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From: Eric Blake <eblake@redhat.com>
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Date: Wed, 2 May 2018 10:19:03 -0500
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Subject: Re: [Qemu-devel] [PATCH] qemu-img: return allocated size for block
 device with qcow2 format
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To: Max Reitz <mreitz@redhat.com>, Ivan Ren <renyime@gmail.com>, qemu-devel@nongnu.org
Cc: kwolf@redhat.com, qemu-block@nongnu.org

On 05/02/2018 10:13 AM, Max Reitz wrote:

>> We also recently added 'qemu-img measure', which DOES report how many
>> clusters are in use.=C2=A0 Is any of that reusable here?
>=20
> It only tells you that information for a hypothetical new image, though=
,
> doesn't it?

It has two uses: with just a size, estimate the overhead needed to=20
create a file with the given format and exposing the given size to the=20
guest (both sparse and fully allocated sizes are estimated); and with a=20
pre-existing image, compute the exact overhead needed for 'qemu-img=20
convert' to create a new image with the given format and the same=20
guest-visible contents.  The latter use, where it uses an existing guest=20
image as the starting point to measure, indeed only tells you what a=20
hypothetical new image will occupy (the used cluster count, not the=20
wr_highest_offset count) - but isn't that what you want?

--=20
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org