From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <1494478235.16894.115.camel@haakon3.risingtidesystems.com> Subject: Re: [PATCH 25/27] block: remove the discard_zeroes_data flag From: "Nicholas A. Bellinger" To: "hch@lst.de" Cc: Bart Van Assche , "agk@redhat.com" , "lars.ellenberg@linbit.com" , "snitzer@redhat.com" , "martin.petersen@oracle.com" , "philipp.reisner@linbit.com" , "axboe@kernel.dk" , "shli@kernel.org" , "linux-scsi@vger.kernel.org" , "dm-devel@redhat.com" , "drbd-dev@lists.linbit.com" , "linux-block@vger.kernel.org" , "target-devel@vger.kernel.org" , "linux-raid@vger.kernel.org" Date: Wed, 10 May 2017 21:50:35 -0700 In-Reply-To: <20170510140627.GA23759@lst.de> References: <20170405172125.22600-1-hch@lst.de> <20170405172125.22600-26-hch@lst.de> <1493671519.2665.15.camel@sandisk.com> <1493707425.23202.77.camel@haakon3.risingtidesystems.com> <1493709373.23202.79.camel@haakon3.risingtidesystems.com> <20170502072328.GA11522@lst.de> <1493782395.23202.84.camel@haakon3.risingtidesystems.com> <20170507092209.GA27370@lst.de> <1494312374.16894.36.camel@haakon3.risingtidesystems.com> <20170510140627.GA23759@lst.de> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-ID: On Wed, 2017-05-10 at 16:06 +0200, hch@lst.de wrote: > On Mon, May 08, 2017 at 11:46:14PM -0700, Nicholas A. Bellinger wrote: > > That said, simply propagating up q->limits.max_write_zeroes_sectors as > > dev_attrib->unmap_zeroes_data following existing code still looks like > > the right thing to do. > > It is not. Martin has decoupled write same/zeroes support from discard > support. Any device will claim to support it initially, and we'll > only clear the flag if a Write Same command fails. > > So even if LBPRZ is not set you can trivially get into a situation > where discard is supported through UNMAP, and you'll incorrectly > set LBPRZ and will cause data corruption. In that case, there are two choices. 1) Expose a block_device or request_queue bit to signal 'real LBPRZ' support up to IBLOCK, in order to maintain SCSI target feature compatibility. 2) Or drop the LBPRZ bit usage for IBLOCK all-together. Since I happen happen to support a block driver that has 'real LBPRZ' support for all discards, I'd prefer the latter so this doesn't have to be carried out-of-tree. So what are the options for this in post v4.12..?