Re: [PATCH RFC] migration: warn about non-migratable configurations unless '--no-migration' was specified

[Markus Armbruster]

Eduardo Habkost <ehabkost@redhat.com> writes:

[...]
> 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.
>
> - REQUIRED: live migration is required, and adding a migration
>   blocker would be a fatal error.

To be precise: would be an error.  During initial configuration, the
error is fatal, i.e. exit(1).  In a QMP command, it's not; only the
command fails.

>   This is already implemented by --only-migratable.
>   I suggest making this the default on versioned machine types
>   after a few releases, and after deprecating UNKNOWN.

Makes sense to me (but of course we can still quibble about the names).