[libvirt] need custom /dev entries in LXC

[Daniel P. Berrange]

On Wed, May 22, 2013 at 06:22:12PM -0400, Michael R. Hines wrote:
> Hi,
> 
> We run nvidia devices inside libvirt-managed LXC containers.
> 
> It used to be that simply doing:
> 
> $ echo 'c 195:* rwm' > /sys/fs/cgroup/devices/libvirt/lxc
> 
> Then, after booting the container, we would do:
> 
> $ mknod -m 666 /dev/nvidia0 c 195 0
> 
> .... would be good enough to run our CUDA applications.
> 
> But, according to:
> 
> $ cat src/lxc/lxc_container.c
> 
> The CAP_MKNOD capability is being dropped and only a specific
> set of devices is being created before booting the container.
> 
> Is there any reason why this is not per-device configurable?

With recent libvirt you can pass through arbitrary block and
character devices explicitly, using the following XML:

  http://libvirt.org/formatdomain.html#elementsHostDevCaps

As such there is never any need to change cgroups or use
mknod as you describe.


Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|