[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image f
From: |
Juan Quintela |
Subject: |
Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2) |
Date: |
Mon, 14 Nov 2011 21:15:48 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux) |
Kevin Wolf <address@hidden> wrote:
> Am 14.11.2011 20:49, schrieb Anthony Liguori:
>> On 11/14/2011 01:46 PM, Juan Quintela wrote:
>>> Anthony Liguori<address@hidden> wrote:
>>>> On 11/14/2011 07:11 AM, Juan Quintela wrote:
>>>>>
>>>>>> diff --git a/cpus.c b/cpus.c
>>>>>> index 82530c4..ae5ec99 100644
>>>>>> --- a/cpus.c
>>>>>> +++ b/cpus.c
>>>>>> @@ -398,6 +398,7 @@ static void do_vm_stop(RunState state)
>>>>>> vm_state_notify(0, state);
>>>>>> qemu_aio_flush();
>>>>>> bdrv_flush_all();
>>>>>> + bdrv_invalidate_cache_all();
>>>>>> monitor_protocol_event(QEVENT_STOP, NULL);
>>>>>> }
>>>>>
>>>>> This is too much. Reopening all qcow2 images each time that we stop the
>>>>> vm looks excesive, no?
>>>>
>>>> This general code came in via:
>>>>
>>>> http://mid.gmane.org/address@hidden
>>>>
>>>> That series made migration stable after issuing a stop operation. I
>>>> believe the justification was for debugging purposes or something like
>>>> that.
>>>>
>>>> At any rate, invalidating the cache is part of what's required to make
>>>> things stable. If you look at something like cache=unsafe, the only
>>>> way the metadata will get flushed if via a bdrv_close since bdrv_flush
>>>> is a nop.
>>>>
>>>> So this is needed as long as we care about supporting this use-case.
>>>
>>> Then we need a "proper" qcow2 invalidate call. Doing in qemu toplevel:
>>>
>>> (qemu)stop
>>>
>>> And now all your qcow2 block devices are closed, or perhaps failing to
>>> re-open() looks too much to me (TM).
>>>
>>> Kevin?
>>
>> Look closely at the patch. It doesn't actually close()/open() anything.
Sorry, someday I will remember the difference between bdrv_open() and
bdrv_file_open().
>> It just invokes the bdrv_close() routine which calls the free functions on
>> the
>> l1/l2 caching functions. bdrv_open() doesn't actually open anything (it
>> assumes
>> the file is already open. It just reads the header and metadata over again.
>>
>> For something that's basically a hack, it turned out to work very cleanly :-)
>
> But why do we need to do it on stop?
>
> I don't think it makes even sense logically: bdrv_invalidate_cache()
> means "throw all your caches away and refetch everything from disk".
> What do we gain from doing this on stop? To some degree I could
> understand if you did it on cont, so that you can modify an image on the
> host while the VM is stopped (though I would still consider it criminal
> :-)).
Fully agree. When I answered, I was thinking that I "could" want it on
"cont", just to be able to do evil things. But I thought it was
"criminal" just to write the idea O:-)
Later, Juan.
- [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2), (continued)
- [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2), Anthony Liguori, 2011/11/12
- Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2), Juan Quintela, 2011/11/14
- Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2), Anthony Liguori, 2011/11/14
- Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2), Juan Quintela, 2011/11/14
- Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2), Anthony Liguori, 2011/11/14
- Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2), Kevin Wolf, 2011/11/14
- Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2), Anthony Liguori, 2011/11/14
- Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2), Juan Quintela, 2011/11/14
- Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2), Kevin Wolf, 2011/11/14
- Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2), Anthony Liguori, 2011/11/14
- Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2),
Juan Quintela <=
[Qemu-devel] [PATCH 6/7] qcow2: implement bdrv_invalidate_cache, Anthony Liguori, 2011/11/12
[Qemu-devel] [PATCH 4/7] qed: add migration blocker, Anthony Liguori, 2011/11/12
[Qemu-devel] [PATCH 7/7] qcow2: relax migration blocker, Anthony Liguori, 2011/11/12
Re: [Qemu-devel] [PATCH 1/7] migrate: add migration blockers, Kevin Wolf, 2011/11/14
Re: [Qemu-devel] [PATCH 1/7] migrate: add migration blockers, Kevin Wolf, 2011/11/14
Re: [Qemu-devel] [PATCH 1/7] migrate: add migration blockers, Juan Quintela, 2011/11/14
[Qemu-devel] [PATCH 1/7] migrate: add migration blockers, Anthony Liguori, 2011/11/12