Re: [PATCH v2 (BROKEN) 0/6] migration: bring improved savevm/loadvm/delvm to QMP

[Markus Armbruster]

Kevin Wolf <kwolf@redhat.com> writes:

> Am 28.08.2020 um 08:20 hat Markus Armbruster geschrieben:
>> Kevin Wolf <kwolf@redhat.com> writes:
>> 
>> > Am 27.08.2020 um 13:06 hat Markus Armbruster geschrieben:
>> >> Daniel P. Berrangé <berrange@redhat.com> writes:
>> >> 
>> >> > On Wed, Aug 26, 2020 at 07:28:24PM +0100, Daniel P. Berrangé wrote:
>> >> >> On Wed, Aug 26, 2020 at 05:52:06PM +0200, Markus Armbruster wrote:
>> >> >> > Open questions:
>> >> >> > 
>> >> >> > * Do we want the QMP command to delete existing snapshots with
>> >> >> >   conflicting tag / ID, like HMP savevm does?  Or do we want it to 
>> >> >> > fail
>> >> >> >   the transaction?
>> >> >> 
>> >> >> The intent is for the QMP commands to operate exclusively on
>> >> >> 'tags', and never consider "ID".
>> >> >
>> >> > I forgot that even HMP ignores "ID" now and works exclusively in terms
>> >> > of tags since:
>> >> >
>> >> >
>> >> >   commit 6ca080453ea403959ccde661030ca16264acc181
>> >> >   Author: Daniel Henrique Barboza <danielhb413@gmail.com>
>> >> >   Date:   Wed Nov 7 11:09:58 2018 -0200
>> >> >
>> >> >     block/snapshot.c: eliminate use of ID input in snapshot operations
>> >> 
>> >> Almost a year after I sent the memo I quoted.  It's an incompatible
>> >> change, but nobody complained, and I'm glad we got this issue out of the
>> >> way.
>> >
>> > FWIW, I would have ignored any complaint about incompatible changes in
>> > HMP. It's not supposed to be a stable API, but UI.
>> 
>> The iffy part is actually the loss of ability to access snapshots that
>> lack a name.  Complaints about that would have been valid, I think.
>> Fortunately, there have been none.
>
> 'loadvm ""' should do the trick for these.

As long as you have at most one.

>                                            The same way as you have to
> use with 'savevm' to create them in non-prehistoric versions of QEMU.
> We stopped creating snapshots with empty names by default in 0.14, so
> they are probably not very relevant any more. (Versioned machine types
> go back "only" to 1.0, so good luck loading a snapshot from an older
> version. And I wouldn't bet money either on a 1.0 snapshot still working
> with that machine type...)

No argument.