Re: [Qemu-devel] [PATCH v2 0/3] HMP/snapshot changes - do not use ID anymore

[Kevin Wolf]

Am 09.01.2019 um 18:55 hat Eric Blake geschrieben:
> On 1/9/19 11:38 AM, Max Reitz wrote:
> 
> >>>>> I do think it affects users of HMP, because right now you can delete
> >>>>> snapshots with their ID, and after this series you cannot.
> >>>>
> 
> >> This. Is. HMP.
> >>
> >> Not a stable ABI, no deprecation period of two releases.
> > 
> > Well, if you want to do it.
> > 
> > This may be HMP, but this is also the only interface to savevm, so it's
> > not like users have a choice to use a more stable interface.  I know
> > that was a conscious decision, more or less, but I don't see why we need
> > to be so nasty when the hardest thing about doing a nice deprecation
> > would be to remember to make it an error in half a year.
> 
> Indeed, and libvirt IS using 'savevm' via HMP via QMP's
> human-monitor-command, since there is no QMP counterpart for internal
> snapshot.  Even though lately we consistently tell people that internal
> snapshots are underdeveloped and you should use external snapshots, it
> does not get away from the fact that libvirt has been using 'savevm' to
> drive internal snapshots for years now, and that we MUST consider
> back-compat and/or add an introspectible QMP interface before making
> changes that would break libvirt.

Okay, so what does libvirt do when you request a snapshot with a
numerical name? Without having looked at the code, the best case I would
expect that it forbids them, and more realistically I suspect that we
may actually fix a bug for libvirt by changing the semantics.

Or does libvirt really use snapshot IDs rather than names?

Kevin

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