[PATCH 4/5] drm/vmwgfx: remove custom ioctl io encoding check

[Emil Velikov]

On 2019/05/24, Thomas Hellstrom wrote:
> On Fri, 2019-05-24 at 13:14 +0100, Emil Velikov wrote:
> > On 2019/05/23, Thomas Hellstrom wrote:
> > > Hi, Emil,
> > > 
> > > On Wed, 2019-05-22 at 17:41 +0100, Emil Velikov wrote:
> > > > From: Emil Velikov <emil.velikov at collabora.com>
> > > > 
> > > > Drop the custom ioctl io encoding check - core drm does it for
> > > > us.
> > > 
> > > I fail to see where the core does this, or do I miss something?
> > 
> > drm_ioctl() allows for the encoding to be changed and attributes that
> > only the
> > appropriate size is copied in/out of the kernel.
> > 
> > Technically the function is more relaxed relative to the vmwgfx
> > check, yet
> > seems perfectly reasonable.
> > 
> > Is there any corner-case that isn't but should be handled in
> > drm_ioctl()?
> 
> I'd like to turn the question around and ask whether there's a reason
> we should relax the vmwgfx test? In the past it has trapped quite a few
> user-space errors.
> 
The way I see it either:
 - the check, as-is, is unnessesary, or
 - it is needed, and we should do something equivalent for all of DRM

We had a very long brainstorming session with a colleague and we could not see
any cases where this would cause a problem. If you recall anything concrete
please let me know - I would be more than happy to take a closer look.

Thanks
Emil