virtfs root filesystem support

Qemu/KVM provides virtfs, a paravirtualised filesystem that is
implemented by running the Plan 9 folder sharing protocol over
virtio.

Make booting with root=virtfs:foobar use the virtfs filesystem
with mount tag 'foobar' as root filesystem, to allow booting
virtual machines off virtfs.

Note that this only handles 9p over virtio (i.e. virtfs), and
doesn't attempt to handle mounting 9p filesystems over TCP/IP,
for example.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>

4 files changed, 112 insertions, 0 deletions

diff --git a/dracut.spec b/dracut.spec
index 074cb10a..9cd08b7b 100644
--- a/dracut.spec
+++ b/dracut.spec
@@ -270,6 +270,7 @@ rm -rf $RPM_BUILD_ROOT
 %{dracutlibdir}/modules.d/95zfcp
 %{dracutlibdir}/modules.d/95terminfo
 %{dracutlibdir}/modules.d/95udev-rules
+%{dracutlibdir}/modules.d/95virtfs
 %{dracutlibdir}/modules.d/96securityfs
 %{dracutlibdir}/modules.d/97biosdevname
 %{dracutlibdir}/modules.d/97masterkey
diff --git a/modules.d/95virtfs/module-setup.sh b/modules.d/95virtfs/module-setup.sh
new file mode 100755
index 00000000..a6081c21
--- /dev/null
+++ b/modules.d/95virtfs/module-setup.sh
@@ -0,0 +1,27 @@
+#!/bin/bash
+# -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
+# ex: ts=8 sw=4 sts=4 et filetype=sh
+
+check() {
+    [[ $hostonly ]] || [[ $mount_needs ]] && {
+        for fs in ${host_fs_types[@]}; do
+            strstr "$fs" "\|9p" && return 0
+        done
+        return 1
+    }
+
+    return 0
+}
+
+depends() {
+    return 0
+}
+
+installkernel() {
+    instmods 9p 9pnet_virtio
+}
+
+install() {
+    inst_hook cmdline 95 "$moddir/parse-virtfs.sh"
+    inst_hook mount 99 "$moddir/mount-virtfs.sh"
+}
diff --git a/modules.d/95virtfs/mount-virtfs.sh b/modules.d/95virtfs/mount-virtfs.sh
new file mode 100755
index 00000000..dfebf38e
--- /dev/null
+++ b/modules.d/95virtfs/mount-virtfs.sh
@@ -0,0 +1,75 @@
+#!/bin/sh
+# -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
+# ex: ts=8 sw=4 sts=4 et filetype=sh
+
+type getarg >/dev/null 2>&1 || . /lib/dracut-lib.sh
+
+filter_rootopts() {
+    rootopts=$1
+    # strip ro and rw options
+    local OLDIFS="$IFS"
+    IFS=,
+    set -- $rootopts
+    IFS="$OLDIFS"
+    local v
+    while [ $# -gt 0 ]; do
+        case $1 in
+            rw|ro);;
+            defaults);;
+            *)
+                v="$v,${1}";;
+        esac
+        shift
+    done
+    rootopts=${v#,}
+    echo $rootopts
+}
+
+mount_root() {
+    local _ret
+
+    rootfs="9p"
+    rflags="trans=virtio,version=9p2000.L"
+
+    modprobe 9pnet_virtio
+
+    mount -t ${rootfs} -o "$rflags",ro "${root#virtfs:}" "$NEWROOT"
+
+    rootopts=
+    if getargbool 1 rd.fstab -n rd_NO_FSTAB \
+        && ! getarg rootflags \
+        && [ -f "$NEWROOT/etc/fstab" ] \
+        && ! [ -L "$NEWROOT/etc/fstab" ]; then
+        # if $NEWROOT/etc/fstab contains special mount options for
+        # the root filesystem,
+        # remount it with the proper options
+        rootopts="defaults"
+        while read dev mp fs opts rest; do
+            # skip comments
+            [ "${dev%%#*}" != "$dev" ] && continue
+
+            if [ "$mp" = "/" ]; then
+                rootopts=$opts
+                break
+            fi
+        done < "$NEWROOT/etc/fstab"
+
+        rootopts=$(filter_rootopts $rootopts)
+    fi
+
+    # we want rootflags (rflags) to take precedence so prepend rootopts to
+    # them; rflags is guaranteed to not be empty
+    rflags="${rootopts:+"${rootopts},"}${rflags}"
+
+    umount "$NEWROOT"
+
+    info "Remounting ${root#virtfs:} with -o ${rflags}"
+    mount -t ${rootfs} -o "$rflags" "${root#virtfs:}" "$NEWROOT" 2>&1 | vinfo
+
+    [ -f "$NEWROOT"/forcefsck ] && rm -f "$NEWROOT"/forcefsck 2>/dev/null
+    [ -f "$NEWROOT"/.autofsck ] && rm -f "$NEWROOT"/.autofsck 2>/dev/null
+}
+
+if [ -n "$root" -a -z "${root%%virtfs:*}" ]; then
+    mount_root
+fi
diff --git a/modules.d/95virtfs/parse-virtfs.sh b/modules.d/95virtfs/parse-virtfs.sh
new file mode 100755
index 00000000..ce6de6d4
--- /dev/null
+++ b/modules.d/95virtfs/parse-virtfs.sh
@@ -0,0 +1,9 @@
+#!/bin/sh
+# -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
+# ex: ts=8 sw=4 sts=4 et filetype=sh
+
+if [ "${root%%:*}" = "virtfs" ] ; then
+    modprobe 9pnet_virtio
+
+    rootok=1
+fi