Commit 93c1defedcae ("rbd: remove the discard_zeroes_data flag")
explicitly didn't implement REQ_OP_WRITE_ZEROES for rbd, while the
following commit 48920ff2a5a9 ("block: remove the discard_zeroes_data
flag") dropped ->discard_zeroes_data in favor of REQ_OP_WRITE_ZEROES.
rbd does support efficient zeroing via CEPH_OSD_OP_ZERO opcode and will
release either some or all blocks depending on whether the zeroing
request is rbd_obj_bytes() aligned. This is how we currently implement
discards, so REQ_OP_WRITE_ZEROES can be identical to REQ_OP_DISCARD for
now. Caveats:
- REQ_NOUNMAP is ignored, but AFAICT that's true of at least two other
current implementations - nvme and loop
- there is no ->write_zeroes_alignment and blk_bio_write_zeroes_split()
is hence less helpful than blk_bio_discard_split(), but this can (and
should) be fixed on the rbd side
In the future we will split these into two code paths to respect
REQ_NOUNMAP on zeroout and save on zeroing blocks that couldn't be
released on discard.
Fixes: 93c1defedcae ("rbd: remove the discard_zeroes_data flag")
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jason Dillaman <dillaman@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
6ac56951dc