linux-kernel - Re: [ANNOUNCE] Native Linux KVM tool v2

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Date:	Thu, 16 Jun 2011 09:21:03 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Anthony Liguori <anthony@...emonkey.ws>
Cc:	Alexander Graf <agraf@...e.de>,
	Prasad Joshi <prasadjoshi124@...il.com>,
	Avi Kivity <avi@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Sasha Levin <levinsasha928@...il.com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Asias He <asias.hejun@...il.com>,
	Jens Axboe <jaxboe@...ionio.com>
Subject: Re: [ANNOUNCE] Native Linux KVM tool v2

On Thu, Jun 16, 2011 at 1:44 AM, Anthony Liguori <anthony@...emonkey.ws> wrote:
>>> That's probably why it's fast, it doesn't preserve data integrity :(
>>
>> Actually, I misread the code.  It does unstable writes but it does do
>> fsync() on FLUSH.

On Thu, Jun 16, 2011 at 8:41 AM, Pekka Enberg <penberg@...nel.org> wrote:
> Yes. That's fine, right? Or did we misread how virtio block devices
> are supposed to work?

And btw, we use sync_file_range() to make sure the metadata part of a
QCOW2 image is never corrupted. The rational here is that if the guest
doesn't do VIRTIO_BLK_T_FLUSH, you can corrupt your _guest filesystem_
but the _image_ will still work just fine and you can do fsck on it.

Also, Prasad ran xfstests and did over-night stress tests to iron out
corruption issues. Now we obviously can't promise that we'll never eat
your data but I can assure you that we've done as much as we've been
able to with the resources we have at the moment.

                                Pekka
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