Re: [Qemu-devel] [PATCH V4 2/9] snapshot: add paired functions for internal snapshot id and name

[Wenchao Xia]

于 2013-7-10 22:22, Kevin Wolf 写道:
> Am 10.07.2013 um 15:54 hat Wenchao Xia geschrieben:
> > 于 2013-7-10 21:10, Kevin Wolf 写道:
> > > Am 08.07.2013 um 10:00 hat Wenchao Xia geschrieben:
> > > > Internal snapshot's ID and name concept are both visible in general
> > > > block level, they are observed by user in "info snapshots", so it is
> > > > possible to have conflict. Although we can separate the two concept in
> > > > programming, but if they can be distinguished in string itself, things
> > > > will be simple and clear, so introduce two functions to do it.
> > > >
> > > > The implemention, qcow2 snapshot calls snapshot_id_string_generate() to
> > > > make sure it follows the rule in driver. If caller or user give a check
> > > > with snapshot_name_wellformed() before create snapshot, then the ID
> > > > and name will never conflict. The check can be also taken in
> > > > qcow2_snapshot_create(), but require it to return error reason.
> > >
> > > I'm not sure how useful this is. While we can restrict what IDs we allow
> > > for creating new snapshots, we cannot take any advantage from it because
> > > existing snapshots could already be named with only digits (they could
> > > also use a non-numeric ID). At the end of the day we're limiting the
> >    Qcow2's ID seems always numeric, do you mean sheepdog may have
> > non-numeric ID?
>
> That's not true, qcow2 has an ID string rather than a numeric ID.
  But there is no way to specify non-numeric ID in public interface,
such as savevm, qemu-img, and in qcow2_snapshot_create(),
find_new_snapshot_id() will always fill in a numeric ID string, so
result is that, qcow2's snapshot ID string is always a numeric string.

> > > choice of IDs that can be generated with the QMP command without a real
> > > reason.
> >    This patch may limit the choice of snapshot name. Maybe we can't
> > benefit from it now because existing code, but shouldn't it be improved
> > in any new interface to alleviate the problem? I guess you idea
> > is drop this check in the new interface, isn't it?
>
> Well, the thought is that limiting it in QMP is of no use if there is no
> corresponding limitation in the backend. So yes, I think, as long as
> block drivers can deal with numeric snapshots names, QMP should allow
> dealing with them.
  OK, I'll drop this limit.

> Kevin


--
Best Regards

Wenchao Xia