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dm crypt: always disable discard_zeroes_data

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If optional discard support in dm-crypt is enabled, discards requests
bypass the crypt queue and blocks of the underlying device are discarded.
For the read path, discarded blocks are handled the same as normal
ciphertext blocks, thus decrypted.

So if the underlying device announces discarded regions return zeroes,
dm-crypt must disable this flag because after decryption there is just
random noise instead of zeroes.

Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Milan Broz 2011-09-25 23:26:21 +01:00 committed by Alasdair G Kergon
parent 8232480944
commit 983c7db347
3 changed files with 26 additions and 0 deletions
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2
drivers/md/dm-crypt.c
View File

@ -1698,6 +1698,8 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
}
ti->num_flush_requests = 1;
ti->discard_zeroes_data_unsupported = 1;
return 0;
bad:

19
drivers/md/dm-table.c
View File

@ -1283,6 +1283,22 @@ static bool dm_table_supports_flush(struct dm_table *t, unsigned flush)
return 0;
}
static bool dm_table_discard_zeroes_data(struct dm_table *t)
{
struct dm_target *ti;
unsigned i = 0;
/* Ensure that all targets supports discard_zeroes_data. */
while (i < dm_table_get_num_targets(t)) {
ti = dm_table_get_target(t, i++);
if (ti->discard_zeroes_data_unsupported)
return 0;
}
return 1;
}
void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
struct queue_limits *limits)
{
@ -1305,6 +1321,9 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
}
blk_queue_flush(q, flush);
if (!dm_table_discard_zeroes_data(t))
q->limits.discard_zeroes_data = 0;
dm_table_set_integrity(t);
/*

5
include/linux/device-mapper.h
View File

@ -197,6 +197,11 @@ struct dm_target {
* whether or not its underlying devices have support.
*/
unsigned discards_supported:1;
/*
* Set if this target does not return zeroes on discarded blocks.
*/
unsigned discard_zeroes_data_unsupported:1;
};
/* Each target can link one of these into the table */