Re: 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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Subject: Re: do not disable ext4 discards on first discard failure? [was: Re: dm snapshot: ignore discards issued to the snapshot-origin target]
From: Alasdair G Kergon <agk@xxxxxxxxxx>
Date: Mon, 2 May 2011 09:13:08 +0100
Cc: sandeen@xxxxxxxxxx, Mike Snitzer <snitzer@xxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, DarkNovaNick@xxxxxxxxx, linux-lvm@xxxxxxxxxx, Lukas Czerner <lczerner@xxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, Alasdair G Kergon <agk@xxxxxxxxxx>
In-reply-to: <alpine.LFD.2.00.1105020857030.3778@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Mail-followup-to: device-mapper development <dm-devel@xxxxxxxxxx>, Alasdair G Kergon <agk@xxxxxxxxxx>, sandeen@xxxxxxxxxx, Mike Snitzer <snitzer@xxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, DarkNovaNick@xxxxxxxxx, linux-lvm@xxxxxxxxxx, Lukas Czerner <lczerner@xxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx
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References: <20cf301cbef67d323104a0c2ff52@xxxxxxxxxx> <20110413224025.GA18589@xxxxxxxxxx> <20110413234854.GA19793@xxxxxxxxxx> <20110426173213.GA19604@xxxxxxxxxx> <20110428001912.GA14659@xxxxxxxxxx> <20110428075355.GA2190@xxxxxxxxxxxxx> <20110428205935.GA24979@xxxxxxxxxx> <alpine.LFD.2.00.1104291117510.5496@xxxxxxxxxxxxxxxxxxxxxxxxxx> <20110429122454.GL32370@xxxxxxxxxxxxxxxxxxxxx> <alpine.LFD.2.00.1105020857030.3778@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Reply-to: device-mapper development <dm-devel@xxxxxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)

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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Follow-Ups:
- Re: do not disable ext4 discards on first discard failure? [was: Re: dm snapshot: ignore discards issued to the snapshot-origin target]
  - From: Christoph Hellwig

References:
- [PATCH] dm snapshot: add discard support to the snapshot-origin target [was: Re: Testing TRIM with LVM]
  - From: Mike Snitzer
- Re: dm snapshot: add discard support to the snapshot-origin target [was: Re: Testing TRIM with LVM]
  - From: Mike Snitzer
- Re: dm snapshot: add discard support to the snapshot-origin target [was: Re: Testing TRIM with LVM]
  - From: Mike Snitzer
- [PATCH] dm snapshot: ignore discards issued to the snapshot-origin target
  - From: Mike Snitzer
- Re: [PATCH] dm snapshot: ignore discards issued to the snapshot-origin target
  - From: Christoph Hellwig
- do not disable ext4 discards on first discard failure? [was: Re: dm snapshot: ignore discards issued to the snapshot-origin target]
  - From: Mike Snitzer
- Re: do not disable ext4 discards on first discard failure? [was: Re: dm snapshot: ignore discards issued to the snapshot-origin target]
  - From: Lukas Czerner
- Re: do not disable ext4 discards on first discard failure? [was: Re: dm snapshot: ignore discards issued to the snapshot-origin target]
  - From: Alasdair G Kergon
- Re: do not disable ext4 discards on first discard failure? [was: Re: dm snapshot: ignore discards issued to the snapshot-origin target]
  - From: Lukas Czerner

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