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Date: Tue, 20 Jul 2010 18:09:45 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] Re: [PATCH] Disable O_DIRECT for physical CDROM/DVD
	drives
References: <1279639056-20465-1-git-send-email-Jes.Sorensen@redhat.com>
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Jes.Sorensen@redhat.com, qemu-devel@nongnu.org

Am 20.07.2010 17:40, schrieb Anthony Liguori:
> On 07/20/2010 10:17 AM, Jes.Sorensen@redhat.com wrote:
>> From: Jes Sorensen<Jes.Sorensen@redhat.com>
>>
>> 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.
>>
>> Signed-off-by: Jes Sorensen<Jes.Sorensen@redhat.com>
>>    
> 
> Wouldn't a better solution be to have a cdrom_read/cdrom_write hook that 
> did the appropriate bouncing?

We already have code that does some bouncing, we'd just need to teach it
to use different sizes than 512. Duplicating everything wouldn't be a
nice solution.

> Silently disabling something a user explicitly asked for is not a good 
> option.  In the very least, it should error out entirely.

Yeah, that's probably better.

Kevin