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SubjectRe: Going beyond 256 PCI buses

Jeff Garzik writes:
> Why do you want to make the bus number larger than the PCI bus number
> register?

This isn't it. What I'm trying to provoke thought on is
"is there a way to make mindless apps using these syscalls
work transparently"

I think the answer is no. Apps should really fetch info out
of /proc/bus/pci and use the controller ioctl.

But someone could surprise me :-)

> It seems like adding 'unsigned int domain_num' makes more sense, and is
> more correct. Maybe that implies fixing up other code to use a
> (domain,bus) pair, but that's IMHO a much better change than totally
> changing the interpretation of pci_bus::bus_number...

Correct, I agree. But I don't even believe we should be sticking
the domain thing into struct pci_bus.

It's a platform thing. Most platforms have a single domain, so why
clutter up struct pci_bus with this value? By this reasoning we could
say that since it's arch-specific, this stuff belongs in sysdata or
wherever.

And this is what is happening right now. So in essence, the work is
done :-) The only "limiting factor" is that x86 doesn't support
multiple domains as some other platforms do. So all these hot-plug
patches just need to use domains properly, and perhaps add domain
support to X86 when one of these hot-plug capable controllers are
being used.

> > 2) Figure out what to do wrt. sys_pciconfig_{read,write}()
>
> 3) (tiny issue) Change pci_dev::slot_name such that it includes the
> domain number. This is passed to userspace by SCSI and net drivers as a
> way to allow userspace to associate a kernel interface with a bus
> device.

Sure. It's an address and the domain is part of the address.

Later,
David S. Miller
davem@redhat.com

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