[libvirt] Why "integratorcp" as the default machine type for ARM / AArch64?

[Kashyap Chamarthy]

On Mon, Nov 26, 2018 at 01:08:20PM +0100, Andrea Bolognani wrote:
> On Mon, 2018-11-26 at 12:51 +0100, Kashyap Chamarthy wrote:
> > On Mon, Nov 26, 2018 at 12:29:45PM +0100, Andrea Bolognani wrote:
> > > The entries in the table are supposed to reflect the (historical)
> > > QEMU default; in the case of Arm architectures, you're correct that
> > > integratorcp is not the right value, but it should *not* be virt:
> > 
> > Right, I keep remembering this on-and-off---there is no default machine
> > type for ARM architectures, and that it depends on the CPU model
> > configured.
> 
> I don't think it depends on the CPU model at all: you are just
> supposed to provide one explicitly every single time.

Oops, you're right.  It is the other way around: the default *CPU* type
depends on the board model (i.e. machine type) for ARM / AArch64.  

And speaking of which, as Peter Maydell put it on IRC once: "some board
models will ignore any user specificed CPU type; some will error out if
you pick one it can't handle; some will silently try to use it and may
be functional or may  not" :-)

> > > QEMU simply has no default for those architectures, so we should set
> > > the entires above to NULL and let libvirt go through the usual
> > 
> > Can send that trivial patch, if someone is already not on it.
> 
> I have a patch ready, so you can save the effort; additionally,
> regardless of who sends the patch I would like Dan to review it to
> make sure I didn't miss anything in my reasoning :)

Thanks!

> > > process of looking for QEMU's default machine type, not finding one,
> > > and falling back to using the first entry in the list (on my system
> > > that would be akita).
> 
> Small correction: the list from which libvirt will choose the first
> item as fallback is *not* the output of 'qemu -machine help' but
> rather the result of running the 'query-machines' QMP command.

Ah, right; I should've also tried the QMP.  Makes sense.

Thanks for the clarification.

> At least on my system, that will once again result in integratorcp
> being picked as the default, only it will have been obtained through
> the correct route this time.

-- 
/kashyap