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Re: [Qemu-devel] [PATCH v3] Error on O_DIRECT for physical CDROM/DVD dri
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [PATCH v3] Error on O_DIRECT for physical CDROM/DVD drives |
Date: |
Wed, 21 Jul 2010 16:13:10 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) |
Christoph Hellwig <address@hidden> writes:
> On Wed, Jul 21, 2010 at 09:45:19AM +0200, address@hidden wrote:
>> From: Jes Sorensen <address@hidden>
>>
>> O_DIRECT (cache=none) requires sector alignment, however the physical
>> sector size of CDROM/DVD drives is 2048, as opposed to most disk
>> devices which use 512. QEMU is hard coding 512 all over the place, so
>> allowing O_DIRECT for CDROM/DVD devices does not work.
>>
>> Return -ENOTSUP from cdrom_open() in this case.
>
> The patch is not quite correct. There are CDROMs with 512 byte sectors,
> just as there are disks with larger sector sizes. And of course these
> limitations also apply when running ontop of filesystems.
>
> So we really need to handle these things better and need to query
> the sector size of the device and handle it properly.
Agreed, but I figure Jes's fix is the best we can do for .13, and worth
doing for .13.