Re: [PATCH RESEND v2 05/32] drm/vkms: Introduce config for plane name

["José Expósito" <jose.exposito89@gmail.com>]

On Wed, Oct 29, 2025 at 03:36:42PM +0100, Louis Chauvet wrote:
> As planes can have a name in DRM, prepare VKMS to configure it using
> ConfigFS.
> 
> Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
> ---
>  drivers/gpu/drm/vkms/vkms_config.c |  4 ++++
>  drivers/gpu/drm/vkms/vkms_config.h | 26 ++++++++++++++++++++++++++
>  drivers/gpu/drm/vkms/vkms_drv.h    |  5 +++--
>  drivers/gpu/drm/vkms/vkms_output.c |  6 +-----
>  drivers/gpu/drm/vkms/vkms_plane.c  |  6 ++++--
>  5 files changed, 38 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_config.c b/drivers/gpu/drm/vkms/vkms_config.c
> index 858bec2d1312..bfafb5d2504d 100644
> --- a/drivers/gpu/drm/vkms/vkms_config.c
> +++ b/drivers/gpu/drm/vkms/vkms_config.c
> @@ -352,6 +352,8 @@ static int vkms_config_show(struct seq_file *m, void *data)
>  		seq_puts(m, "plane:\n");
>  		seq_printf(m, "\ttype=%s\n",
>  			   drm_get_plane_type_name(vkms_config_plane_get_type(plane_cfg)));
> +		seq_printf(m, "\tname=%s\n",
> +			   vkms_config_plane_get_name(plane_cfg));

I discovered this while working on some basic IGT tests to validate
your changes.

I think that this triggers undefined behavior. printf() and friends
expect a non NULL value for %s:
https://stackoverflow.com/a/11589479

In my Fedora system, this prints "name=(null)", instead of an empty
string.

The same happens with the ConfigFS API:

$ cat /sys/kernel/config/vkms/test_plane_default_values/planes/plane0/name
(null)

We'd need to return in both places an empty string instead.

