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Re: [libvirt] [PATCH] qemu: Do not unlink managedsave image if restoring fails.



On Wed, Apr 06, 2011 at 08:21:56AM -0600, Eric Blake wrote:
> On 04/06/2011 06:51 AM, Daniel Veillard wrote:
> > On Wed, Apr 06, 2011 at 05:02:36PM +0800, Osier Yang wrote:
> >> 于 2011年04月06日 16:50, Daniel Veillard 写道:
> >>> On Tue, Apr 05, 2011 at 08:55:01AM -0600, Eric Blake wrote:
> >>      Somehow this is true, but as we have API and virsh commands
> >> for snapshot specificly, is it fine to make a change on the virsh
> >> manual to tell the user about we remove the state file if restoring
> >> succeeded? I did that when doing v3 patch, :-)
> > 
> >   Still that can be considered a regression, that behaviour is the
> > same since the introduction of the API years ago, we can't change it now
> > just because we think it's cool.
> >   Document the fact that in general once the restore suceeded the
> > file should be removed since the data are unlikely to be reusable
> > without loss of integrity, but you can't change the behaviour.
> 
> What about this proposal, for being less severe?  If we can open the
> file read-write, then we modify it on a successful restore to change a
> bit to mark that the image is suspect.

  technically the beginning of the image is an XML dump of the domain
if I remember correctly, we could try to do something smart in there
to do the detection.

> Loading then looks for that bit,
> and fails to restore an image with the bit set unless you pass a --force
> option.

  That's still a regression, existing code using for example the LVM
for snapshot independantly of our API will still break.

> But I agree that since we have already got releases in the wild that do
> not delete the file, that we cannot change behavior to delete it at this
> point.

  Same for being able to restore, as there are legitimate uses. I would
be okay for a warning to be emitted if we detect a subsequent restore
but we cannot make the operation to fail by default in my opinion.

Daniel

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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