There are no dm_get_queue_limits() callers outside of DM core and
there shouldn't be.

Also, remove its BUG_ON(!atomic_read(&md->holders)) to micro-optimize
__process_abnormal_io().

Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Introduce max_write_zeroes_granularity and
max_secure_erase_granularity flags in the dm_target struct.

If a target sets these then DM core will split IO of these operation
types accordingly (in terms of max_write_zeroes_sectors and
max_secure_erase_sectors respectively).

Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Eliminate duplicate boilerplate code for simple modules that contain
a single DM target driver without any additional setup code.

Add a new module_dm() macro, which replaces the module_init() and
module_exit() with template functions that call dm_register_target()
and dm_unregister_target() respectively.

Signed-off-by: Yangtao Li <frank.li@vivo.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

The block core (bio_split_discard) will already split discards based
on the 'discard_granularity' and 'max_discard_sectors' queue_limits.
But the DM thin target also needs to ensure that it doesn't receive a
discard that spans a 'max_discard_sectors' boundary.

Introduce a dm_target 'max_discard_granularity' flag that if set will
cause DM core to split discard bios relative to 'max_discard_sectors'.
This treats 'discard_granularity' as a "min_discard_granularity" and
'max_discard_sectors' as a "max_discard_granularity".

Requested-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

'GPL-2.0-only' is used instead of 'GPL-2.0' because SPDX has
deprecated its use.

Suggested-by: John Wiele <jwiele@redhat.com>
Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Commit ca522482e3eaf ("dm: pass NULL bdev to bio_alloc_clone")
introduced the optimization to _not_ perform bio_associate_blkg()'s
relatively costly work when DM core clones its bio. But in doing so it
exposed the possibility for DM's cloned bio to alter DM target
behavior (e.g. crash) if a target were to issue IO without first
calling bio_set_dev().

The DM raid target can trigger an MD crash due to its need to split
the DM bio that is passed to md_handle_request(). The split will
recurse to submit_bio_noacct() using a bio with an uninitialized
->bi_blkg. This NULL bio->bi_blkg causes blk_throtl_bio() to
dereference a NULL blkg_to_tg(bio->bi_blkg).

Fix this in DM core by adding a new 'needs_bio_set_dev' target flag that
will make alloc_tio() call bio_set_dev() on behalf of the target.
dm-raid is the only target that requires this flag. bio_set_dev()
initializes the DM cloned bio's ->bi_blkg, using bio_associate_blkg,
before passing the bio to md_handle_request().

Long-term fix would be to audit and refactor MD code to rely on DM to
split its bio, using dm_accept_partial_bio(), but there are MD raid
personalities (e.g. raid1 and raid10) whose implementation are tightly
coupled to handling the bio splitting inline.

Fixes: ca522482e3eaf ("dm: pass NULL bdev to bio_alloc_clone")
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

More efficient and readable to just access table->num_targets directly.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>