* Eduardo Habkost (ehabk...@redhat.com) wrote:
> On Mon, Apr 19, 2021 at 07:47:34PM +0100, Dr. David Alan Gilbert wrote:
> > * Daniel P. Berrangé (berra...@redhat.com) wrote:
> > > On Mon, Apr 19, 2021 at 06:15:56PM +0100, Daniel P. Berrangé wrote:
> > > > On Mon, Apr 19, 2021 at 06:11:47PM +0100, Dr. David Alan Gilbert wrote:
> > > > > * Eduardo Habkost (ehabk...@redhat.com) wrote:
> > > > > > I would make live migration policy an enum, just to make sure
> > > > > > we are explicit about the requirements:
> > > > > >
> > > > > > - UNKNOWN: this is the current state in QEMU 6.0, where we don't
> > > > > > really know what the user expects.
> > > > > > This can be the default on existing versioned machine types,
> > > > > > just for compatibility.
> > > > > > I suggest making this print warnings for every migration
> > > > > > blocker (like this patch does).
> > > > > > I suggest deprecating this behavior as soon as we can.
> > > > > >
> > > > > > - PREFERRED: try to make the VM migratable when possible, but
> > > > > > don't print a warning or error out if migration is blocked.
> > > > > > This seems to be the behavior expected by libvirt today.
> > > > > >
> > > > > > - NOT_NEEDED: live migration is not needed, and QEMU is free to
> > > > > > enable features that block live migration or change guest ABI.
> > > > > > We can probably make this the default on machine types that
> > > > > > never supported live migration.
> > > > >
> > > > > I suggest you could do this by adding:
> > > > > -warn-none-migratable
> > > > > -no-warn-none-migratable
> > > > >
> > > > > and then argue about defaults another time.
> > > >
> > > > If we're going to add new args, lets at least future proof our
> > > > approach with an extensible option that we can wire into QMP
> > > > too later
> > > >
> > > > -migratable none|preferred|required
> > > >
> > > > and letting us add extra key/value pairs to tune it if desired.
> > >
> > > Having said that, we potentially don't need a dedicated arg if we
> > > just make 'migratable=none|preferred|required' be a property of
> > > the machine type and hook everything off that
> >
> > I think my only difficulty with that is that I don't find any of those
> > 3 words 'obvious'.
>
> Any suggestions of replacements for those 3 words?
>
> Would the descriptions below be enough to clarify their meaning
> in documentation?
I prefer things that are fairly obvious without needing to look at the
documentation until you want the detail.
> - NONE: live migration is not needed, and device or machine code
> is allowed to enable features that block live migration or
> change guest ABI.
> (Not implemented yet)
>
> - PREFERRED: machine and device code should try to make the VM
> migratable when possible, but won't emit a warning or error out
> if migration is blocked.
> (Current default behavior)
>
> - REQUIRED: live migration support is required, and adding a
> migration blocker will be an error.
> (Implemented today by --only-migratable)
How about
-migratable blocked
Live migration is not allowed; an outbound migration will fail
-migratable allowed
Live migration is allowed, but some devices/options may block
it if they're unable to migrate [current default]
-migratable warn
Live migration is allowed, but if some device/option is
unable to migrate, migration will be blocked and a warning
printed
-migratable required
Live migration is allowed, attempting to add a device or
enable an option that can't migrate will fail. [--only-migratable]
Dave
> --
> Eduardo
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
