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

[Michael S. Tsirkin]

On Fri, Oct 12, 2012 at 09:27:02AM +0200, Gerd Hoffmann wrote:
>   Hi,
> 
> >> Yes. Reason I ask is because q35 is adding bridges by default now.
> >> Would it be possible to only add them if requested on command line by user
> >> instead? I realize some guests expect devices at specific slots
> >> but this does not apply to bridges I think?
> > 
> > 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.

> > So 'lspci' goes from:
> > 
> > 00:00.0 Host bridge: Intel Corporation 82G33/G31/P35/P31 Express DRAM 
> > Controller
> 
> Keep.
> 
> > 00:01.0 PCI bridge: Intel Corporation 5500 Non-Legacy I/O Hub PCI Express 
> > Root Port 0 (rev 02)
> 
> That looks bogous.  Drop.
> 
> > 00:02.0 VGA compatible controller: Cirrus Logic GD 5446
> 
> Our default vga.
> 
> > 00:03.0 Ethernet controller: Intel Corporation 82540EM Gigabit Ethernet 
> > Controller (rev 03)
> 
> 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. And it's not really e1000 at all.
Fact is, we don't emulate real hardware exactly.
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.

-- 
MST