Re: [PATCH v2] hw/i386: disable smbus migration for xenfv

[Paolo Bonzini]

On 27/01/20 14:26, Olaf Hering wrote:
>> That's years away, so ideally libxl would have migrated away from
>> xenfv before that.  For now, sticking to a fixed version as in
>> Olaf's patch is a good stopgap measure.
> Is there a way to inspect a running qemu process to see what version
> it is? I assume one thing is to poke at /proc/$PID/cmdline and make
> some guesses. Would a running qemu report what pc-i440fx it supports?

Yes, via QMP. For example on QEMU 3.1 with "-M pc" you would get:

{"execute":"qom-get",
 "arguments":{"path":"/machine", "property":"type"}}
{"return": "pc-i440fx-3.1-machine"}

So libxl would start QEMU with "-M pc,accel=xen -device xen-platform"
when _not_ migrating, but on the destination of live migration it would
query the machine type and use "-Mpc-i440fx-3.1,accel=xen -device
xen-platform".

A cleaner possibility is to do {"execute": "query-machines"} and search
the result for an entry like

{"hotpluggable-cpus": true,
 "name": "pc-i440fx-3.1", "is-default": true, "cpu-max": 255,
 "alias": "pc"}

i.e. the name corresponding to the entry with "alias": "pc" would be
used on the destination.

Thanks,

Paolo

> With such info an enlightened libxl might be able construct a
> compatible commandline for the receiving host.