linux-ext4 - Re: [dm-devel] do not disable ext4 discards on first discard failure? [was: Re: dm snapshot: ignore discards issued to the snapshot-origin target]

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Message-ID: <20110502081308.GC8642@agk-dp.fab.redhat.com>
Date:	Mon, 2 May 2011 09:13:08 +0100
From:	Alasdair G Kergon <agk@...hat.com>
To:	device-mapper development <dm-devel@...hat.com>
Cc:	Alasdair G Kergon <agk@...hat.com>, sandeen@...hat.com,
	Mike Snitzer <snitzer@...hat.com>,
	Christoph Hellwig <hch@...radead.org>, DarkNovaNick@...il.com,
	linux-lvm@...hat.com, Lukas Czerner <lczerner@...hat.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [dm-devel] do not disable ext4 discards on first discard
	failure? [was: Re: dm snapshot: ignore discards issued to the
	snapshot-origin target]

On Mon, May 02, 2011 at 09:16:21AM +0200, Lukas Czerner wrote:
> However when we have dm device where part of the device supports
> discard due to underlying hardware capability we just can not return
> EOPNOTSUPP from blkdev_issue_discard, because it is just not true! 

EOPNOTSUPP from dm means the operation was not supported on that *one* bio.
It does *not* tell you anything in general about the device, or whether
you'd get the same error from different bios in future.

Alasdair

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