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[Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts |
Date: |
Mon, 13 Sep 2010 16:13:46 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.12) Gecko/20100907 Fedora/3.0.7-1.fc12 Thunderbird/3.0.7 |
Am 13.09.2010 15:42, schrieb Anthony Liguori:
> On 09/13/2010 08:39 AM, Kevin Wolf wrote:
>>> Yeah, one of the key design points of live migration is to minimize the
>>> number of failure scenarios where you lose a VM. If someone typed the
>>> wrong command line or shared storage hasn't been mounted yet and we
>>> delay failure until live migration is in the critical path, that would
>>> be terribly unfortunate.
>>>
>> We would catch most of them if we try to open the image when migration
>> starts and immediately close it again until migration is (almost)
>> completed, so that no other code can possibly use it before the source
>> has really closed it.
>>
>
> I think the only real advantage is that we fix NFS migration, right?
That's the one that we know about, yes.
The rest is not a specific scenario, but a strong feeling that having an
image opened twice at the same time feels dangerous. As soon as an
open/close sequence writes to the image for some format, we probably
have a bug. For example, what about this mounted flag that you were
discussing for QED?
> But if we do invalidate_cache() as you suggested with a close/open of
> the qcow2 layer, and also acquire and release a lock in the file layer
> by propagating the invalidate_cache(), that should work robustly with NFS.
>
> I think that's a simpler change. Do you see additional advantages to
> delaying the open?
Just that it makes it very obvious if a device model is doing bad things
and accessing the image before it should. The difference is a failed
request vs. silently corrupted data.
Kevin
[Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Kevin Wolf, 2010/09/13
- [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Anthony Liguori, 2010/09/13
- [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Kevin Wolf, 2010/09/13
- [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Anthony Liguori, 2010/09/13
- [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts,
Kevin Wolf <=
- Re: [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Anthony Liguori, 2010/09/13
- Re: [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Avi Kivity, 2010/09/14
- Re: [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Anthony Liguori, 2010/09/14
- Re: [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Avi Kivity, 2010/09/14
Re: [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Stefan Hajnoczi, 2010/09/13
Re: [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Kevin Wolf, 2010/09/13
Re: [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Anthony Liguori, 2010/09/13
Re: [Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Kevin Wolf, 2010/09/14
[Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts, Juan Quintela, 2010/09/15
[Qemu-devel] [PATCH 1/3] block: allow migration to work with image files, Anthony Liguori, 2010/09/11