Re: [Qemu-devel] [Bug 1184089] [NEW] [Feature request] loadvm snapshot as read-only

[Stefan Hajnoczi <stefanha@gmail.com>]

On Sat, May 25, 2013 at 08:29:11AM -0000, Michael Coppola wrote:
> There are many ways to take and manage snapshots in QEMU, but one main
> feature that's missing is the ability to 'loadvm' a LIVE snapshot and
> have all future changes redirected to a temporary file.  This would
> effectively be combining the -loadvm and -snapshot switches and make the
> snapshot read-only.  With this feature, users would be provided a
> "sandbox" and be able to start and restart the same live snapshot
> without corrupting the image in doing so.

This should be possible soon.  Wenchao Xia is working on new monitor
commands that allow you to combine internal snapshots (loadvm/savevm)
with external snapshots (blockdev-snapshot-sync).

You would submit a QMP 'transaction' command that specifies a loadvm
followed by a blockdev-snapshot-sync.  This operation is atomic.

Note that internal snapshots do not destroy the snapshot.  Therefore,
when you loadvm an internal snapshot and write to the disk, you are not
modifying the internal snapshot only the current state of the disk.  You
can loadvm it again later.

Stefan