Re: [Qemu-devel] [PATCH v2 21/21] q35: add acpi-based pci hotplug.

[Jason Baron]

On Fri, Oct 12, 2012 at 12:06:44PM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> >>> I just tried out getting rid of the bridges by default.
> >>
> >> That clearly raises the question which devices should be created
> >> automatically by -M q35.  I think the devices which are part of the ich9
> >> chipset should be there by default.  /me looks at my laptop which
> >> happens to have a ich9 chipset.
> > 
> > The reason this is a bad idea is very simple: we only have a way to add
> > devices not to remove them.  So if you miss a device which your guest
> > needs, it is easy to add, but there is no way to remove.
> 
> Why would you want remove devices?  They don't harm when present.  And
> you can't remove them on real hardware either.  Try ordering a ich9
> without sound or usb ;)
> 
> >> Real ich9 has the e1000 @ 00:19.0, so it would make sense to place one
> >> there.  Adding a default nic will probably create some headache though,
> >> so maybe better don't.
> > 
> > And that's just one example.
> 
> It is problematic because the nic needs configuration and configuring a
> builtin device is tricky.  Also our e1000 model isn't the ich9 one.
> 
> Most other chipset devices are not problematic at all as they are just
> controllers where you can attach stuff to (and by default there isn't
> anything attached).  This includes:
> 
>   * pcie ports (waiting for pcie devices plugged in).
>   * ahci controller (waiting for disks/cdroms being attached).
>   * intel-hda (waiting for audio coded (hda-*) being attached).
>   * ehci+uhci (waiting for usb devices being plugged in).
> 
> The stuff being attached/plugged there needs configuration, but not the
> controllers themself.
> 
> > Fact is, we don't emulate real hardware exactly.
> 
> But we try to.
> 
> > So let's have a minimal machine and if you want to add e1000 audio etc,
> > you can do this. We can even teach management to do it with friendly
> > UI as opposed to cryptic machine types.
> 
> /me disagrees.
> 

What if we have a 'basic' configuration as Michael suggests, but have an
easy way to specify that we want these additional built-in
controllers/bridges at their default slot.

For example, for q35 I can currently pass '-usb' and it will create a
uhci at slot 1d func 0. (I have small patch to add ehci as well).

Not sure if we have appropriate options we can piggy-back on for default
sound and bridges, but we can add these later, if this makese sense.

Thanks,

-Jason