Commit 650d2a06 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
Browse files

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

Thin target discard support with this bug arrived in commit

 (dm thin: support discards).
Signed-off-by: default avatarMikulas Patocka <>
Signed-off-by: default avatarMike Snitzer <>
Signed-off-by: default avatarAlasdair G Kergon <>
parent 751f188d
......@@ -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);
bio_endio(bio, 0);
......@@ -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;
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