Re: [Xen-devel] [PATCH, RFC 0/7] PCI multi-segment support

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.09.11 at 16:05, Keir Fraser <keir@xxxxxxx> wrote:
> On 05/09/2011 14:49, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> 
>>>>> On 05.09.11 at 15:33, Keir Fraser <keir.xen@xxxxxxxxx> wrote:
>>> On 05/09/2011 14:18, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>>> 
>>>>>>> On 25.08.11 at 16:54, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>>>>> In order for Xen to be able to boot on systems with multiple PCI segments
>>>>> (also called domains), a number of changes are necessary to the
>>>>> hypervisor, the hypercall interface, the tools, and the Dom0 kernel, as
>>>>> in most code paths and definitions there were not even provisions for
>>>>> passing a segment number.
>>>>> 
>>>>> The hypercall interface changes may need some discussion before
>>>>> applying the patches, in particular
>>>>> 
>>>>> - whether the way PHYSDEVOP_map_pirq gets re-used is acceptable,
>>>>>   or whether alternatively we should define a replacement one sub-
>>>>>   hypercall
>>>>> - whether PHYSDEVOP_manage_pci_* should be deprecated
>>>>> - whether the bit assignments for the four uses of machine_bdf in
>>>>>   the domctl interface can be re-defined
>>>> 
>>>> No comment from either of you on the proposed changes?
>>> 
>>> I'm personally fine with folding segment into the bus field. Otherwise we
>>> just end up with more compat cruft.
>>> 
>>> I don't have an opinion on the PHYSDEVOP_manage_pci_* hypercalls. In fact I
>>> don't know much about them at all.
>>> 
>>> I've always considered the domctl interface subject to change, but you don't
>>> seem to redefine anything that already exists? You just give meaning to bits
>>> 24-31 of an existing 32-bit parameter?
>> 
>> I'm trying to avoid incompatible changes when possible (due to
>> out-of-tree consumers like libvirt,
> 
> I think the intention is to maintain API compatibility for libxenlight, and
> have out-of-tree tool stacks/librariues build on top of that.
> 
> I think there are libvirt bindings to libxenlight now, for example?
> 
> My conclusion would be you can do the cleaner change to domctl. Interested
> in Ian Jackson's view however.

Ian?

>> and due to the hacks required to
>> use domctl interfaces from the kernel). Now here we need 16 bits, but
>> have two sets of 8 (at bottom and top), hence I'd favor doing an
>> incompatible change here (moving the bdf bits down to 0...15, and
>> using 16...31 for the segment), perhaps renaming the field to
>> machine_sbdf (to force compile-time noticing of the change at least
>> for those that actually use our headers). But as the odd bit assignment
>> could have other (hidden) reasons I coded things first to not do any
>> re-assignments.
>> 
>> Jan
>> 




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