See + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + + <listitem><para> + <constant>KDBUS_CMD_CONN_INFO</constant> to retrieve information + on other connections on the bus. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + + <listitem><para> + <constant>KDBUS_CMD_BUS_CREATOR_INFO</constant> to retrieve + information on the bus creator. See + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + + <listitem><para> + <constant>KDBUS_CMD_LIST</constant> to retrieve a list of + currently active well-known names and unique IDs on the bus. See + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + + <listitem><para> + <constant>KDBUS_CMD_SEND</constant> and + <constant>KDBUS_CMD_RECV</constant> to send or receive a message. + See + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + + <listitem><para> + <constant>KDBUS_CMD_NAME_ACQUIRE</constant> and + <constant>KDBUS_CMD_NAME_RELEASE</constant> to acquire or release + a well-known name on the bus. See + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + + <listitem><para> + <constant>KDBUS_CMD_MATCH_ADD</constant> and + <constant>KDBUS_CMD_MATCH_REMOVE</constant> to add or remove + a match for signal messages. See + <citerefentry> + <refentrytitle>kdbus.match</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry>. + </para></listitem> + </itemizedlist> + </listitem> + </itemizedlist> + + <para> + These ioctls, along with the structs they transport, are explained in + detail in the other documents linked to in the 'see also' section below. + </para> + </refsect1> + + <refsect1> + <title>See Also</title> + <simplelist type="inline"> + <member> + <citerefentry> + <refentrytitle>kdbus.bus</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.connection</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.endpoint</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.fs</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.item</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.message</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.name</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>kdbus.pool</refentrytitle> + <manvolnum>7</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>ioctl</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>mmap</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>open</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + <member> + <citerefentry> + <refentrytitle>close</refentrytitle> + <manvolnum>2</manvolnum> + </citerefentry> + </member> + <member> + <ulink url="http://freedesktop.org/wiki/Software/dbus">D-Bus</ulink> + </member> + </simplelist> + </refsect1> + +</refentry> diff --git a/Documentation/kdbus/stylesheet.xsl b/Documentation/kdbus/stylesheet.xsl new file mode 100644 index 00000000000..52565eac7d0 --- /dev/null +++ b/Documentation/kdbus/stylesheet.xsl @@ -0,0 +1,16 @@ +<?xml version="1.0" encoding="UTF-8"?> +<stylesheet xmlns="http://www.w3.org/1999/XSL/Transform" version="1.0"> + <param name="chunk.quietly">1</param> + <param name="funcsynopsis.style">ansi</param> + <param name="funcsynopsis.tabular.threshold">80</param> + <param name="callout.graphics">0</param> + <param name="paper.type">A4</param> + <param name="generate.section.toc.level">2</param> + <param name="use.id.as.filename">1</param> + <param name="citerefentry.link">1</param> + <strip-space elements="*"/> + <template name="generate.citerefentry.link"> + <value-of select="refentrytitle"/> + <text>.html</text> + </template> +</stylesheet> @@ -1186,6 +1186,7 @@ $(help-board-dirs): help-%: %docs: scripts_basic FORCE $(Q)$(MAKE) $(build)=scripts build_docproc $(Q)$(MAKE) $(build)=Documentation/DocBook $@ + $(Q)$(MAKE) $(build)=Documentation/kdbus $@ else # KBUILD_EXTMOD |