fstab-generator: add x-systemd.requires and x-systemd.requires-mounts-for

Currently we have no way how to specify dependencies between fstab
entries (or another units) in the /etc/fstab. It means that users are
forced to bypass fstab and write .mount units manually.

The patch introduces new systemd fstab options:

x-systemd.requires=<PATH>

 - to specify dependence an another mount (PATH is translated to unit name)

x-systemd.requires=<UNIT>

 - to specify dependence on arbitrary UNIT

x-systemd.requires-mounts-for=<PATH ...>

 - to specify dependence on another paths, implemented by
   RequiresMountsFor=. The option may be specified more than once.

For example two bind mounts where B depends on A:

 /mnt/test/A    /mnt/test/A     none    bind,defaults
 /mnt/test/A    /mnt/test/B     none    bind,x-systemd.requires=/mnt/test/A

More complex example with overlay FS where one mount point depends on
"low" and "upper" directories:

 /dev/sdc1   /mnt/low    ext4     defaults
 /dev/sdc2   /mnt/high   ext4     defaults
 overlay     /mnt/merged overlay  lowerdir=/mnt/low,upperdir=/mnt/high/data,workdir=/mnt/high/work,x-systemd.requires-mounts-for=/mnt/low,x-systemd.requires-mounts-for=mnt/high

https://bugzilla.redhat.com/show_bug.cgi?id=812826
https://bugzilla.redhat.com/show_bug.cgi?id=1164334

1 files changed, 30 insertions, 0 deletions

diff --git a/man/systemd.mount.xml b/man/systemd.mount.xml
index 862f42e594..ffffc56936 100644
--- a/man/systemd.mount.xml
+++ b/man/systemd.mount.xml
@@ -139,6 +139,36 @@
     <variablelist class='fstab-options'>
 
       <varlistentry>
+        <term><option>x-systemd.requires=</option></term>
+
+        <listitem><para>Configures a <varname>Requires=</varname> and
+        an <varname>After=</varname> dependency between the created
+        mount unit and another systemd unit, such as a device or mount
+        unit. The argument should be a unit name, or an absolute path
+        to a device node or mount point.  This option may be specified
+        more than once. This option is particularly useful for mount
+        point declarations that need an additional device to be around
+        (such as an external journal device for journal file systems)
+        or an additional mount to be in place (such as an overlay file
+        system that merges multiple mount points). See
+        <varname>After=</varname> and <varname>Requires=</varname> in
+        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        for details.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><option>x-systemd.requires-mounts-for=</option></term>
+
+        <listitem><para>Configures a
+        <varname>RequiresMountsFor=</varname> dependency between the
+        created mount unit and other mount units. The argument must be
+        an absolute path. This option may be specified more than once.
+        See <varname>RequiresMountsFor=</varname> in
+        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        for details.</para></listitem>
+       </varlistentry>
+
+      <varlistentry>
         <term><option>x-systemd.automount</option></term>
 
         <listitem><para>An automount unit will be created for the file