Re: [Qemu-devel] qcow2 snapshot + resize

[Kevin Wolf <kwolf@redhat.com>]

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Am 06.01.2016 um 17:30 hat Max Reitz geschrieben:
> On 06.01.2016 17:28, Eric Blake wrote:
> > On 01/06/2016 09:20 AM, Max Reitz wrote:
> > 
> >>> If I take a snapshot while the guest sees a 1G disk, then resize the
> >>> disk to 2G, then roll back to the point in time of the snapshot, I'd
> >>> expect the disk to roll back to 1G in size.  Anything else is likely to
> >>> confuse the guest.  And that's what current resize support already does
> >>> (it only resizes the active image, not the snapshots).
> >>
> >> No, the current resize operation just refuses to resize the image if it
> >> has any snapshots. Snapshots currently do not store the size of the
> >> image when they were created.
> > 
> > Huh? I thought that we specifically added bytes 48-55 per snapshot entry
> > in the qcow2v3 description specifically so that internal snapshots DO
> > record the size of the image when the snapshot was created.
> 
> Oh, you're right! Well, then that was probably the intention, yes.
> However, resizing an image with snapshots will still fail.

I guess the only thing that would need to implement something new is
qcow2_snapshot_goto(), which currently refuses to load a snapshot that
has a different disk size.

Once this is done, just removing the check in qcow2_truncate() should be
okay.

Kevin

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