Re: [PATCH 01/22] drm: Add drm_mode_init()

[Andrzej Hajda <andrzej.hajda@intel.com>]

On 18.02.2022 11:03, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Add a variant of drm_mode_copy() that explicitly clears out
> the list head of the destination mode. Helpful to guarantee
> we don't have stack garbage left in there for on-stack modes.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>   drivers/gpu/drm/drm_modes.c | 17 +++++++++++++++++
>   include/drm/drm_modes.h     |  2 ++
>   2 files changed, 19 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index 96b13e36293c..40d4ce4a1da4 100644
> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -892,6 +892,23 @@ void drm_mode_copy(struct drm_display_mode *dst, const struct drm_display_mode *
>   }
>   EXPORT_SYMBOL(drm_mode_copy);
>   
> +/**
> + * drm_mode_init - initialize the mode from another mode
> + * @dst: mode to overwrite
> + * @src: mode to copy
> + *
> + * Copy an existing mode into another mode, zeroing the
> + * list head of the destination mode. Typically used
> + * to guarantee the list head is not left with stack
> + * garbage in on-stack modes.
> + */
> +void drm_mode_init(struct drm_display_mode *dst, const struct drm_display_mode *src)
> +{
> +	memset(dst, 0, sizeof(*dst));

Why not just clear the list head? Or maybe poison it? It would be more 
cleaner.

I wonder why there is no such helper in list.h.


Regards
Andrzej

> +	drm_mode_copy(dst, src);
> +}
> +EXPORT_SYMBOL(drm_mode_init);
> +
>   /**
>    * drm_mode_duplicate - allocate and duplicate an existing mode
>    * @dev: drm_device to allocate the duplicated mode for
> diff --git a/include/drm/drm_modes.h b/include/drm/drm_modes.h
> index 29ba4adf0c53..e6e5a588fab1 100644
> --- a/include/drm/drm_modes.h
> +++ b/include/drm/drm_modes.h
> @@ -484,6 +484,8 @@ void drm_mode_set_crtcinfo(struct drm_display_mode *p,
>   			   int adjust_flags);
>   void drm_mode_copy(struct drm_display_mode *dst,
>   		   const struct drm_display_mode *src);
> +void drm_mode_init(struct drm_display_mode *dst,
> +		   const struct drm_display_mode *src);
>   struct drm_display_mode *drm_mode_duplicate(struct drm_device *dev,
>   					    const struct drm_display_mode *mode);
>   bool drm_mode_match(const struct drm_display_mode *mode1,