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Re: [Qemu-devel] [PATCH v2 02/10] block: set snapshot option for block d
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v2 02/10] block: set snapshot option for block devices in blkreplay module |
Date: |
Fri, 16 Sep 2016 11:49:45 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 |
On 16/09/2016 11:36, Pavel Dovgalyuk wrote:
>> From: Paolo Bonzini [mailto:address@hidden On Behalf Of Paolo Bonzini
>> On 16/09/2016 09:55, Pavel Dovgalyuk wrote:
>>>> Since you have to create
>>>> overlay.qcow2 outside QEMU anyway, overlay.qcow2 might as well be the
>>>> "image". That is, you could choose between:
>>>>
>>>> -drive driver=blkreplay,if=none,image=overlay.qcow2,id=img-blkreplay \
>>>> -rr snapshot=replay_init,...
>>>>
>>>> -drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay
>>>>
>>>> The temporary snapshot would be created if there's no "-rr snapshot" option
>>>> on the command line.
>>>>
>>>> Does this make sense?
>>>
>>> There are two different parts:
>>> - creating an overlay
>>> - creating the snapshot
>>>
>>> Overlay is needed to preserve the state of the original backing file.
>>> In the current version temporary overlay is always created at start of qemu.
>>
>> Yes, this would still be the default for rr mode.
>>
>>> I don't think that it is convenient forcing user to create overlay manually.
>>
>> Note that all I'm only saying that _only for the case where the user
>> creates the overlay manually anyway_ there is no need to specify both
>> image and overlay. (I also don't like particularly the hard-coded
>> snapshot name replay_init, which can be overridden by -loadvm but not
>> when saving).
>
> Ok, this seems reasonable to fix.
>
>>
>> So there are various possibilites:
>>
>> First proposal:
>>
>> - automatically created overlay is -icount rr=record|replay (then
>> snapshot name doesn't matter, it can be replay_init)
>>
>> - manually created overlay is -icount
>> rr=record|replay,rrsnapshot=snapname (then snapshot name matters because
>> you can have different snapshots in the same file)
>
> We can't create overlay with icount suboptions, because there could be several
> block devices. Each one needs its own overlay.
Right, so the overlay name is specified in each -drive option the
blkreplay image. rrsnapshot is just the name of the first snapshot that
is created (for rr=record, instead of requiring manual interaction with
the monitor) or loaded (for rr=replay; in this case it's a convenience
only).
Paolo
[Qemu-devel] [PATCH v2 04/10] replay: save/load initial state, Pavel Dovgalyuk, 2016/09/15
[Qemu-devel] [PATCH v2 05/10] replay: move internal data to the structure, Pavel Dovgalyuk, 2016/09/15
[Qemu-devel] [PATCH v2 06/10] replay: vmstate for replay module, Pavel Dovgalyuk, 2016/09/15
[Qemu-devel] [PATCH v2 07/10] replay: allow replay stopping and restarting, Pavel Dovgalyuk, 2016/09/15