From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Mon, 2 May 2011 09:13:08 +0100
From: Alasdair G Kergon <agk@redhat.com>
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Subject: Re: [linux-lvm] [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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To: device-mapper development <dm-devel@redhat.com>
Cc: sandeen@redhat.com, Mike Snitzer <snitzer@redhat.com>, Christoph Hellwig <hch@infradead.org>, DarkNovaNick@gmail.com, linux-lvm@redhat.com, Lukas Czerner <lczerner@redhat.com>, linux-ext4@vger.kernel.org, Alasdair G Kergon <agk@redhat.com>

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