Messages in this thread | | | Date | Thu, 5 Nov 2015 09:06:42 +0100 | From | Jan Kara <> | Subject | Re: [PATCH] brd: Refuse improperly aligned discard requests |
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On Thu 05-11-15 04:18:49, Elliott, Robert (Persistent Memory) wrote: > > > -----Original Message----- > > From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel- > > owner@vger.kernel.org] On Behalf Of Jan Kara > > Sent: Wednesday, November 4, 2015 10:14 AM > > To: axboe@kernel.dk > > Cc: LKML <linux-kernel@vger.kernel.org>; linux-fsdevel@vger.kernel.org; > > Christoph Hellwig <hch@infradead.org>; Jan Kara <jack@suse.com> > > Subject: [PATCH] brd: Refuse improperly aligned discard requests > > > > Currently when improperly aligned discard request is submitted, we just > > silently discard more / less data which results in filesystem corruption > > in some cases. Refuse such misaligned requests. > > I agree discarding more than requested is very bad. > > If they are routed to SCSI or ATA devices, though, the discard commands > (SCSI UNMAP or ATA DATA SET MANAGEMENT/TRIM) are just hints, so there > is no guarantee the discard will do anything. Are you finding > filesystems that still don't understand that? dm-raid held that > mistaken assumption for a long time.
So there is blkdev_issue_zeroout() which uses blkdev_issue_discard() if 'discard_zeroes_data' is set. I'd hope that in that case zeroing really happens as submitted or error is returned... Filesystems definitely depend on blkdev_issue_zeroout() doing what it is told.
Honza -- Jan Kara <jack@suse.com> SUSE Labs, CR
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