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

[Andreas Färber]

Am 02.06.2010 um 16:12 schrieb Daniel P. Berrange:

> 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'.

Iiuc sparc and ppc try to follow the IEEE1275 OpenFirmware naming  
conventions. Those should not blindly be patched to some random  
convention just to make them more x86-like. OpenFirmware uses  
address@hidden on my ppc machine. In other places, e.g. disks, numbering  
appears to be done locally via @0, @1, etc. See `show-devs` for a  
complete listing.

As suggested by Paul there are device aliases, so that in `qemu-system- 
ppc -cdrom /dev/null` you can run `dev pci` followed by `pwd` to see  
the real device name.
Lacking a working `devalias`, see `dev /aliases .properties` for some  
more: screen, nvram, cd, cdrom, scca, sccb, adb-keyboard, adb-mouse

Andreas

> 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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