linux-kernel - Re: [PATCH] drm: drm_gem.h: Add explicit includes for DEFINE_DRM_GEM

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Date:   Wed, 4 May 2022 11:38:51 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     Jeffrey Hugo <quic_jhugo@...cinc.com>,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, airlied@...ux.ie, daniel@...ll.ch,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm: drm_gem.h: Add explicit includes for
 DEFINE_DRM_GEM_FOPS

On Mon, May 02, 2022 at 06:41:39PM +0300, Jani Nikula wrote:
> On Fri, 29 Apr 2022, Jeffrey Hugo <quic_jhugo@...cinc.com> wrote:
> > DEFINE_DRM_GEM_FOPS() references drm functions from other headers.  For
> > example drm_open() is defined in drm_file.h and drm_ioctl() is defined
> > in drm_ioctl.h.  Since drm_gem.h doesn't include these headers, it
> > relies on an implicit include from the .c file to have included these
> > required headers before DEFINE_DRM_GEM_FOPS() gets used.  Relying on
> > these implicit includes can cause build failures for new code that
> > doesn't know about these requirements, and can lead to future problems
> > if the headers ever get restructured as there will be a need to update
> > every downstream file that includes drm_gem.h.
> >
> > Lets fix this explicitly including the required headers in drm_gem.h so
> > that code that includes drm_gem.h does not need to worry about these
> > implicit dependencies.
> 
> In the general case, I tend to agree, but in this specific instance I
> think I'd err on the side of fewer includes. I think the more likely
> outcome here is accumulating implicit dependencies on symbols from
> drm_file.h and drm_ioctl.h by including drm_gem.h only!
> 
> I do think headers need to be self-contained, and we actually enforce
> this in i915 (see HDRTEST in drivers/gpu/drm/i915/Makefile), but not to
> the point of macro expansions.

Yeah we abuse macros in a bunch of places to untangle header dependencies,
so then going back and pulling in all the headers back in feels a bit
silly and defeats the point.

iow, I concur.
-Daniel

> 
> BR,
> Jani.
> 
> 
> 
> >
> > Signed-off-by: Jeffrey Hugo <quic_jhugo@...cinc.com>
> > ---
> >  include/drm/drm_gem.h | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> > index 9d7c61a..1cbe3d8 100644
> > --- a/include/drm/drm_gem.h
> > +++ b/include/drm/drm_gem.h
> > @@ -37,6 +37,8 @@
> >  #include <linux/kref.h>
> >  #include <linux/dma-resv.h>
> >  
> > +#include <drm/drm_file.h>
> > +#include <drm/drm_ioctl.h>
> >  #include <drm/drm_vma_manager.h>
> >  
> >  struct iosys_map;
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch