On 20/09/2016 15:51, Pavel Dovgalyuk wrote:
>> From: Paolo Bonzini [mailto:pbonz...@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)
> Now I see.
> This seems ok, but:
>  - this approach adds some garbage to original disk image
>  - won't work with raw images

Yes, for raw images or if you want to keep the pristine image you have
to do a "qemu-img create -f qcow2 -b disk.raw foo.qcow2".


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