[sbuild::chroot_fs_union] New class to add filesysten union support

Introduces a new type of chroot options.  This allows chroot
sessions to be generated using an unioning filesystem like aufs
or unionfs.  Per default this feature is disabled.  Check out
schroot.conf.5 for further information.

1 files changed, 78 insertions, 2 deletions

diff --git a/etc/setup.d/10mount b/etc/setup.d/10mount
index 8b09caab..6052ebf3 100755
--- a/etc/setup.d/10mount
+++ b/etc/setup.d/10mount
@@ -41,10 +41,15 @@ do_mount()
     fi
     if [ ! -d "$3" ]; then
 	echo "$3 does not exist, and could not be created"
-	exit 1
+	return 1
     fi
 
+    set +e
     mount $VERBOSE $1 "$2" "$3"
+    RESULT=$?
+    set -e
+
+    return $RESULT
 }
 
 # Unmount all filesystems under specified location
@@ -65,6 +70,59 @@ do_umount_all()
     fi
 }
 
+# Mount a filesystem union
+# $1: read-only branch
+do_mount_fs_union()
+{
+    MOUNT_RES=255
+
+    # Try mounting the filesystem module
+    if ! grep -q "${CHROOT_FS_UNION_TYPE}$" /proc/filesystems; then
+	set +e
+	modprobe ${CHROOT_FS_UNION_TYPE} &> /dev/null
+	set -e
+    fi
+
+    # Skip fs if not available
+    if ! grep -q "${CHROOT_FS_UNION_TYPE}$" /proc/filesystems; then
+	# branch config just works with the first fs
+	CHROOT_FS_UNION_BRANCH_CONFIG=""
+	continue
+    fi
+
+    # Prepare branch config for fs type
+    if [ "x" = "x${CHROOT_FS_UNION_BRANCH_CONFIG}" ]; then
+	case $CHROOT_FS_UNION_TYPE in
+	unionfs)
+	    CHROOT_FS_UNION_BRANCH_CONFIG="dirs=${CHROOT_FS_UNION_OVERLAY_DIRECTORY}=rw,${1}=ro"
+	    ;;
+	aufs)
+	    CHROOT_FS_UNION_BRANCH_CONFIG="br:${CHROOT_FS_UNION_OVERLAY_DIRECTORY}:${1}=ro"
+	    ;;
+	esac
+    fi
+
+    # Try mounting fs
+    set +e
+    mount -t $CHROOT_FS_UNION_TYPE -o "$CHROOT_FS_UNION_BRANCH_CONFIG" ${CHROOT_NAME} ${CHROOT_MOUNT_LOCATION}
+    MOUNT_RES=$?
+    set -e
+    if [ 0 -eq $MOUNT_RES ]; then
+	break
+    fi
+
+    if [ 0 -ne $MOUNT_RES ]; then
+	echo "Mounting filesystem union failed"
+	return 1
+    fi
+
+    if [ "$AUTH_VERBOSITY" = "verbose" ]; then
+	echo "Using '$CHROOT_FS_UNION_TYPE' for filesystem union"
+    fi
+
+    return 0
+}
+
 if [ "$AUTH_VERBOSITY" = "verbose" ]; then
   VERBOSE="-v"
 #  FSCK_VERBOSE="-V"
@@ -72,6 +130,14 @@ fi
 
 if [ "$CHROOT_TYPE" = "plain" ] || [ "$CHROOT_TYPE" = "directory" ] || [ "$CHROOT_TYPE" = "file" ] || [ "$CHROOT_TYPE" = "file" ] || [ "$CHROOT_TYPE" = "loopback" ] || [ "$CHROOT_TYPE" = "block-device" ] || [ "$CHROOT_TYPE" = "lvm-snapshot" ]; then
 
+    if [ "xnone" != "x${CHROOT_FS_UNION_TYPE:-none}" ] \
+	&& [ "$CHROOT_SESSION_PURGE" = "true" ];
+    then
+	CREATE_FS_UNION="yes"
+    else
+	CREATE_FS_UNION="no"
+    fi
+
     if [ "$CHROOT_TYPE" = "plain" ]; then
 	CHROOT_MOUNT_OPTIONS="--rbind"
 	CHROOT_MOUNT_DEVICE="$CHROOT_DIRECTORY"
@@ -105,7 +171,17 @@ if [ "$CHROOT_TYPE" = "plain" ] || [ "$CHROOT_TYPE" = "directory" ] || [ "$CHROO
 	    do_umount_all "$CHROOT_MOUNT_LOCATION"
 	fi
 
-	do_mount "$CHROOT_MOUNT_OPTIONS" "$CHROOT_MOUNT_DEVICE" "$CHROOT_MOUNT_LOCATION"
+	if [ "xyes" = "x${CREATE_FS_UNION}" ]; then
+	    if ! do_mount_fs_union "$CHROOT_FS_UNION_RO_BRANCH"
+	    then
+		exit 1
+	    fi
+	else
+	    if ! do_mount "$CHROOT_MOUNT_OPTIONS" "$CHROOT_MOUNT_DEVICE" "$CHROOT_MOUNT_LOCATION"
+	    then
+		exit 1
+	    fi
+	fi
 
 	if [ "$CHROOT_TYPE" != "plain" ]; then
 	    if [ -n "$FSTAB" ]; then