linux-ext4 - Re: Is it deliberate that the device mapper is not passing the DISCARD ioctls

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Date:	Tue, 21 Sep 2010 15:47:16 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	"Theodore Ts'o" <tytso@....edu>, linux-ext4@...r.kernel.org,
	dm-devel@...hat.com
Subject: Re: Is it deliberate that the device mapper is not passing the
 DISCARD ioctls

On Tue, Sep 21, 2010 at 6:42 AM, Lukas Czerner <lczerner@...hat.com> wrote:
> On Mon, 20 Sep 2010, Theodore Ts'o wrote:
>
>> Hi there,
>>
>> I was just testing discard support in mke2fs, and I was surprised that
>> although the dm layer appears to pass discard requests through to the
>> underlying block device driver when submitted through the bio layer
>> (i.e., from kernel file systems), apparently the discard ioctls (i.e.,
>> BLKDISCARD, BLKDISCARDSEC, BLKDISCARDZEROES) are not currently wired up
>> in the dm layer.
>>
>> Is this deliberate, or an oversight?
>>
>> Thanks, regards,
>
> Hi Ted,
>
> I have tested this with 2.6.35 and it really did not work for me as
> well, but with 2.6.36-rc5 (latests kernel) it works just fine. Though,
> not sure when it was added. But according to the log it seems it was
> merged in with 8357422d4bf33bc2c35884d4016c3fc9efbbc1d2.

Makes sense, DM's discard support was added during the 2.6.36 merge window.

Mike
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