[Drbd-dev] [PATCH 03/23] sd: implement REQ_OP_WRITE_ZEROES

[Paolo Bonzini]

On 29/03/2017 18:28, Bart Van Assche wrote:
> On Wed, 2017-03-29 at 16:51 +0200, Paolo Bonzini wrote:
>> On 28/03/2017 20:50, Bart Van Assche wrote:
>>> This means that just like the start and end of a discard must be aligned on a
>>> discard_granularity boundary, WRITE SAME commands with the UNMAP bit set must
>>> also respect that granularity. I think this means that either
>>> __blkdev_issue_zeroout() has to be modified such that it rejects unaligned
>>> REQ_OP_WRITE_ZEROES operations or that blk_bio_write_same_split() has to be
>>> modified such that it generates REQ_OP_WRITEs for the unaligned start and tail.
>>
>> I don't think this is the case.
> 
> Hello Paolo,
> 
> Can you cite the section(s) from the SCSI specs that support your view? I
> reread the "5.49 WRITE SAME (10) command" and "4.7.3.4.4 WRITE SAME command
> and unmap operations" sections but I have not found any explicit statement
> that specifies the behavior for unaligned WRITE SAME commands with the UNMAP
> bit set. It seems to me like the OPTIMAL UNMAP GRANULARITY parameter was
> overlooked when both sections were written. Should we ask the T10 committee
> for a clarification?