[PATCH v4 12/13] dm snapshot: redirect accesses to origin if merging snap invalidated

Mike Snitzer
2009-11-20T20:28:29Z

If we are merging an invalidated snapshot, redirect all accesses to the
origin device. This is safe because snapshot_merge_process() will
stop_merge() if the merging snapshot becomes invalid.

Allowing the origin device to remain functional is important because it
may contain the root filesystem.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
---
drivers/md/dm-snap.c | 9 ++++-----
1 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 2b5b083..74f7f38 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1554,11 +1554,9 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,

down_write(&s->lock);

- /* Full snapshots are not usable */
- if (!s->valid) {
- r = -EIO;
- goto out_unlock;
- }
+ /* Full merging snapshots are redirected to the origin */
+ if (!s->valid)
+ goto redirect_to_origin;

/* If the block is already remapped - use that */
e = dm_lookup_exception(&s->complete, chunk);
@@ -1581,6 +1579,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
goto out_unlock;
}

+ redirect_to_origin:
bio->bi_bdev = s->origin->bdev;

if (bio_rw(bio) == WRITE) {
--
1.6.5.2