Mount snaphsots on <mnt>/@/<id>/m

Instead of mounting snapshot overlays on <mnt>/@/<id>
mount them on <mnt>/@/<id>/m so as not to hide the upper
dir at <mnt>/@/<id>/u.

More changes to mount.snapshot:
- With no snapshots in stack mount pass through
  snapshot mount without creating a snapshot
- Check for overlapping snapshot mounts

scripts/mount.snapshot

@@ -3,10 +3,10 @@
 #
 # Overlayfs snapshot mount helper
 #
-# - Create snapshot dir <mnt>/@ and snapshot 0 if non exists
+# - Check if snapshots stack exists at <mnt>/@/.snapshots
 # - Bind shared mount at <mnt>/@
 # - Mount snapshot mount at <mnt>
-# - Mount olds snapshots at <mnt>/@/<id>..
+# - Mount olds snapshots at <mnt>/@/<id>/m
 #
 # * If any mount flags other than -o rw are passed to helper,
 #   it passes the command as is without doing the above
@@ -47,108 +47,95 @@ error()
 # No support for mount options at the moment
 if [ -n "$*" -a "$*" != "-o rw" ]; then
 	echo "$*" > /tmp/mount.snapshot.in
-	mount -i -t snapshot "$dev" "$mnt" $*
-	exit $?
+	exec mount -i -t snapshot "$dev" "$mnt" $*
 fi
 
 # Verify that overlayfs snapshot feature is enabled
 grep -wq 'overlay' /proc/filesystems || modprobe overlay
 grep -wq 'snapshot' /proc/filesystems || \
 	error "overlayfs snapshots feature not enabled."
 
-# Verify snapshot is not already mounted - nesting is not allowed
-! grep -q "^\S\+ $mnt snapshot" /proc/mounts || \
-	error "overlayfs snapshot already mounted at $mnt."
+# Verify snapshot is not already mounted on child or parent path
+# because nesting is not allowed
+mounted=$(mount -t snapshot | while read d on m opt; do echo $m; done)
+for m in $mounted; do
+	if ( echo $m | grep -q "^$mnt" ) || ( echo $mnt | grep -q "^$m" ); then
+		error "overlapping overlayfs snapshot already mounted at '$m'."
+	fi
+done
 
 lower="$mnt"
 snapdir="$mnt/@"
 snapshots="$snapdir/.snapshots"
 
-# If we create snapdir, we should remove it on failure
-[ -d "$snapdir" ] || cleanup_snapdir=true
-
-id=0
 [ ! -s "$snapshots" ] || id=$(tail -n 1 "$snapshots")
 
+if [ -z "$id" ]; then
+	# No current snapshot - mount pass through snapshot mount
+	exec mount -i -t snapshot "$dev" "$mnt" -o"upperdir=$lower"
+fi
+
 cd "$lower" || exit 1
 
 # Relative to $lower to keep overlay mount options shorter
-base="@/$id"
-upper="$base/u"
-work="$base/w"
-snap="$base"
-
-# If we create a new snapshot, we should remove it on failure
-[ -d "$snap" ] || new_snap=true
+current="@/$id"
+upper="$current/u"
+work="$current/w"
+snapmnt="$current/m"
 
 tmpdir=/tmp/snapshot.$$
-tmpsnap="$tmpdir/$id"
+tmpmnt="$tmpdir/$id/m"
 trap "_cleanup" 0 1 2 3 15
 _cleanup()
 {
 	err=$?
 	# Cleanup snapshot $id temp mounts
-	umount -i "$tmpsnap" 2>/dev/null
+	umount -i "$tmpmnt" 2>/dev/null
 	umount -i "$tmpdir" 2>/dev/null
 	umount -i "$snapdir" 2>/dev/null
 	rmdir $tmpdir 2>/dev/null
-	if [ $err != 0 ]; then
-		# Cleanup new created directories on failure
-		[ -z "$new_snap" ] || rm -rf "$mnt/$snap"
-		[ -z "$cleanup_snapdir" ] || rm -rf "$snapdir"
-	fi
 	exit $err
 }
 
 mount_old_snapshots()
 {
-	local old_snapshots=$snap
+	local old_snapshots=$snapmnt
 
