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Commit 9d3b15c4 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
Browse files

dm snapshot: permit only one merge at once 



Merging more than one snapshot is not supported, so prevent
this happening.

Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 10b8106a

drivers/md/dm-snap.c

+27 −6
Original line number Diff line number Diff line
@@ -300,8 +300,10 @@ static void __insert_origin(struct origin *o) 
 * 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 void __insert_origin(struct origin *o) 
 */

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 @@ static int __find_snapshots_sharing_cow(struct dm_snapshot *snap, 
		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 __find_snapshots_sharing_cow(struct dm_snapshot *snap, 
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 @@ static int __validate_exception_handover(struct dm_snapshot *snap) 
	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 @@ static void snapshot_dtr(struct dm_target *ti) 


	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 @@ static int snapshot_preresume(struct dm_target *ti) 
	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 @@ static void snapshot_resume(struct dm_target *ti) 
	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);