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

[Michael S. Tsirkin]

On Wed, Aug 03, 2011 at 11:13:15AM +0100, Stefan Hajnoczi wrote:
> 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 <address@hidden>
> > 
> > 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?
> 
> In what scenario do we reach such a high number?  (I'm not saying this
> is harmless, just trying to understand if it should be an assert or
> error return.)
> 
> Stefan

Can bus ever get hot-plugged?