Re: [PATCH v2] drm/ioctl: Add a ioctl to label GEM objects

[Thierry Reding <thierry.reding@gmail.com>]

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On Thu, Sep 19, 2019 at 02:53:21PM +0200, Rohan Garg wrote:
> DRM_IOCTL_BO_SET_LABEL lets you label GEM objects, making it
> easier to debug issues in userspace applications.
> 
> Changes in v2:
>   - Hoist the IOCTL up into the drm_driver framework
> 
> Signed-off-by: Rohan Garg <rohan.garg@collabora.com>
> ---
>  drivers/gpu/drm/drm_gem.c      | 64 ++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_internal.h |  4 +++
>  drivers/gpu/drm/drm_ioctl.c    |  1 +
>  include/drm/drm_drv.h          | 18 ++++++++++
>  include/drm/drm_gem.h          |  7 ++++
>  include/uapi/drm/drm.h         | 20 +++++++++++
>  6 files changed, 114 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 6854f5867d51..785ac561619a 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -941,6 +941,65 @@ drm_gem_release(struct drm_device *dev, struct drm_file *file_private)
>  	idr_destroy(&file_private->object_idr);
>  }
>  
> +int drm_bo_set_label_ioctl(struct drm_device *dev, void *data,
> +		       struct drm_file *file_priv)

Perhaps call this drm_gem_set_label_ioctl() so that it's consistent with
the other GEM related IOCTLs?

> +{
> +	struct drm_label_object *args = data;

Similarly, perhaps make this struct drm_gem_set_label for consistency.

> +
> +	if (!args->len || !args->name)
> +		return -EINVAL;
> +
> +	if (dev->driver->label)
> +		return dev->driver->label(dev, args, file_priv);
> +
> +	return -EOPNOTSUPP;
> +}
> +
> +/**
> + * drm_gem_label - label a given GEM object
> + * @dev: drm_device for the associated GEM object
> + * @data: drm_label_bo struct with a label, label length and any relevant flags
> + * @file_private: drm file-private structure to clean up
> + */
> +
> +int drm_gem_set_label(struct drm_device *dev, struct drm_label_object *args, struct drm_file *file_priv)

Function name doesn't match the kerneldoc.

> +{
> +	struct drm_gem_object *gem_obj;
> +	int err = 0;
> +	char *label;
> +
> +	if (args->len > 0)
> +		label = strndup_user(u64_to_user_ptr(args->name), args->len);
> +
> +	gem_obj = drm_gem_object_lookup(file_priv, args->handle);
> +	if (!gem_obj) {
> +		DRM_ERROR("Failed to look up GEM BO %d\n", args->handle);

People could abuse this to spam the system logs with these error
messages. Better make this DRM_DEBUG() or leave it out completely.

> +		err = -ENOENT;
> +		goto err;

I think you're leaking the label string here.

> +	}
> +
> +	if ((args->len == 0 && args->name == NULL) || gem_obj->label) {
> +		kfree(gem_obj->label);
> +		gem_obj->label = NULL;
> +	}
> +
> +	gem_obj->label = label;
> +
> +	drm_gem_object_put_unlocked(gem_obj);
> +
> +	if (IS_ERR(gem_obj->label)) {
> +		err = PTR_ERR(gem_obj->label);
> +		goto err;
> +	}

Why don't you check for this earlier? That seems suboptimal because now
you've got some error value in gem_obj->label that you're going to have
to special case at every step of the way.

> +
> +err:
> +	if (err != 0)
> +		args->flags = err;

Why the flags? We typically just return the error...

> +
> +	return err;

... like here.

> +}

Do we want to export this so that drivers can use it?

> +
> +
>  /**
>   * drm_gem_object_release - release GEM buffer object resources
>   * @obj: GEM buffer object
> @@ -958,6 +1017,11 @@ drm_gem_object_release(struct drm_gem_object *obj)
>  
>  	dma_resv_fini(&obj->_resv);
>  	drm_gem_free_mmap_offset(obj);
> +
> +	if (obj->label) {
> +		kfree(obj->label);
> +		obj->label = NULL;
> +	}
>  }
>  EXPORT_SYMBOL(drm_gem_object_release);
>  
> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
> index 51a2055c8f18..8259622f9ab6 100644
> --- a/drivers/gpu/drm/drm_internal.h
> +++ b/drivers/gpu/drm/drm_internal.h
> @@ -137,6 +137,10 @@ int drm_gem_pin(struct drm_gem_object *obj);
>  void drm_gem_unpin(struct drm_gem_object *obj);
>  void *drm_gem_vmap(struct drm_gem_object *obj);
>  void drm_gem_vunmap(struct drm_gem_object *obj, void *vaddr);
> +int drm_bo_set_label_ioctl(struct drm_device *dev, void *data,
> +			struct drm_file *file_priv);
> +int drm_gem_set_label(struct drm_device *dev, struct drm_label_object *args,
> +			struct drm_file *file_priv);

This one seems to be unused now.

