Re: [Qemu-devel] [PATCH] Name the default PCI bus "pci.0" on all architectures

["Daniel P. Berrange" <berrange@redhat.com>]

On Fri, May 28, 2010 at 08:39:53PM +0100, Paul Brook wrote:
> > The system emulators for each arch are using inconsistent
> > naming for the default PCI bus "pci" vs "pci.0". Since it
> > is conceivable we'll have multiple PCI buses in the future
> > standardize on "pci.0" for all architectures. This ensures
> > mgmt apps can rely on a name when assigning PCI devices an
> > address on the bus using eg '-device e1000,bus=pci.0,addr=3'
> 
> No. Bus names are local to the parent device.  None of the host bridges 
> support multiple bridges, so the ".0" suffix makes no sense.  The parent 
> device has no idea whether it owns the "default" pci bus or not.
> If you have multiple PCI busses then you can identify them by the device 
> path.

The problem is that the ID names of default devices in machines are ABI
sensitive. Management apps need to know what the ID of these default
devices are. The x86 machines have already used 'pci.0' as their name
in the previous 0.12 release and libvirt is using this naming. We later
discovered many non-x86 archs have a name of just 'pci'. We need a single
consistent naming across all arches, hence this patch whcih standardizes
on 'pci.0'. The '.N' convention is used extensively in QEMU and is more 
futureproof as & when QEMU supports multiple buses, without requiring 
apps to use the more verbose device paths to ensure uniquness.

Daniel
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