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

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Date:   Mon, 02 May 2022 18:41:39 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Jeffrey Hugo <quic_jhugo@...cinc.com>,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, airlied@...ux.ie, daniel@...ll.ch
Cc:     Jeffrey Hugo <quic_jhugo@...cinc.com>,
        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 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.

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