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Re: [Qemu-devel] [PATCH v3] qemu-img: Implement 'diff' operation.

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH v3] qemu-img: Implement 'diff' operation.
Date: Mon, 21 May 2012 16:06:29 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1

Am 21.05.2012 15:59, schrieb Richard W.M. Jones:
> On Mon, May 21, 2012 at 03:29:22PM +0200, Kevin Wolf wrote:
>> Am 17.05.2012 17:34, schrieb Richard W.M. Jones:
>>> From: "Richard W.M. Jones" <address@hidden>
>>> This produces a qcow2 file which is the difference between
>>> two disk images.  ie, if:
>>>   base.img     - is a disk image (in any format)
>>>   modified.img - is base.img, copied and modified
>>> then:
>>>   qemu-img diff -b base.img modified.img diff.qcow2
>>> creates 'diff.qcow2' which contains the differences between 'base.img'
>>> and 'modified.img'.  Note that 'diff.qcow2' has 'base.img' as its
>>> backing file.
>>> Signed-off-by: Richard W.M. Jones <address@hidden>
>>> Cc: Matthew Booth <address@hidden>
>>> Cc: Pablo Iranzo Gómez <address@hidden>
>>> Cc: Tomas Von Veschler <address@hidden>
>> Hm, I'm wondering... If I have a command line like this:
>>   qemu-img diff -b base.img modified.img diff.qcow2
>> Would this be equivalent to this sequence?
>>   qemu-img create -f qcow2 -b modified.img diff.qcow2
>>   qemu-img rebase -b base.img diff.qcow2
>> Or is there some detail that I'm missing? If it is equivalent, this
>> would suggest that either the new command isn't necessary at all or at
>> least that it should reuse the qemu-img rebase code.
> Yes.  I tried for a while to work out the sequence of commands that
> could make a diff using 'qemu-img rebase', but it wasn't obvious and I
> gave up.  It should at least be documented.  How about the attached
> patch?

Looks good to me. As it already has a SoB, I've applied it to the block
branch. Let me know if I should dequeue it again.


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