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Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image |
Date: |
Thu, 21 Mar 2013 09:08:39 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
On 03/21/2013 08:56 AM, Stefan Hajnoczi wrote:
> On Thu, Mar 21, 2013 at 02:42:23PM +0100, Paolo Bonzini wrote:
>> Il 21/03/2013 14:38, Stefan Hajnoczi ha scritto:
>>> There already is a guest RAM cloning mechanism: fork the QEMU process.
>>> Then you have a copy-on-write guest RAM.
>>>
>>> In a little more detail:
>>>
>>> 1. save non-RAM device state
>>> 2. quiesce QEMU to a state that is safe for forking
>>> 3. create an EventNotifier for live savevm completion signal
>>> 4. fork and pass completion EventNotifier to child
>>> 5. parent continues running VM
>>> 6. child performs vmsave of copy-on-write guest RAM
>>> 7. child signals completion EventNotifier and terminates
>>> 8. parent raises live savevm completion QMP event
>>
>> Forking a threaded program is not so easy, but it could be done if the
>> child is very simple and only uses syscalls to communicate back with the
>> parent:
>
> On Linux you should be able to use clone(2) to spawn a thread with
> copy-on-write memory. Too bad it's not portable because it gets around
> the messy fork issues.
And introduces its own messy issues - once you clone() using different
flags than what fork() does, you have invalidated the use of a LOT of
libc interfaces in that child; in particular, any use of pthread is
liable to break.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, (continued)
- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, Pavel Hrdina, 2013/03/18
- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, Wenchao Xia, 2013/03/21
- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, Pavel Hrdina, 2013/03/21
- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, Stefan Hajnoczi, 2013/03/21
- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, Paolo Bonzini, 2013/03/21
- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, Pavel Hrdina, 2013/03/21
- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, Stefan Hajnoczi, 2013/03/21
- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image,
Eric Blake <=
- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, Wenchao Xia, 2013/03/23
- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, Wenchao Xia, 2013/03/26
- Re: [Qemu-devel] [RFC] qmp interface for save vmstate to image, Pavel Hrdina, 2013/03/21