Re: [libvirt] [PATCH v4 4/4] auto-create pci-bridge controller info

On Mon, Mar 04, 2013 at 02:39:40PM -0500, Laine Stump wrote: > On 03/04/2013 11:51 AM, Ján Tomko wrote: >> It would be nice if we could add pci bridges even when there weren't any >> specified in the XML, but there are too many PCI devices. I don't know >> what would be the nicest way to do that. > > If we auto-assign addresses for un-addressed devices first (your recent > patches did that, right? I forget the status of those), *then* > auto-create the required bridges (which themselves will need an > auto-assigned address), that should just happen. > > Of course, if we do that, then we won't have reserved any slots on bus 0 > for even a single pci-bridge device, so we'll fail. Is the proper way > out of this to always reserve one (or maybe two, for good measure) slots > on any given bus to be used only for bridges? That way no matter how out > of hand things get, we'll always have a place we can add another bus. > (In the case of *lots* of devices, I assume that a device on a nested > PCI bridge would be less efficient, and may have some other limitations, > but it would be better than nothing. And if the admin was really > concerned about that, they could modify their config to explicitly place > several bridges directly on bus 0)

You'd have todo a 2 pass assignment. First count the number of devices that need to have PCI addresses assigned. Then create the required number of bridges, then assign the addresses.