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From: | Anthony Liguori |
Subject: | [Qemu-devel] Re: [PATCH] Disable O_DIRECT for physical CDROM/DVD drives |
Date: | Tue, 20 Jul 2010 11:03:40 -0500 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.10) Gecko/20100528 Lightning/1.0b1 Thunderbird/3.0.5 |
On 07/20/2010 11:02 AM, Jes Sorensen wrote:
On 07/20/10 17:40, Anthony Liguori wrote:On 07/20/2010 10:17 AM, 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. Signed-off-by: Jes Sorensen<address@hidden>Wouldn't a better solution be to have a cdrom_read/cdrom_write hook that did the appropriate bouncing? Silently disabling something a user explicitly asked for is not a good option. In the very least, it should error out entirely.I thought about this, but it would require basically fixing up or copying all of the pread/pwrite code to use the right block size. This is really more of a band-aid but it should be pretty safe.
Please throw an error. If a user explicitly asks for something, and we can provide it, we should not continue. Changing it to something else is a bug.
That doesn't apply when we're changing a default value, but if the user asks for something, we should give it to them or fail.
Regards, Anthony Liguori
Cheers, Jes
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