Re: [Xen-devel] [PATCH v3 0/5] libxl: call hotplug scripts from libxl

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2012-04-23 at 14:31 +0100, Roger Pau Monne wrote:
> Marek Marczykowski escribiÃ:
> > On 20.04.2012 15:23, Roger Pau Monne wrote:
> >> This series removes the use of udev rules to call hotplug scripts when 
> >> using
> >> libxl. Scripts are directly called from the toolstack at the necessary 
> >> points,
> >> making use of the new event library and it's fork support.
> >
> > What about non-dom0 backends? There will be no simple way to execute script
> > there by libxl without help from udev...
> 
> A new config option has been added on this series 
> (disable_xl_vif_scripts) that allows the user to keep executing vif 
> scripts from udev, so this functionality is not lost.

In the long term (e.g. for 4.3) we intend to overhaul this in a way
which makes driver domains work without udev at all, see "Driver domains
communication protocol proposal" posted by Ian Jackson several weeks ago
-- it would be good to confirm that the scheme proposed there works well
for Qubes-OS too.

In the short term (i.e. 4.2) we felt it was too late to be making these
sorts of changes (e.g. implementing that complete protocol) and
therefore the compromise is that xl will execute the scripts only in the
case that dom0 is also the backend domain while for driver domains we
retain the pre-4.2 behaviour of executing the hotplug scripts via udev
inside the driver domain. This was necessary in order to fix things such
as teardown of disks on NetBSD and teardown of NICs on openvswitch
(currently both are broken even with backend = dom0 due to short comings
in the previous approach) while not regressing the driver domain use
case.

By default do we write the xenstore key to suppress udev running the
scripts regardless of which domain the backend is in or only for
backend=0? Or is it necessary to use the override config option for
driver domain?

Ian.

> > In Qubes-OS we heavily use network backend in domU: dom0 have no network at
> > all, all NICs are attached (as PCI device) to some domU - called NetVM, 
> > where
> > network backend resides.
> 
> There should be no problem with that, you will just need to use the new 
> option.
> 
> > Also vbd backend in domU is used - eg to boot HVM from iso, which is stored 
> > in
> > some domU.
> 
> I didn't know you where able to use vbd from driver domains with xl, if 
> so I will have to add a similar option for vbd devices 
> (disable_xl_vbd_scripts).
> 
> 
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