The controlD device

Thomas Hellstrom thellstrom at
Fri Oct 21 09:03:27 PDT 2011

On 10/21/2011 04:36 PM, Dave Airlie wrote:
> On Fri, Oct 21, 2011 at 3:18 PM, Dave Airlie<airlied at>  wrote:
>> On Fri, Oct 21, 2011 at 3:06 PM, Thomas Hellstrom<thellstrom at>  wrote:
>>> Dave,
>>> What is the drm control device nodes really used for?
>>> On my fc14 system it seems like it has world rw privileges, and full access
>>> to all modesetting ioctls.
>>> Is that the intention?
>> No, and I just realised we packaged a broken udev rule.
>> It should be root only, oops.
>> Its intention is for setting up multi-seat and gpgpu access to the drm.
>> change /etc/udev/rules.d/91-modeset.rules to be 0600.
> I've filed updates to Fedora to fix this, no other distro should be
> using or caring about these device nodes yet, since we never really
> got GPGPU going yet.
> Dave.
Sounds good. I was actually mostly curios on the intended usage pattern 
of the control node.
I found some things on the DRM wikis, but it doesn't at all seem 
consistent with what's in DRM.

Why do we have CONTROL_ALLOW on all modesetting ioctls?, also this code 
in drm_crtc.c  seems odd:

if (file_priv->master->minor->type == DRM_MINOR_CONTROL) {

Isn't that equivalent to

if (file_priv->minor->type == DRM_MINOR_CONTROL) { ?

Any enlightenment would be appreciated.


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