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Subject: Re: [Qemu-devel] Can I only commit from active image to
 corresponding range of its backing file by qemu cmd?
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To: Eric Blake <eblake@redhat.com>, lampahome <pahome.chen@mirlab.org>, QEMU Developers <qemu-devel@nongnu.org>, Qemu-block <qemu-block@nongnu.org>, Markus Armbruster <armbru@redhat.com>

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From: Max Reitz <mreitz@redhat.com>
To: Eric Blake <eblake@redhat.com>, lampahome <pahome.chen@mirlab.org>,
 QEMU Developers <qemu-devel@nongnu.org>, Qemu-block <qemu-block@nongnu.org>,
 Markus Armbruster <armbru@redhat.com>
Message-ID: <81bba910-3e33-376d-f490-151fcccd4322@redhat.com>
Subject: Re: [Qemu-devel] Can I only commit from active image to corresponding
 range of its backing file by qemu cmd?
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On 13.09.18 20:37, Max Reitz wrote:

[...]

> Or, we would have to use backing=3Dnull, but for some reason that doesn=
't
> work.  I'll have to investigate.

Turns out this was fixed in e59a0cf17b1b9932b65e6fc25d6856976f5e4831.

(Why does Fedora still have only qemu 2.11?)

> So rebase will need to do:
>=20
> $ qemu-img rebase -u -b '' img.003
>=20
> $ qemu-img convert -O qcow2 \
>     "json:{'driver':'raw','offset':0,'size':1048576,\
>            'file':{'driver':'qcow2',\
>                    'file':{'driver':'file','filename':'img.003'}}}" \
>     "json:{'driver':'null-co','size':2097152}" \
>     img.003.commit.000
>=20
> $ qemu-img convert -O qcow2 \
>     "json:{'driver':'null-co','size':1048576}" \
>     "json:{'driver':'raw','offset':1048576,'size':2097152,\
>            'file':{'driver':'qcow2',\
>                    'file':{'driver':'file','filename':'img.003'}}}" \
>     img.003.nocommit

So starting with 2.12, putting a "'backing':null" behind
"'driver':'qcow2," will work just as well as rebasing img.003.

Max


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