>  
>  /* drm_debugfs.c drm_debugfs_crc.c */
>  #if defined(CONFIG_DEBUG_FS)
> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
> index f675a3bb2c88..079d1422f9c5 100644
> --- a/drivers/gpu/drm/drm_ioctl.c
> +++ b/drivers/gpu/drm/drm_ioctl.c
> @@ -709,6 +709,7 @@ static const struct drm_ioctl_desc drm_ioctls[] = {
>  	DRM_IOCTL_DEF(DRM_IOCTL_MODE_LIST_LESSEES, drm_mode_list_lessees_ioctl, DRM_MASTER),
>  	DRM_IOCTL_DEF(DRM_IOCTL_MODE_GET_LEASE, drm_mode_get_lease_ioctl, DRM_MASTER),
>  	DRM_IOCTL_DEF(DRM_IOCTL_MODE_REVOKE_LEASE, drm_mode_revoke_lease_ioctl, DRM_MASTER),
> +	DRM_IOCTL_DEF(DRM_IOCTL_BO_SET_LABEL, drm_bo_set_label_ioctl, DRM_RENDER_ALLOW),
>  };
>  
>  #define DRM_CORE_IOCTL_COUNT	ARRAY_SIZE( drm_ioctls )
> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> index 8976afe48c1c..f736ba1f42a6 100644
> --- a/include/drm/drm_drv.h
> +++ b/include/drm/drm_drv.h
> @@ -715,6 +715,24 @@ struct drm_driver {
>  			    struct drm_device *dev,
>  			    uint32_t handle);
>  
> +
> +	/**
> +	 * @label:
> +	 *
> +	 * This label's a buffer object.
> +	 *
> +	 * Called by the user via ioctl.
> +	 *
> +	 * The default implementation is drm_gem_label(). GEM based drivers
> +	 * must not overwrite this.
> +

Spurious blank line.

> +	 * Returns:
> +	 *
> +	 * Zero on success, negative errno on failure.
> +	 */
> +	int (*label)(struct drm_device *dev, struct drm_label_object *args,
> +				struct drm_file *file_priv);

If I understand correctly, you use this so that non-GEM drivers can use
this IOCTL to label their non-GEM objects. Do you think that's really
useful? I mean they've already got quite a bit of special code to deal
with their objects, so singling out this IOCTL seems a bit odd.

Then again, I guess it doesn't really hurt since GEM-based drivers will
always use the standard implementation.

> +
>  	/**
>  	 * @gem_vm_ops: Driver private ops for this object
>  	 *
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index 6aaba14f5972..f801c054e972 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -237,6 +237,13 @@ struct drm_gem_object {
>  	 */
>  	int name;
>  
> +	/**
> +	 * @label:
> +	 *
> +	 * Label for this object, should be a human readable string.
> +	 */
> +	char *label;
> +
>  	/**
>  	 * @dma_buf:
>  	 *
> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> index 8a5b2f8f8eb9..23b507f5c571 100644
> --- a/include/uapi/drm/drm.h
> +++ b/include/uapi/drm/drm.h
> @@ -626,6 +626,25 @@ struct drm_gem_open {
>  	__u64 size;
>  };
>  
> +/** struct drm_label_object - ioctl argument for labelling BOs.
> + *
> + * This label's a BO with a userspace label
> + *
> + */
> +struct drm_label_object {
> +	/** Handle for the object being labelled. */
> +	__u32 handle;
> +
> +	/** Label and label length.
> +	 *  length includes the trailing NULL.

Nit: I think you mean "trailing NUL". Also, the parameter is called len
below, so the comment here should match.

Thierry

> +	 */
> +	__u32 len;
> +	__u64 name;
> +
> +	/** Flags */
> +	int flags;
> +};
> +
>  #define DRM_CAP_DUMB_BUFFER		0x1
>  #define DRM_CAP_VBLANK_HIGH_CRTC	0x2
>  #define DRM_CAP_DUMB_PREFERRED_DEPTH	0x3
> @@ -946,6 +965,7 @@ extern "C" {
>  #define DRM_IOCTL_SYNCOBJ_QUERY		DRM_IOWR(0xCB, struct drm_syncobj_timeline_array)
>  #define DRM_IOCTL_SYNCOBJ_TRANSFER	DRM_IOWR(0xCC, struct drm_syncobj_transfer)
>  #define DRM_IOCTL_SYNCOBJ_TIMELINE_SIGNAL	DRM_IOWR(0xCD, struct drm_syncobj_timeline_array)
> +#define DRM_IOCTL_BO_SET_LABEL      DRM_IOWR(0xCE, struct drm_label_object)
>  
>  /**
>   * Device specific ioctls should only be in their respective headers
> -- 
> 2.17.1
> 
> _______________________________________________
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> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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