On Wed, Nov 21, 2012 at 11:09:50AM +0100, Alexander Graf wrote: > > > On 21.11.2012, at 06:00, David Gibson <[email protected]> wrote: > > > On Tue, Nov 20, 2012 at 10:27:11AM +0100, Alexander Graf wrote: > >> > >> On 19.11.2012, at 23:51, David Gibson wrote: > >> > >>> On Mon, Nov 19, 2012 at 05:34:12PM +0100, Alexander Graf wrote: > >>>> > >>>> On 13.11.2012, at 03:47, David Gibson wrote: > >>>> > >>>>> From: Alexey Kardashevskiy <[email protected]> > >>>>> > >>>>> In future (with VFIO) we will have multiple PCI host bridges on > >>>>> pseries. Each one needs a unique LIOBN (IOMMU id). At the moment we > >>>>> derive these from the pci domain number, but the whole notion of > >>>>> domain numbers on the qemu side is bogus and in any case they're not > >>>>> actually uniquely allocated at this point. > >>>>> > >>>>> This patch, therefore uses a simple sequence counter to generate > >>>>> unique LIOBNs for PCI host bridges. > >>>>> > >>>>> Signed-off-by: Alexey Kardashevskiy <[email protected]> > >>>>> Signed-off-by: David Gibson <[email protected]> > >>>> > >>>> I don't really like the idea of having a global variable just > >>>> because our domain ID generation seems to not work as > >>>> expected. Michael, any comments here? > >>> > >>> Well, the patch I sent which changed domain id generation was > >>> ignored. In any case, as I said, the whole concept of domain numbers > >> > >> Michael? > >> > >>> makes no sense on the qemu side, so I don't think increasing reliance > >>> on them by using them here is a good idea. > >>> > >>> It would be conceptually nicer to derive the liobn from the buid, but > >>> that would rely on the buid's being unique in the low 32-bits, which > >>> is true in practice, but seems risky to rely on. > >> > >> Well, there has to be some uniqueness from the guest's POV already, > >> no? > > > > Yes, the BUIDs are unique, but they are 64-bit, whereas the LIOBN is > > only 32-bit. > > Tricky. Michael, any ideas? > > Alex
Whatever scheme we come up with, becomes part of guest ABI that we have to maintain. So rather than maintain it, I think it's easiest to require full specification from users, and verify uniqueness. > > > > -- > > 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
