DRM_CONTROL node breakage (Re: [PATCH] [RFC] drm: Nerf DRM_CONTROL nodes)

From: Thomas Hellstrom
Date: Tue Feb 21 2017 - 00:33:34 EST


IMO Not fixing this immediately through stable is out of the question.
The deal is that we don't break userspace.
Having said that, I'm not against a long term vmwgfx-only solution. But
let's fix this now.

Admittedly we missed testing this but you got to understand that not all
developer teams have a multitude of
developers (we have on average one for the whole linux graphics driver
stack except GL), and the bug
doesn't show up for QE on regression testing unless they run
gnome-sheel/Wayland which they currently don't, and I guess they've been
focused on the fb2 regression.

It's no secret that we've been using the control nodes for some time.
The CONTROL_ALLOW is present in the
driver private ioctls and the commit has been there since 2016.

The user-space code has been present in vmware-tools also since that
commit and due to the long release cycles of
open-vm-tools the open-vm-tools version was just about to be released.
It's necessary for non-xorg


On 02/20/2017 11:22 PM, Daniel Vetter wrote:
> On Sun, Feb 19, 2017 at 4:21 PM, Thomas Hellstrom <thomas@xxxxxxxxxxxx> wrote:
>> So I think we need a quick revert of this commit or a quick stable
>> follow-up to unbreak things on our side.
> I'd much prefer we just register control nodes for vmwgfx only, with a
> commit message explaining in detail what exactly your control tool is
> using (i.e. which ioctl), plus links to the source code for future
> references. Also not sold on the immediate revert, this stuff has been
> merged since months.
> -Daniel
>> /Thomas
>> On 02/19/2017 03:54 PM, Thomas Hellstrom wrote:
>>> Hi!
>>> This patch breaks the vmwgfx resolutionKMS daemon which opens a control
>>> node to tell DRM about the monitor layout...
>>> /Thomas
>>> On 10/28/2016 10:10 AM, Daniel Vetter wrote:
>>>> Looking at the ioctl permission checks I noticed that it's impossible
>>>> to import gem buffers into a control nodes, and fd2handle/handle2fd
>>>> also don't work, so no joy with dma-bufs.
>>>> The only way to do anything with a control node is by drawing stuff
>>>> into a dumb buffer and displaying that. I suspect control nodes are an
>>>> entirely unused thing, and a cursory check shows that there does not
>>>> seem to be any callers of drmOpenControl nor of the other drmOpen
>>>> functions using DRM_MODE_CONTROL.
>>>> Since I don't like dead uabi, let's remove it. But since this would be
>>>> a really big change I think it's better to start out small by simply
>>>> not registering anything. We can garbage-collect the dead code later
>>>> on, once we're sure it's really not used anywhere.
>>>> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
>>>> ---
>>>> drivers/gpu/drm/drm_drv.c | 6 ------
>>>> 1 file changed, 6 deletions(-)
>>>> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
>>>> index 6efdba4993fc..f085e28ffc6f 100644
>>>> --- a/drivers/gpu/drm/drm_drv.c
>>>> +++ b/drivers/gpu/drm/drm_drv.c
>>>> @@ -517,12 +517,6 @@ int drm_dev_init(struct drm_device *dev,
>>>> goto err_free;
>>>> }
>>>> - if (drm_core_check_feature(dev, DRIVER_MODESET)) {
>>>> - ret = drm_minor_alloc(dev, DRM_MINOR_CONTROL);
>>>> - if (ret)
>>>> - goto err_minors;
>>>> - }
>>>> -
>>>> if (drm_core_check_feature(dev, DRIVER_RENDER)) {
>>>> ret = drm_minor_alloc(dev, DRM_MINOR_RENDER);
>>>> if (ret)
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