 	# mount snapshots from newest to oldest
 	tac "$snapshots" | while read old; do
 		[ "$old" != "$id" ] || continue
 		oldsnap="@/$old"
-		delsnap="@/.$old"
-		oldmnt=
-		if [ -d "$oldsnap" ]; then
-			# mount only non-deleted snapshots
-			oldmnt="$oldsnap"
-		elif [ -d "$delsnap" ]; then
-			# but chain deleted snapshot in lower
-			oldsnap="$delsnap"
-		else
-			continue
-		fi
+		oldmnt="$oldsnap/m"
+		[ -d "$oldsnap" ] || continue
 		old_snapshots="$oldsnap/u:$old_snapshots"
-		[ -n "$oldmnt" ] || continue
+		[ -d "$oldmnt" ] || continue
 		mount -i -t overlay "$dev@$old" "$oldmnt" \
 			-o"ro,lowerdir=$old_snapshots"
 	done
 }
 
-# Create new snapshot dir with empty upper/work
-mkdir -p "$snap" "$upper" "$work" || exit 1
+# Verify current snapshot dirs
+[ -d "$snapmnt" -a -d "$upper" -a -d "$work" ] || \
+	error "missing snapshot '$current' directories."
 
-# Whiteout snapshots dir inside upper
-[ -c "$upper/@" ] || mknod "$upper/@" c 0 0 || exit 1
+# Verify whiteout of snapshots dir inside upper
+[ -c "$upper/@" ] || \
+	error "missing whiteout of snapshot '$current' directories."
 
 # Make shared mount clone of the real lower mount
-mount --bind "$snapdir" "$snapdir"
-mount --make-shared "$snapdir"
-mkdir -p "$tmpdir"
-mount --bind "$snapdir" "$tmpdir"
+mount --bind "$snapdir" "$snapdir" || exit 1
+mount --make-shared "$snapdir" || exit 1
+mkdir -p "$tmpdir" || exit 1
+mount --bind "$snapdir" "$tmpdir" || exit 1
 
-# Mount the snapshot overlay and snapshot mount
+# Mount the current snapshot overlay and snapshot mount
 mount -i -t overlay "$dev@$id" -o"lowerdir=$lower,upperdir=$upper,workdir=$work" \
-	"$snap" || exit 1
-mount -i -t snapshot "$dev@$id" -o"upperdir=$lower,snapshot=$snap" \
+	"$snapmnt" || exit 1
+mount -i -t snapshot "$dev@$id" -o"upperdir=$lower,snapshot=$snapmnt" \
 	"$mnt" || exit 1
 
-# Write new snapshot id to snapshots stack
-grep -qs "^$id$" "$snapshots" || echo "$id" >> "$snapshots"
-
-# Bind the (now covered) snapshot overlay above the snapshot mount
-mount --bind -r "$tmpsnap" "$mnt/$snap" || exit 1
+# Bind the (now covered) current snapshot overlay above the snapshot mount
+mount --bind -r "$tmpmnt" "$mnt/$snapmnt" || exit 1
 
 # Mount older snapshots
 mount_old_snapshots

scripts/ovlsnapshot

@@ -72,7 +72,7 @@ parse_path_snapshot_arg()
 	# directory inside <path> to store snapshot related files
 	SNAPDIR=$MNT/@
 	# directory prefix for snapshot mount points
-	# snaphot mount points will be created as $SNAPMNT<snapshot-name>
+	# snaphot mount points will be created as $SNAPMNT<snapshot-name>/m
 	SNAPMNT=$MNT/@/
 	# file to store snapshots stack
 	SNAPSHOTS="$SNAPDIR/.snapshots"
@@ -118,7 +118,7 @@ snapshot_in_stack()
 
 snapshot_is_deleted()
 {
-	[ ! -d $SNAPDIR/$1 ]
+	[ ! -d $SNAPDIR/$1/m ]
 }
 
 snapshot_exists()
@@ -130,7 +130,7 @@ snapshot_exists()
 		[ -s $SNAPSHOTS ]
 	else
 		# Does snapshot $s exist?
-		[ -d $SNAPDIR/$s ] || [ -d $SNAPDIR/.$s ] || snapshot_in_stack $s
+		[ -d $SNAPDIR/$s ] || snapshot_in_stack $s
 	fi
 }
 
@@ -140,6 +140,7 @@ create_snapshot()
 
 	mkdir -p $SNAPDIR/$s/u || exit 1
 	mkdir -p $SNAPDIR/$s/w || exit 1
+	mkdir -p $SNAPDIR/$s/m || exit 1
 	mknod $SNAPDIR/$s/u/@ c 0 0 || exit 1
 	echo $s >> $SNAPSHOTS || exit 1
 	sync
@@ -149,18 +150,18 @@ delete_snapshot()
 {
 	local s=$1
 
