Re: [Qemu-devel] [Qemu-ppc] [PATCH 12/12] pseries: Generate unique LIOBNs for PCI host bridges

[Alexander Graf]

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 <address@hidden>
>>> 
>>> 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 <address@hidden>
>>> Signed-off-by: David Gibson <address@hidden>
>> 
>> 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?


Alex