Re: [Qemu-devel] [PATCH] Correctly assign PCI domain numbers

[David Gibson <david@gibson.dropbear.id.au>]

On Mon, Aug 01, 2011 at 01:10:38PM +0300, Michael S. Tsirkin wrote:
> On Mon, Aug 01, 2011 at 04:51:02PM +1000, David Gibson wrote:
> > qemu already almost supports PCI domains; that is, several entirely
> > independent PCI host bridges on the same machine.  However, a bug in
> > pci_bus_new_inplace() means that every host bridge gets assigned domain
> > number zero and so can't be properly distinguished.  This patch fixes the
> > bug, giving each new host bridge a new domain number.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> 
> OK, but I'd like to see the whole picture.
> How does the guest detect multiple domains,
> and how does it access them?
> 
> > ---
> >  hw/pci.c |    5 ++++-
> >  1 files changed, 4 insertions(+), 1 deletions(-)
> > 
> > diff --git a/hw/pci.c b/hw/pci.c
> > index 36db58b..2b4aecb 100644
> > --- a/hw/pci.c
> > +++ b/hw/pci.c
> > @@ -262,6 +262,8 @@ int pci_find_domain(const PCIBus *bus)
> >      return -1;
> >  }
> >  
> > +static int pci_next_domain; /* = 0 */
> > +
> >  void pci_bus_new_inplace(PCIBus *bus, DeviceState *parent,
> >                           const char *name,
> >                           MemoryRegion *address_space,
> > @@ -274,7 +276,8 @@ void pci_bus_new_inplace(PCIBus *bus, DeviceState *parent,
> >  
> >      /* host bridge */
> >      QLIST_INIT(&bus->child);
> > -    pci_host_bus_register(0, bus); /* for now only pci domain 0 is supported */
> > +
> > +    pci_host_bus_register(pci_next_domain++, bus);
> 
> What happens when that overflows?

Well, I guess we get an overlap, and therefore multiple domains with
the same number.

So, exactly what happens now, only four billion times less often.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson