[libvirt] Analysis of the effect of adding PCIe root ports

[Andrea Bolognani]

On Wed, 2016-10-05 at 18:36 +0100, Richard W.M. Jones wrote:
> > > (b) It would be nice to turn the whole thing off for people who don't
> > > care about / need hotplugging.
> > 
> > I had contemplated having an "availablePCIeSlots" (or something like
> > that) that was either an attribute of the config, or an option in
> > qemu.conf or libvirtd.conf. If we had such a setting, it could be
> > set to "0".

I remember some pushback when this was proposed. Maybe we
should just give up on the idea of providing spare
hotpluggable PCIe slots by default and ask the user to add
them explicitly after all.

> Note that changes to libvirt conf files are not usable by libguestfs.
> 
> The setting would need to go into the XML, and please also make it
> possible to determine if $random version of libvirt supports the
> setting, either by a version check or something in capabilities.

Note that you can avoid using any PCIe root port at all by
assigning PCI addresses manually. It looks like the overhead
for the small (I'm assuming) number of devices a libguestfs
appliance will use is low enough that you will probably not
want to open that can of worm, though.

-- 
Andrea Bolognani / Red Hat / Virtualization