From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [PATCH 03/23] sd: implement REQ_OP_WRITE_ZEROES Date: Wed, 29 Mar 2017 16:28:01 +0000 Message-ID: <1490804856.3551.3.camel@sandisk.com> References: <20170323143341.31549-1-hch@lst.de> <20170323143341.31549-4-hch@lst.de> <1490726988.2573.16.camel@sandisk.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: Content-Language: en-US Content-ID: <7F521760D57C1746ACD169C42D3C2D16@sandisk.com> Sender: linux-scsi-owner@vger.kernel.org To: "agk@redhat.com" , "lars.ellenberg@linbit.com" , "snitzer@redhat.com" , "hch@lst.de" , "martin.petersen@oracle.com" , "philipp.reisner@linbit.com" , "axboe@kernel.dk" , "pbonzini@redhat.com" , "shli@kernel.org" Cc: "linux-scsi@vger.kernel.org" , "dm-devel@redhat.com" , "drbd-dev@lists.linbit.com" , "linux-block@vger.kernel.org" , "linux-raid@vger.kernel.org" List-Id: linux-raid.ids 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 aligne= d on a > > discard_granularity boundary, WRITE SAME commands with the UNMAP bit se= t must > > also respect that granularity. I think this means that either > > __blkdev_issue_zeroout() has to be modified such that it rejects unalig= ned > > REQ_OP_WRITE_ZEROES operations or that blk_bio_write_same_split() has t= o be > > modified such that it generates REQ_OP_WRITEs for the unaligned start a= nd tail. >=20 > 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 UNMA= P bit set. It seems to me like=A0the OPTIMAL UNMAP GRANULARITY parameter was overlooked when both sections were written. Should we ask the T10 committee for a clarification? Another question is, if the specification of WRITE SAME + UNMAP would be made unambiguous in the SBC document, whether or not we should take the ris= k to trigger behavior that is not what we expect by sending unaligned WRITE SAME + UNMAP commands to SCSI devices? Thanks, Bart.=