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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2012-04-23 at 17:25 +0100, Roger Pau Monne wrote:
> Ian Campbell escribiÃ:
> > 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?
> 
> For vbd devices we write it everytime, for vifs devices we write it if 
> disable_xl_vif_scripts is not set.
> 
> > Or is it necessary to use the override config option for
> > driver domain?
> 
> So the new proposal is to add a disable_xl_vbd_scripts and to detect if 
> the device backend is different than dom0, if it is in fact different 
> than dom0 don't execute hotplug scripts from xl (this will only work for 
> vifs, because there's no support for setting the device domain for vbd 
> devices yet).

If we can detect I don't see why we shouldn't, unless it turns out to
add complexity which we want to defer until 4.3.

Ian.



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