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authorMikulas Patocka <mpatocka@redhat.com>2009-12-10 23:52:31 +0000
committerAlasdair G Kergon <agk@redhat.com>2009-12-10 23:52:31 +0000
commit3452c2a1eb5b93c1b9fb0d22bd5b07c0cee4dc29 (patch)
tree65d4af8d6cf36ac4bcc8c226f8be891740d343ee /drivers/md/dm-snap.c
parent515ad66cc4c82f210d726340349c8f7c1ec6b125 (diff)
downloadlinaro-lsk-3452c2a1eb5b93c1b9fb0d22bd5b07c0cee4dc29.tar.gz
dm snapshot: avoid allocating exceptions in merge
The snapshot-merge target should not allocate new exceptions because the intent is to merge all of its exceptions as quickly and safely as possible. This patch introduces the snapshot-merge mapping function and updates __origin_write() so that it doesn't allocate exceptions on any snapshots that are being merged. If a write request to a merging snapshot device is to be dispatched directly to the origin (because the chunk is not remapped or was already merged), snapshot_merge_map() must make exceptions in other snapshots so calls do_origin(). 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>
Diffstat (limited to 'drivers/md/dm-snap.c')
-rw-r--r--drivers/md/dm-snap.c57
1 files changed, 56 insertions, 1 deletions
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index c01e0dafec3..59d9ef6f505 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1308,6 +1308,54 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
return r;
}
+/*
+ * A snapshot-merge target behaves like a combination of a snapshot
+ * target and a snapshot-origin target. It only generates new
+ * exceptions in other snapshots and not in the one that is being
+ * merged.
+ *
+ * For each chunk, if there is an existing exception, it is used to
+ * redirect I/O to the cow device. Otherwise I/O is sent to the origin,
+ * which in turn might generate exceptions in other snapshots.
+ */
+static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
+ union map_info *map_context)
+{
+ struct dm_exception *e;
+ struct dm_snapshot *s = ti->private;
+ int r = DM_MAPIO_REMAPPED;
+ chunk_t chunk;
+
+ chunk = sector_to_chunk(s->store, bio->bi_sector);
+
+ down_read(&s->lock);
+
+ /* Full snapshots are not usable */
+ if (!s->valid) {
+ r = -EIO;
+ goto out_unlock;
+ }
+
+ /* If the block is already remapped - use that */
+ e = dm_lookup_exception(&s->complete, chunk);
+ if (e) {
+ remap_exception(s, e, bio, chunk);
+ goto out_unlock;
+ }
+
+ bio->bi_bdev = s->origin->bdev;
+
+ if (bio_rw(bio) == WRITE) {
+ up_read(&s->lock);
+ return do_origin(s->origin, bio);
+ }
+
+out_unlock:
+ up_read(&s->lock);
+
+ return r;
+}
+
static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
int error, union map_info *map_context)
{
@@ -1465,6 +1513,13 @@ static int __origin_write(struct list_head *snapshots, sector_t sector,
/* Do all the snapshots on this origin */
list_for_each_entry (snap, snapshots, list) {
+ /*
+ * Don't make new exceptions in a merging snapshot
+ * because it has effectively been deleted
+ */
+ if (dm_target_is_snapshot_merge(snap->ti))
+ continue;
+
down_write(&snap->lock);
/* Only deal with valid and active snapshots */
@@ -1697,7 +1752,7 @@ static struct target_type merge_target = {
.module = THIS_MODULE,
.ctr = snapshot_ctr,
.dtr = snapshot_dtr,
- .map = snapshot_map,
+ .map = snapshot_merge_map,
.end_io = snapshot_end_io,
.postsuspend = snapshot_postsuspend,
.preresume = snapshot_preresume,