Re: [Xen-devel] [PATCH] Add missing modprobe to xencommons

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2011-11-24 at 18:31 +0000, Ian Jackson wrote:
> Paul Durrant writes ("[Xen-devel] [PATCH] Add missing modprobe to 
> xencommons"):
> > Add missing modprobe to xencommons
> ...
> > +           modprobe xen-evtchn
> 
> Is this really the way we want to do things ?  I guess it's a
> plausible thing to do which is harmless if the module name doesn't
> change.

I thought we already did this sort of thing somewhere (I thought it was
xencommons) but I guess not.

> But perhaps something else in the system should be organising that
> evtchn gets loaded ?

The problem is, I think, that there is no actual device which would
trigger the Linux hotplug subsystem to try and load this module. There
is a similar problem with things like /dev/loop. This has been a problem
since udev removed (or at least obfuscated) the old behaviour of having
a /dev node with no backing driver and modprobing on open.

Debian has /etc/udev/links.conf which says:
# This file does not exist. Please do not ask the Debian maintainer about it.
# If you need manually created devices, create them in /lib/udev/devices/ .

/lib/udev/devices is empty on my system and I can't see any
documentation about what one should create there (actual dev nodes?) In
any case it appears to be Debian specific.

We could perhaps cause the xenbus code or some other suitably core thing
to generate a hotplug event to cause these things to be autoloaded?

Also this is the sort of thing which (lib)xl could and should trivially
sanity check for at start of day.

>   Also, this isn't the only module we need.
> 
> Ian.
> 
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