Re: [Qemu-devel] [PATCH 04/13] qdev: add generic qdev_device_add()

[Paul Brook <paul@codesourcery.com>]

On Friday 10 July 2009, Gerd Hoffmann wrote:
> On 07/10/09 19:23, Paul Brook wrote:
> > On Friday 10 July 2009, Gerd Hoffmann wrote:
> >> Will be used for -device command line.
> >
> > I think this is going in the wrong direction. The device tree provides us
> > with a standard way of identifying which bus to add a device to. We
> > should be removing uses of pci_create, not adding new ones.
>
> Why?
>
> Let me guess: Because pci bus numbers are guest-changeable and thus not
> stable?

Because I don't think this code need to be bus specific.

> How about using user-specified ids to specify busses then?
>
>PCI example:
>   instead of  -device $name,addr=$bus:$slot.$fn
>   use         -device $name,bus=root,addr=$slot.$fn
>
>SCSI example:
>   host adapter:  -device lsi,id=foo
>   scsi disk:     -device scsi-disk,bus=foo,addr=$lun

I was thinking something a bit more like

  -device lsi,bus=/i440fx/pci
  -device scsi-disk,bus=/i440fx/pci/lsi/scsi

This example is maybe slightly unclear because the i440fx and lsi child busses 
happen to be called "pci" and "scsi". For devices with multiple child busses 
they may have different names.

Adding some form of aliases may be convenient. For example the pci machine 
could alias "pci0" to "/i440fx/pci", which would give 
  -device lsi,bus=pci0
  -device scsi-disk,bus=pci0/lsi/scsi

We also need to figure out the naming of multiple similar devices on the same 
bus. Possibly your "device id" could be used to identify devices on a bus. 
e.g. if we wanted two scsi adapters:

 -device lsi,bus=pci0,id=foo
 -device lsi,bus=pci0,id=bar
 -device scsi-disk,bus=pci0/foo/scsi
 -device scsi-disk,bus=pci0/bar/scsi

Paul