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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <f80b8906-c7bf-f9a7-adf0-7d981eebbc9a@redhat.com>
Date: Tue, 20 Sep 2016 15:45:07 +0200
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Subject: Re: [Qemu-devel] [PATCH v3 4/8] replay: save/load initial state
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To: Pavel Dovgalyuk <dovgaluk@ispras.ru>, 'Pavel Dovgalyuk' <pavel.dovgaluk@ispras.ru>, qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org, jasowang@redhat.com, quintela@redhat.com, mst@redhat.com, 'Kevin Wolf' <kwolf@redhat.com>



On 20/09/2016 15:37, Pavel Dovgalyuk wrote:
>> c) no rrsnapshot implies -snapshot:
>>    without overlay:
>>       -drive file=disk.raw,if=none,id=img-direct
>>       -drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay
>>
>>    with overlay:
>>      -drive file=foo.qcow2,if=none,id=img-direct
>>      -drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay
>>      -icount ...,rrsnapshot=snapname
> 
> But how record will create this overlay?
> This method requires creating overlay manually, because backing file is
> not specified at all.

You create it manually, or you just use a .qcow2 file to begin with for
your image.  Then:

1) if you specify no snapshot, a temporary .qcow2 file is created on top
so data is not destroyed

2) if you specify a snapshot, that snapshot is preserved (so you don't
lose the base state even though the file changes)

Paolo