Xen devel - Aug 2005 - RE: SPAM: Re: AW: PCI bus emulation?

>> It shuld be possible for domain 0 to read all devices from the bus and
>> build its list. Then domain 0 could take the to-be-hidden devices out
of
>> that list
>
>Yep.  Do you think it''s possible to simply chop these devices out
of the
>list 
>after initialisation but before passing up to the generic PCI layer?
>That''d 
>be excellent.

That''d be OS-specific, no?
I mean, do we know that all kernels in this world have a clean ability to
Support this? Despite that this is probably not what the kernel developers
expected, thus their pci-codes may look strange after adding such feature,
I think.
(totally unsure because I actually never wrote kernel code yet ;))

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> >Yep.  Do you think it''s possible to simply chop these devices
out of the
> >list
> >after initialisation but before passing up to the generic PCI layer?
> >That''d
> >be excellent.
>
> That''d be OS-specific, no?
Yep.  With the new PCI architecture with dom0 owning the PCI bus, this stuff 
is going to need implementing in each dom0 OS.  The same goes for any dom0 
code but since 3.0 pushes more stuff up to dom0, there''ll be more stuff
to
worry about.

It''s a tradeoff, though: in return for this, we get better hardware
support,
reduce code duplication and make Xen''s codebase smaller.
> I mean, do we know that all kernels in this world have a clean ability to
> Support this? Despite that this is probably not what the kernel developers
> expected, thus their pci-codes may look strange after adding such feature,
> I think.
> (totally unsure because I actually never wrote kernel code yet ;))
No, it''s a good point.  It may be that some kernels will be better or
worse
suited to this.  However, for a portable OS it''s probably possible to
do some
tricks in the arch/ subdir.  If any other code gets confused by this, it may 
need fixing, however it''s only the core PCI code that''ll be
affected rather
than all PCI drivers - it should be possible to audit the interface to check 
it won''t break.

As an alternative, if the ability to ignore certain PCI devices is useful 
outside Xen (e.g. for excluding faulty devices), it could be added to the 
core PCI code, then all systems would benefit from it.

Cheers,
Mark

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