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>
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@ -300,8 +300,10 @@ static void __insert_origin(struct origin *o)
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* Returns number of snapshots registered using the supplied cow device, plus:
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* snap_src - a snapshot suitable for use as a source of exception handover
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* snap_dest - a snapshot capable of receiving exception handover.
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* snap_merge - an existing snapshot-merge target linked to the same origin.
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* There can be at most one snapshot-merge target. The parameter is optional.
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*
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* Possible return values and states:
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* Possible return values and states of snap_src and snap_dest.
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* 0: NULL, NULL - first new snapshot
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* 1: snap_src, NULL - normal snapshot
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* 2: snap_src, snap_dest - waiting for handover
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@ -310,7 +312,8 @@ static void __insert_origin(struct origin *o)
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*/
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static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
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struct dm_snapshot **snap_src,
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struct dm_snapshot **snap_dest)
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struct dm_snapshot **snap_dest,
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struct dm_snapshot **snap_merge)
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{
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struct dm_snapshot *s;
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struct origin *o;
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@ -322,6 +325,8 @@ static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
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goto out;
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list_for_each_entry(s, &o->snapshots, list) {
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if (dm_target_is_snapshot_merge(s->ti) && snap_merge)
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*snap_merge = s;
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if (!bdev_equal(s->cow->bdev, snap->cow->bdev))
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continue;
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@ -349,9 +354,11 @@ out:
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static int __validate_exception_handover(struct dm_snapshot *snap)
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{
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struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
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struct dm_snapshot *snap_merge = NULL;
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/* Does snapshot need exceptions handed over to it? */
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if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest) == 2) ||
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if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest,
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&snap_merge) == 2) ||
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snap_dest) {
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snap->ti->error = "Snapshot cow pairing for exception "
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"table handover failed";
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@ -365,6 +372,20 @@ static int __validate_exception_handover(struct dm_snapshot *snap)
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if (!snap_src)
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return 0;
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/*
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* Non-snapshot-merge handover?
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*/
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if (!dm_target_is_snapshot_merge(snap->ti))
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return 1;
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/*
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* Do not allow more than one merging snapshot.
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*/
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if (snap_merge) {
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snap->ti->error = "A snapshot is already merging.";
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return -EINVAL;
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}
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return 1;
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}
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@ -933,7 +954,7 @@ static void snapshot_dtr(struct dm_target *ti)
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down_read(&_origins_lock);
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/* Check whether exception handover must be cancelled */
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(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest);
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(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
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if (snap_src && snap_dest && (s == snap_src)) {
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down_write(&snap_dest->lock);
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snap_dest->valid = 0;
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@ -1399,7 +1420,7 @@ static int snapshot_preresume(struct dm_target *ti)
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struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
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down_read(&_origins_lock);
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(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest);
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(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
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if (snap_src && snap_dest) {
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down_read(&snap_src->lock);
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if (s == snap_src) {
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@ -1424,7 +1445,7 @@ static void snapshot_resume(struct dm_target *ti)
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struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
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down_read(&_origins_lock);
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(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest);
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(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
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if (snap_src && snap_dest) {
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down_write(&snap_src->lock);
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down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);
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