Re: [Qemu-devel] [PATCH] block: Flush image after open

[Anthony Liguori <anthony@codemonkey.ws>]

On 03/09/2011 11:27 AM, Christoph Hellwig wrote:
> On Wed, Mar 09, 2011 at 05:15:53PM +0100, Kevin Wolf wrote:
>> Quoting the bug report:
>>
>>      qemu ensures that guest writes and qemu metadata writes hit the disk
>>      when necessary to prevent data corruption. However, if an image was
>>      in host pagecache prior to starting qemu, for example after running
>>      qemu-img convert, then nothing prevents writes from reaching the
>>      disk out of order, potentially causing corruption.
>>
>> I'm not entirely sure if there is a realistic case where we would get
>> corruption, but it's probably a case of better safe than sorry.
> Except for SCSI with ordered tags (which we don't support) there are not
> ordering guarantees in the storage protocols, and as such the above explanation
> doesn't make any sense at all.

Even if there was, a guest shouldn't be relying on the ordering of a 
write that comes from a non-guest.

I don't understand the failure scenario here.

Regards,

Anthony Liguori

>