Re: [PATCH 08/10] drm: Forbid legacy MAP functions for DRIVER_MODESET

From: Daniel Vetter <daniel@ffwll.ch>
To: Emil Velikov <emil.l.velikov@gmail.com>
Cc: Peter Antoine <peter.antoine@intel.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Ben Skeggs <bskeggs@redhat.com>,
	Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 08/10] drm: Forbid legacy MAP functions for DRIVER_MODESET
Date: Thu, 14 Apr 2016 12:06:03 +0200	[thread overview]
Message-ID: <20160414100603.GL2510@phenom.ffwll.local> (raw)
In-Reply-To: <CACvgo51TM18dONKfWL3wDH98D9GooMjzkyHsLq8pw0v6nRWdAQ@mail.gmail.com>

On Wed, Mar 30, 2016 at 11:39:01AM +0100, Emil Velikov wrote:
> On 30 March 2016 at 10:45, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> > Like in
> >
> > commit 0e975980d435d58df2d430d688b8c18778b42218
> > Author: Peter Antoine <peter.antoine@intel.com>
> > Date:   Tue Jun 23 08:18:49 2015 +0100
> >
> >     drm: Turn off Legacy Context Functions
> >
> > we need to again make an exception for nouveau, but everyone else
> > really doesn't need this.
> >
> > Cc: Peter Antoine <peter.antoine@intel.com>
> > Cc: Ben Skeggs <bskeggs@redhat.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > ---
> >  drivers/gpu/drm/drm_bufs.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_bufs.c b/drivers/gpu/drm/drm_bufs.c
> > index d92db7007f62..e8a12a4fd400 100644
> > --- a/drivers/gpu/drm/drm_bufs.c
> > +++ b/drivers/gpu/drm/drm_bufs.c
> > @@ -396,6 +396,10 @@ int drm_legacy_addmap_ioctl(struct drm_device *dev, void *data,
> >         if (!(capable(CAP_SYS_ADMIN) || map->type == _DRM_AGP || map->type == _DRM_SHM))
> >                 return -EPERM;
> >
> > +       if (!drm_core_check_feature(dev, DRIVER_KMS_LEGACY_CONTEXT) &&
> > +           drm_core_check_feature(dev, DRIVER_MODESET))
> > +               return -EINVAL;
> > +
> Wondering if making this the first check in the function won't be
> better ? We have a handful of places which preemptively check
> DRIVER_MODESET prior to calling drm_legacy functions and similarly
> some (last time I've looked) drm_legacy functions check for
> DRIVER_MODESET. Perhaps we can move all the checking into the
> drm_legacy API alone ?

This is an ioctl handler, so there's not really any caller we can move
this to. In general I'm split, and I just put checks like these wherever
it makes sense, pulling them out into callers if there's an entire pile of
them who all want the same checks.

In the end I don't think it matters, as long as we dutifully combine
drm_legacy_* with such checks, so that it's _really_ all dead code for
modern drives.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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