-	umount -i $SNAPDIR/$s 2>/dev/null
+	umount -i $SNAPDIR/$s/m 2>/dev/null
 	rm -rf $SNAPDIR/$s/w || exit 1
-	mv $SNAPDIR/$s $SNAPDIR/.$s|| exit 1
+	rm -rf $SNAPDIR/$s/m || exit 1
 	sync
 }
 
 remove_snapshot()
 {
 	local s=$1
 
-	snapshot_is_deleted $s || delete_snapshot $s
-	rm -rf $SNAPDIR/.$s || exit 1
+	umount -i $SNAPDIR/$s/m 2>/dev/null
+	rm -rf $SNAPDIR/$s || exit 1
 	grep -v "^$1$" $SNAPSHOTS > $SNAPSHOTS.tmp
 	sync
 	mv $SNAPSHOTS.tmp $SNAPSHOTS
@@ -174,7 +175,7 @@ snapshot_is_mounted()
 	if [ -z "$s" ]; then
 		grep -q "^\S\+ $MNT snapshot" /proc/mounts
 	else
-		grep -q "^\S\+ $SNAPMNT$s overlay" /proc/mounts
+		grep -q "^\S\+ $SNAPMNT$s/m overlay" /proc/mounts
 	fi
 }
 
@@ -434,7 +435,7 @@ case "$CMD" in
 		d=$TESTDIR
 	else
 		echo "Files in snapshot $snap:"
-		d=$SNAPMNT$snap/$SNAPTEST
+		d=$SNAPMNT$snap/m/$SNAPTEST
 	fi
 	if [ -d $d ] ; then
 		cd $d > /dev/null
@@ -455,15 +456,15 @@ case "$CMD" in
 	[ -z "$3" ] || N=$3
 	$0 umount $MNT
 	for s in $( cat $SNAPSHOTS 2> /dev/null ) ; do
-		$0 remove $SNAPMNT$s 2> /dev/null
+		$0 remove $SNAPDIR/$s 2> /dev/null
 	done
 	$0 mount $MNT
 	for n in $( seq 0 $N ) ; do
 		$0 test $MNT $n $4 || exit 1
 	done
 	$0 lstest $MNT
 	for n in $( seq 1 $N ) ; do
-		$0 lstest $SNAPMNT$n
+		$0 lstest $SNAPDIR/$n
 	done
 	;;
   test)
@@ -509,7 +510,7 @@ case "$CMD" in
 	cd - > /dev/null
 	$0 lstest $MNT || exit 1
 	s=$n
-	$0 take $SNAPMNT$s || exit 1
+	$0 take $SNAPDIR/$s || exit 1
 	case "$n" in
   	  1)
 		echo Create test:
@@ -541,12 +542,12 @@ case "$CMD" in
 		f=1
 		echo 'Restoring from snapshot' $f
 		rm -rf $TESTDIR/?
-		cp -R $SNAPMNT$f/$SNAPTEST/? $TESTDIR/
+		cp -R $SNAPMNT$f/m/$SNAPTEST/? $TESTDIR/
 	  ;;
 	esac || exit 1
 	echo .
 	$0 lstest $MNT || exit 1
-	$0 lstest $SNAPMNT$s || exit 1
+	$0 lstest $SNAPDIR/$s || exit 1
 	$0 list $MNT
 	;;
 

scripts/umount.snapshot

@@ -3,8 +3,9 @@
 #
 # Overlayfs snapshot umount helper
 #
-# - Unmount snapshot overlays listed in <mnt>/@/snapshots
+# - Unmount snapshot overlays <mnt>/@/*/m
 # - Unmount snapshot mount at <mnt>
+# - Unmount shared mount at <mnt>/@
 #
 #-----------------------------------------------------------------------
 #
@@ -47,12 +48,12 @@ umount_snapshots()
 {
 	# Unmount snapshot overlays recorded in snapshots stack
 	[ ! -s "$snapshots" ] || cat "$snapshots" | while read id; do
-		umount -i "$snapdir/$id" 2>/dev/null
+		umount -i "$snapdir/$id/m" 2>/dev/null
 	done
 
 	# Cleanup leftover snapshot overlays not recorded in snapshots stack
 	if grep -q "^\S\+@\S\+ $snapdir/\S\+ overlay" /proc/mounts; then
-		umount -i "$snapdir"/* 2>/dev/null
+		umount -i "$snapdir"/*/m 2>/dev/null
 	fi
 }