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

2013-05-27 Thread Stefan Hajnoczi 
On Sat, May 25, 2013 at 08:29:11AM -, 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

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

2013-05-25 Thread Michael Coppola 
Public bug reported:

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.

I found a lot of discussion about this topic on the mailing list years
ago, including some patch submissions, but none of the conversations
panned out.

http://lists.gnu.org/archive/html/qemu-discuss/2011-10/msg00011.html
http://copilotco.com/mail-archives/qemu.2008/msg00072.html
http://web.archiveorange.com/archive/v/1XS1vcusGInZKG2e0ImX
http://marc.info/?l=qemu-develm=117191084713590

What would it take for this feature to be added, and can we use the
patches submitted by Eddie Kohler to enable this feature?

** Affects: qemu
 Importance: Undecided
 Status: New

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https://bugs.launchpad.net/bugs/1184089

Title:
  [Feature request] loadvm snapshot as read-only

Status in QEMU:
  New

Bug description:
  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.

  I found a lot of discussion about this topic on the mailing list years
  ago, including some patch submissions, but none of the conversations
  panned out.

  http://lists.gnu.org/archive/html/qemu-discuss/2011-10/msg00011.html
  http://copilotco.com/mail-archives/qemu.2008/msg00072.html
  http://web.archiveorange.com/archive/v/1XS1vcusGInZKG2e0ImX
  http://marc.info/?l=qemu-develm=117191084713590

  What would it take for this feature to be added, and can we use the
  patches submitted by Eddie Kohler to enable this feature?

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