Re: [Qemu-devel] Re: [PATCH] PCI: Bus number from the bridge, not the device

[Michael S. Tsirkin]

On Mon, Nov 22, 2010 at 04:58:11PM +0200, Gleb Natapov wrote:
> On Mon, Nov 22, 2010 at 04:56:16PM +0200, Michael S. Tsirkin wrote:
> > On Mon, Nov 22, 2010 at 04:52:32PM +0200, Gleb Natapov wrote:
> > > On Mon, Nov 22, 2010 at 04:50:29PM +0200, Michael S. Tsirkin wrote:
> > > > On Mon, Nov 22, 2010 at 03:04:51PM +0200, Gleb Natapov wrote:
> > > > > On Mon, Nov 22, 2010 at 10:16:57AM +0200, Michael S. Tsirkin wrote:
> > > > > > On Mon, Nov 22, 2010 at 09:37:07AM +0200, Gleb Natapov wrote:
> > > > > > > > > > It's probably required to make them stable anyway.
> > > > > > > > > > 
> > > > > > > > > Why?
> > > > > > > > 
> > > > > > > > To avoid bus renumbering on reboot after you add a pci-to-pci 
> > > > > > > > bridge.
> > > > > > > > 
> > > > > > > Why should qemu care?
> > > > > > 
> > > > > > Stable bus numbering is a feature *users* care about, because
> > > > > > some Guest OSes get confused when a card gets moved to another
> > > > > > bus.
> > > > > > 
> > > > > So if user cares about it it should not change HW configuration of 
> > > > > QEMU.
> > > > > I guess those OSes knows how to handle hot-pluggable equipment 
> > > > > otherwise
> > > > > they will get confused on real HW too. Why QEMU should care to 
> > > > > preserve
> > > > > something in a face of configuration change?
> > > > > 
> > > > > --
> > > > >                       Gleb.
> > > > 
> > > > We've been there, weren't we? See
> > > > http://fedoraproject.org/wiki/Features/KVM_Stable_PCI_Addresses#KVM_Stable_PCI_Addresses
> > > > 
> > > This is about stable HW configuration.
> > 
> > Exactly. We have the same need for nested bridges and devices behind
> > them.
> > 
> And now you are talking about topology, not guest assigned bus numbers.

I suspect that if bus numbers change, it has the same effect as topology
change on the guest. Need to test though, I'm not sure.

> So suddenly you are on my side? I don't even get what are you arguing
> about at this point.

By this time, I forgot, too :).

> --
>                       Gleb.