Re: [Xen-devel] [PATCH] dom0 linux: support SBDF with "guestdev=" andremove "reassigndev="

[Yuji Shimada <shimada-yxb@xxxxxxxxxxxxxxx>]

On Thu, 09 Apr 2009 11:39:45 +0100
"Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> >>> Yuji Shimada <shimada-yxb@xxxxxxxxxxxxxxx> 08.04.09 10:30 >>>
> >This patch supports SBDF with "guestdev=" boot parameter and removes
> >"reassigndev=" boot parameter.
> >
> >Currently there are three boot parameters which specifics PCI device
> >for PCI pass-through.
> >
> >        pciback.hide=
> >        guestdev=
> >        reassigndev=
> >
> >I'd like to simplify them before xen 3.4 is released. To achieve this,
> >I'd like to make "guestdev=" boot parameter support SBDF, and remove
> >"reassigndev=".
> >
> >
> >When we don't need to reassign resources and use device path,
> >pciback.hide= boot parameter can be used. The parameter is also needed
> >for backward compatibility.
> >
> >    pciback.hide=(00:01.0)(00:02.0)
> >
> >When we need to reassign resources or use device path, guestdev= boot
> >parameter can be used. reassign_resources boot parameter is needed to
> >reassign resources, too.
> >
> >    guestdev=00:01.0,00:02.0 reassign_resources
> >    guestdev=PNP0A08:0-1.0,PNP0A08:0-2.0
> >    guestdev=PNP0A08:0-1.0,PNP0A08:0-2.0 reassign_resources
> 
> Which basically means reassignment of resources will become and all-or-
> nothing feature rather than a per-device one - is that really intended? It
> seems like a step backwards to me.

Reassignment of resources is all-or-nothing feature.
When reassign_resources is specified, all PCI devices specified by
"guestdev=" are the targets of reassignment. Please note that PCI
devices which are not specified by "guestdev=" are not the targets of
reassignment.

To avoid fragmentation of resources, all-or-nothing is better than
per-device. On the other hand, if there is a device which cause some
issues on reassignment, per-device is needed. But I have not seen such
a device yet.

Thanks,
--
Yuji Shimada


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