dm crypt: always disable discard_zeroes_data

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>

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 49da55c1528aa01137a61c98d6033c9b84dc2e05..8c2a000cf3f5c2f887f7097cb866d0c3e41f2d7d 100644 (file)
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -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:

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 3226698070774ee511cd697eafd782548eddcadf..bc04518e9d8b588edc5682442c05e425eb15c451 100644 (file)
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -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);
 
        /*

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 3fa1f3d90ce0e21cb3ba27fa98d3201252f91f8e..99e3e50b5c571a3cb9448b69891b95796f1f6ddf 100644 (file)
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -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 */