From: Anthony Liguori <anthony@codemonkey.ws>
To: Christoph Hellwig <hch@lst.de>
Cc: Kevin Wolf <kwolf@redhat.com>,
qemu-devel@nongnu.org, Avi Kivity <avi@redhat.com>
Subject: Re: [Qemu-devel] [PATCH] block: Flush image after open
Date: Wed, 09 Mar 2011 11:38:35 -0600 [thread overview]
Message-ID: <4D77BB1B.9030704@codemonkey.ws> (raw)
In-Reply-To: <20110309172757.GA2884@lst.de>
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
>
next prev parent reply other threads:[~2011-03-09 17:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-09 16:15 [Qemu-devel] [PATCH] block: Flush image after open Kevin Wolf
2011-03-09 17:27 ` Christoph Hellwig
2011-03-09 17:38 ` Anthony Liguori [this message]
2011-03-21 12:23 ` Avi Kivity
2011-03-21 13:02 ` Kevin Wolf
2011-03-21 13:21 ` Avi Kivity
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