dm snapshot: permit only one merge at once
Merging more than one snapshot is not supported, so prevent
this happening.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 23e3396..7ddee7c 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -300,8 +300,10 @@
* Returns number of snapshots registered using the supplied cow device, plus:
* snap_src - a snapshot suitable for use as a source of exception handover
* snap_dest - a snapshot capable of receiving exception handover.
+ * snap_merge - an existing snapshot-merge target linked to the same origin.
+ * There can be at most one snapshot-merge target. The parameter is optional.
*
- * Possible return values and states:
+ * Possible return values and states of snap_src and snap_dest.
* 0: NULL, NULL - first new snapshot
* 1: snap_src, NULL - normal snapshot
* 2: snap_src, snap_dest - waiting for handover
@@ -310,7 +312,8 @@
*/
static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
struct dm_snapshot **snap_src,
- struct dm_snapshot **snap_dest)
+ struct dm_snapshot **snap_dest,
+ struct dm_snapshot **snap_merge)
{
struct dm_snapshot *s;
struct origin *o;
@@ -322,6 +325,8 @@
goto out;
list_for_each_entry(s, &o->snapshots, list) {
+ if (dm_target_is_snapshot_merge(s->ti) && snap_merge)
+ *snap_merge = s;
if (!bdev_equal(s->cow->bdev, snap->cow->bdev))
continue;
@@ -349,9 +354,11 @@
static int __validate_exception_handover(struct dm_snapshot *snap)
{
struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
+ struct dm_snapshot *snap_merge = NULL;
/* Does snapshot need exceptions handed over to it? */
- if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest) == 2) ||
+ if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest,
+ &snap_merge) == 2) ||
snap_dest) {
snap->ti->error = "Snapshot cow pairing for exception "
"table handover failed";
@@ -365,6 +372,20 @@
if (!snap_src)
return 0;
+ /*
+ * Non-snapshot-merge handover?
+ */
+ if (!dm_target_is_snapshot_merge(snap->ti))
+ return 1;
+
+ /*
+ * Do not allow more than one merging snapshot.
+ */
+ if (snap_merge) {
+ snap->ti->error = "A snapshot is already merging.";
+ return -EINVAL;
+ }
+
return 1;
}
@@ -933,7 +954,7 @@
down_read(&_origins_lock);
/* Check whether exception handover must be cancelled */
- (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest);
+ (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
if (snap_src && snap_dest && (s == snap_src)) {
down_write(&snap_dest->lock);
snap_dest->valid = 0;
@@ -1399,7 +1420,7 @@
struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
down_read(&_origins_lock);
- (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest);
+ (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
if (snap_src && snap_dest) {
down_read(&snap_src->lock);
if (s == snap_src) {
@@ -1424,7 +1445,7 @@
struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
down_read(&_origins_lock);
- (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest);
+ (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
if (snap_src && snap_dest) {
down_write(&snap_src->lock);
down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);