>  	}
>  
>  	vkms_config_for_each_crtc(vkmsdev->config, crtc_cfg) {
> @@ -392,6 +394,7 @@ struct vkms_config_plane *vkms_config_create_plane(struct vkms_config *config)
>  
>  	plane_cfg->config = config;
>  	vkms_config_plane_set_type(plane_cfg, DRM_PLANE_TYPE_OVERLAY);
> +	vkms_config_plane_set_name(plane_cfg, NULL);
>  	xa_init_flags(&plane_cfg->possible_crtcs, XA_FLAGS_ALLOC);
>  
>  	list_add_tail(&plane_cfg->link, &config->planes);
> @@ -404,6 +407,7 @@ void vkms_config_destroy_plane(struct vkms_config_plane *plane_cfg)
>  {
>  	xa_destroy(&plane_cfg->possible_crtcs);
>  	list_del(&plane_cfg->link);
> +	kfree_const(plane_cfg->name);
>  	kfree(plane_cfg);
>  }
>  EXPORT_SYMBOL_IF_KUNIT(vkms_config_destroy_plane);
> diff --git a/drivers/gpu/drm/vkms/vkms_config.h b/drivers/gpu/drm/vkms/vkms_config.h
> index 4c8d668e7ef8..57342db5795a 100644
> --- a/drivers/gpu/drm/vkms/vkms_config.h
> +++ b/drivers/gpu/drm/vkms/vkms_config.h
> @@ -35,6 +35,7 @@ struct vkms_config {
>   *
>   * @link: Link to the others planes in vkms_config
>   * @config: The vkms_config this plane belongs to
> + * @name: Name of the plane
>   * @type: Type of the plane. The creator of configuration needs to ensures that
>   *        at least one primary plane is present.
>   * @possible_crtcs: Array of CRTCs that can be used with this plane
> @@ -47,6 +48,7 @@ struct vkms_config_plane {
>  	struct list_head link;
>  	struct vkms_config *config;
>  
> +	const char *name;
>  	enum drm_plane_type type;
>  	struct xarray possible_crtcs;
>  
> @@ -288,6 +290,30 @@ vkms_config_plane_set_type(struct vkms_config_plane *plane_cfg,
>  	plane_cfg->type = type;
>  }
>  
> +/**
> + * vkms_config_plane_set_name() - Set the plane name
> + * @plane_cfg: Plane to set the name to
> + * @name: New plane name. The name is copied.
> + */
> +static inline void
> +vkms_config_plane_set_name(struct vkms_config_plane *plane_cfg,
> +			   const char *name)
> +{
> +	if (plane_cfg->name)
> +		kfree_const(plane_cfg->name);
> +	plane_cfg->name = kstrdup_const(name, GFP_KERNEL);
> +}
> +
> +/**
> + * vkms_config_plane_get_name - Get the plane name
> + * @plane_cfg: Plane to get the name from
> + */
> +static inline const char *
> +vkms_config_plane_get_name(const struct vkms_config_plane *plane_cfg)
> +{
> +	return plane_cfg->name;
> +}
> +
>  /**
>   * vkms_config_plane_attach_crtc - Attach a plane to a CRTC
>   * @plane_cfg: Plane to attach
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index db260df1d4f6..9ad286f043b5 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -225,6 +225,7 @@ struct vkms_output {
>  };
>  
>  struct vkms_config;
> +struct vkms_config_plane;
>  
>  /**
>   * struct vkms_device - Description of a VKMS device
> @@ -298,10 +299,10 @@ int vkms_output_init(struct vkms_device *vkmsdev);
>   * vkms_plane_init() - Initialize a plane
>   *
>   * @vkmsdev: VKMS device containing the plane
> - * @type: type of plane to initialize
> + * @config: plane configuration
>   */
>  struct vkms_plane *vkms_plane_init(struct vkms_device *vkmsdev,
> -				   enum drm_plane_type type);
> +				   struct vkms_config_plane *config);
>  
>  /* CRC Support */
>  const char *const *vkms_get_crc_sources(struct drm_crtc *crtc,
> diff --git a/drivers/gpu/drm/vkms/vkms_output.c b/drivers/gpu/drm/vkms/vkms_output.c
> index 2ee3749e2b28..22208d02afa4 100644
> --- a/drivers/gpu/drm/vkms/vkms_output.c
> +++ b/drivers/gpu/drm/vkms/vkms_output.c
> @@ -19,11 +19,7 @@ int vkms_output_init(struct vkms_device *vkmsdev)
>  		return -EINVAL;
>  
>  	vkms_config_for_each_plane(vkmsdev->config, plane_cfg) {
> -		enum drm_plane_type type;
> -
> -		type = vkms_config_plane_get_type(plane_cfg);
> -
> -		plane_cfg->plane = vkms_plane_init(vkmsdev, type);
> +		plane_cfg->plane = vkms_plane_init(vkmsdev, plane_cfg);
>  		if (IS_ERR(plane_cfg->plane)) {
>  			DRM_DEV_ERROR(dev->dev, "Failed to init vkms plane\n");
>  			return PTR_ERR(plane_cfg->plane);
> diff --git a/drivers/gpu/drm/vkms/vkms_plane.c b/drivers/gpu/drm/vkms/vkms_plane.c
> index e592e47a5736..73180cbb78b1 100644
> --- a/drivers/gpu/drm/vkms/vkms_plane.c
> +++ b/drivers/gpu/drm/vkms/vkms_plane.c
> @@ -9,6 +9,7 @@
>  #include <drm/drm_gem_atomic_helper.h>
>  #include <drm/drm_gem_framebuffer_helper.h>
>  
> +#include "vkms_config.h"
>  #include "vkms_drv.h"
>  #include "vkms_formats.h"
>  
> @@ -217,7 +218,7 @@ static const struct drm_plane_helper_funcs vkms_plane_helper_funcs = {
>  };
>  
>  struct vkms_plane *vkms_plane_init(struct vkms_device *vkmsdev,
> -				   enum drm_plane_type type)
> +				   struct vkms_config_plane *config)
>  {
>  	struct drm_device *dev = &vkmsdev->drm;
>  	struct vkms_plane *plane;
> @@ -225,7 +226,8 @@ struct vkms_plane *vkms_plane_init(struct vkms_device *vkmsdev,
>  	plane = drmm_universal_plane_alloc(dev, struct vkms_plane, base, 0,
>  					   &vkms_plane_funcs,
>  					   vkms_formats, ARRAY_SIZE(vkms_formats),
> -					   NULL, type, NULL);
> +					   NULL, vkms_config_plane_get_type(config),
> +					   vkms_config_plane_get_name(config));
>  	if (IS_ERR(plane))
>  		return plane;
>  
> 
> -- 
> 2.51.0
>