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dm thin: do not send discards to shared blocks 

When process_discard receives a partial discard that doesn't cover a
full block, it sends this discard down to that block. Unfortunately, the
block can be shared and the discard would corrupt the other snapshots
sharing this block.

This patch detects block sharing and ends the discard with success when
sending it to the shared block.

The above change means that if the device supports discard it can't be
guaranteed that a discard request zeroes data. Therefore, we set
ti->discard_zeroes_data_unsupported.

Thin target discard support with this bug arrived in commit
104655fd4d (dm thin: support discards).

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mikulas Patocka 2012-07-20 14:25:05 +01:00 committed by Alasdair G Kergon
parent 751f188dd5
commit 650d2a06b4
1 changed files with 5 additions and 1 deletions
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6
drivers/md/dm-thin.c
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@ -1245,7 +1245,10 @@ static void process_discard(struct thin_c *tc, struct bio *bio)
cell_release_singleton(cell, bio);
cell_release_singleton(cell2, bio);
remap_and_issue(tc, bio, lookup_result.block);
if ((!lookup_result.shared) && pool->pf.discard_passdown)
remap_and_issue(tc, bio, lookup_result.block);
else
bio_endio(bio, 0);
}
break;
@ -2628,6 +2631,7 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
if (tc->pool->pf.discard_enabled) {
ti->discards_supported = 1;
ti->num_discard_requests = 1;
ti->discard_zeroes_data_unsupported = 1;
}
dm_put(pool_md);