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    SubjectRe: [PATCH RFC 2/8] dm: Add support for block provisioning
    On Thu, Sep 15 2022 at 12:48P -0400,
    Sarthak Kukreti <sarthakkukreti@chromium.org> wrote:

    > From: Sarthak Kukreti <sarthakkukreti@chromium.org>
    >
    > Add support to dm devices for REQ_OP_PROVISION. The default mode
    > is to pass through the request and dm-thin will utilize it to provision
    > blocks.
    >
    > Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
    > ---
    > drivers/md/dm-crypt.c | 4 +-
    > drivers/md/dm-linear.c | 1 +
    > drivers/md/dm-table.c | 17 +++++++
    > drivers/md/dm-thin.c | 86 +++++++++++++++++++++++++++++++++--
    > drivers/md/dm.c | 4 ++
    > include/linux/device-mapper.h | 6 +++
    > 6 files changed, 113 insertions(+), 5 deletions(-)
    >
    > diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
    > index 159c6806c19b..357f0899cfb6 100644
    > --- a/drivers/md/dm-crypt.c
    > +++ b/drivers/md/dm-crypt.c
    > @@ -3081,6 +3081,8 @@ static int crypt_ctr_optional(struct dm_target *ti, unsigned int argc, char **ar
    > if (ret)
    > return ret;
    >
    > + ti->num_provision_bios = 1;
    > +
    > while (opt_params--) {
    > opt_string = dm_shift_arg(&as);
    > if (!opt_string) {
    > @@ -3384,7 +3386,7 @@ static int crypt_map(struct dm_target *ti, struct bio *bio)
    > * - for REQ_OP_DISCARD caller must use flush if IO ordering matters
    > */
    > if (unlikely(bio->bi_opf & REQ_PREFLUSH ||
    > - bio_op(bio) == REQ_OP_DISCARD)) {
    > + bio_op(bio) == REQ_OP_DISCARD || bio_op(bio) == REQ_OP_PROVISION)) {
    > bio_set_dev(bio, cc->dev->bdev);
    > if (bio_sectors(bio))
    > bio->bi_iter.bi_sector = cc->start +
    > diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
    > index 3212ef6aa81b..1aa782149428 100644
    > --- a/drivers/md/dm-linear.c
    > +++ b/drivers/md/dm-linear.c
    > @@ -61,6 +61,7 @@ static int linear_ctr(struct dm_target *ti, unsigned int argc, char **argv)
    > ti->num_discard_bios = 1;
    > ti->num_secure_erase_bios = 1;
    > ti->num_write_zeroes_bios = 1;
    > + ti->num_provision_bios = 1;
    > ti->private = lc;
    > return 0;
    >
    > diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
    > index 332f96b58252..b7f9cb66b7ba 100644
    > --- a/drivers/md/dm-table.c
    > +++ b/drivers/md/dm-table.c
    > @@ -1853,6 +1853,18 @@ static bool dm_table_supports_write_zeroes(struct dm_table *t)
    > return true;
    > }
    >
    > +static bool dm_table_supports_provision(struct dm_table *t)
    > +{
    > + for (unsigned int i = 0; i < t->num_targets; i++) {
    > + struct dm_target *ti = dm_table_get_target(t, i);
    > +
    > + if (ti->num_provision_bios)
    > + return true;
    > + }
    > +
    > + return false;
    > +}
    > +

    This needs to go a step further and verify a device in the stack
    actually services REQ_OP_PROVISION.

    Please see dm_table_supports_discards(): it iterates all devices in
    the table and checks that support is advertised.

    For discard, DM requires that _all_ devices in a table advertise
    support (that is pretty strict and likely could be relaxed to _any_).

    You'll need ti->provision_supported (like ->discards_supported) to
    advertise actual support is provided by dm-thinp (even if underlying
    devices don't support it).

    And yeah, dm-thinp passdown support for REQ_OP_PROVISION can follow
    later as needed (if there actual HW that would benefit from
    REQ_OP_PROVISION).

    Mike

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