Re: [Xen-devel] [PATCH 4 of 5] libxl: Add support for passing in the machine's E820 for PCI passthrough

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Fri, 2011-04-08 at 15:09 +0100, Tim Deegan wrote:
> At 14:55 +0100 on 08 Apr (1302274509), Ian Campbell wrote:
> > On Fri, 2011-04-08 at 14:35 +0100, Konrad Rzeszutek Wilk wrote:
> > > On Fri, Apr 08, 2011 at 11:56:52AM +0100, Ian Jackson wrote:
> > > > Ian Campbell writes ("Re: [Xen-devel] [PATCH 4 of 5] libxl: Add support 
> > > > for passing in the machine's E820 for PCI passthrough"):
> > > > > Are we expecting that libxl users might want to modify the e820? If 
> > > > > not
> > > > > then why expose libxl_e820_alloc and libxl_e820_sanitize at all, just
> > > > > add a flag to the libxl interface which says whether or not to 
> > > > > provide a
> > > > > host-derived e820.
> > > > 
> > > > Well, also, why do we need that flag at all ?  Are we trying to do
> > > > something different with domains which might get pci passthrough ?  If
> > > 
> > > Yes. Well, it does work OK even if you are _not_ doing PCI passthrough.
> > > But the main users for this are the ones doing PCI passthrough.
> > > 
> > > > so then that's what should be specified at the libxl api, surely,
> > > > rather than some opaque "write this rune to make it work" option.
> > > 
> > > OK. If I am understanding you guys right, you are saying, latch
> > > it of the 'pci' option instead of this 'pci_hole' option.
> > 
> > ACK. For the pure-hotplug case an empty pci=[] ought to suffice to
> > trigger this functionality.
> 
> That's a _horrible_ config syntax.

fair enough. I thought it nicely represented the "has an empty PCI bus"
myself...
 
>   We should either do this for all
> guests or give it its own option (which can default to 1 for guests with
> non-empty passthrough lists if you like). 

Ack, if it's an option it should definitely default to on for non-empty
pci passthrough lists. I think we can probably get away with default on
always though and allow it to be explicitly disabled. That's really just
a case of trying on a few PV OSes and seeing how much they barf...

Ian.



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