On Mon, Aug 08 2011 at 5:48pm -0400,
Milan Broz <mbroz@xxxxxxxxxx> wrote:
> If optional discard support in dm-crypt is enabled,
> discards requests bypass crypt queue and blocks
> of the underlying device are discarded.
>
> But for read path, discarded blocks are handled
> as the same as normal ciphertext blocks, thus decrypted.
>
> So if 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@xxxxxxxxxx>
> ---
> drivers/md/dm-crypt.c | 1 +
> drivers/md/dm-table.c | 19 +++++++++++++++++++
> include/linux/device-mapper.h | 5 +++++
> 3 files changed, 25 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> index 49da55c..b6ac710 100644
> --- a/drivers/md/dm-crypt.c
> +++ b/drivers/md/dm-crypt.c
> @@ -1698,6 +1698,7 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
> }
>
> ti->num_flush_requests = 1;
> + ti->discard_zeroes_unsupported = 1;
I'd prefer 'discard_zeroes_data_unsupported'
> return 0;
>
> bad:
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 61d3e83..5294f29 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1330,6 +1330,22 @@ static bool dm_table_is_nonrot(struct dm_table *t)
> return 1;
> }
>
> +static bool dm_table_discard_zeroes(struct dm_table *t)
Likewise, dm_table_discard_zeroes_data().
> +{
> + struct dm_target *ti;
> + unsigned i = 0;
> +
> + /* Ensure that all targets supports discard zeroes. */
> + while (i < dm_table_get_num_targets(t)) {
> + ti = dm_table_get_target(t, i++);
> +
> + if (ti->discard_zeroes_unsupported)
> + return 0;
> + }
> +
> + return 1;
> +}
> +
> void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
> struct queue_limits *limits)
> {
> @@ -1357,6 +1373,9 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
> else
> queue_flag_clear_unlocked(QUEUE_FLAG_NONROT, q);
>
> + if (!dm_table_discard_zeroes(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 ba99936..2416cf1 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -208,6 +208,11 @@ 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_unsupported:1;
> };
>
> /* Each target can link one of these into the table */
> --
> 1.7.5.4
>
> --
> dm-devel mailing list
> dm-devel@xxxxxxxxxx
> https://www.redhat.com/mailman/listinfo/dm-devel
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