Re: [PATCH v14 54/56] media: v4l2: Add DELETE_BUFS ioctl

[Tomasz Figa]

On Tue, Oct 31, 2023 at 05:31:02PM +0100, Benjamin Gaignard wrote:
> VIDIOC_DELETE_BUFS ioctl allows to delete buffers from a queue.
> The number of buffers to delete in given by count field of
> struct v4l2_delete_buffers and the range start at the index
> specified in the same structure.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx>
> ---
>  .../userspace-api/media/v4l/user-func.rst     |  1 +
>  .../media/v4l/vidioc-delete-bufs.rst          | 80 +++++++++++++++++++
>  .../media/v4l/vidioc-reqbufs.rst              |  1 +
>  .../media/common/videobuf2/videobuf2-core.c   | 30 +++++++
>  .../media/common/videobuf2/videobuf2-v4l2.c   | 20 +++++
>  drivers/media/v4l2-core/v4l2-dev.c            |  1 +
>  drivers/media/v4l2-core/v4l2-ioctl.c          | 17 ++++
>  include/media/v4l2-ioctl.h                    |  4 +
>  include/media/videobuf2-core.h                | 12 +++
>  include/media/videobuf2-v4l2.h                | 13 +++
>  include/uapi/linux/videodev2.h                | 17 ++++
>  11 files changed, 196 insertions(+)
>  create mode 100644 Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst
> 
> diff --git a/Documentation/userspace-api/media/v4l/user-func.rst b/Documentation/userspace-api/media/v4l/user-func.rst
> index 15ff0bf7bbe6..3fd567695477 100644
> --- a/Documentation/userspace-api/media/v4l/user-func.rst
> +++ b/Documentation/userspace-api/media/v4l/user-func.rst
> @@ -17,6 +17,7 @@ Function Reference
>      vidioc-dbg-g-chip-info
>      vidioc-dbg-g-register
>      vidioc-decoder-cmd
> +    vidioc-delete-bufs
>      vidioc-dqevent
>      vidioc-dv-timings-cap
>      vidioc-encoder-cmd
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst
> new file mode 100644
> index 000000000000..4791df1395d6
> --- /dev/null
> +++ b/Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst
> @@ -0,0 +1,80 @@
> +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
> +.. c:namespace:: V4L
> +
> +.. _VIDIOC_DELETE_BUFS:
> +
> +************************
> +ioctl VIDIOC_DELETE_BUFS
> +************************
> +
> +Name
> +====
> +
> +VIDIOC_DELETE_BUFS - Deletes buffers from a queue
> +Drivers using this feature must expose the ``V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS``
> +capability on the queue :c:func:`VIDIOC_REQBUFS` or :c:func:`VIDIOC_CREATE_BUFS`
> +are invoked.
> +
> +Synopsis
> +========
> +
> +.. c:macro:: VIDIOC_DELETE_BUFs
> +
> +``int ioctl(int fd, VIDIOC_DELETE_BUFs, struct v4l2_delete_buffers *argp)``
> +
> +Arguments
> +=========
> +
> +``fd``
> +    File descriptor returned by :c:func:`open()`.
> +
> +``argp``
> +    Pointer to struct :c:type:`v4l2_delete_buffers`.
> +
> +Description
> +===========
> +
> +Applications can optionally call the :ref:`VIDIOC_DELETE_BUFS` ioctl to
> +delete buffers from a queue.
> +
> +.. c:type:: v4l2_delete_buffers
> +
> +.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
> +
> +.. flat-table:: struct v4l2_delete_buffers
> +    :header-rows:  0
> +    :stub-columns: 0
> +    :widths:       1 1 2
> +
> +    * - __u32
> +      - ``index``
> +      - The starting buffer index to delete.
> +    * - __u32
> +      - ``count``
> +      - The number of buffers to be deleted with indices 'index' until 'index + count - 1'.
> +        All buffers in this range must be valid and in DEQUEUED state.

I wonder if this wouldn't be an inconvenience for the userspace. Would
there be anything wrong with allowing ranges with holes?
(Agreed about the DEQUEUED part of course.)

> +        In error case errno is set to ``EINVAL`` error code and index returns the index of
> +        the invalid buffer.
> +        If count and index are set to 0 :ref:`VIDIOC_DELETE_BUFS` will return 0.

Hmm, do we care about index if count is zero?

> +    * - __u32
> +      - ``type``
> +      - Type of the stream or buffers, this is the same as the struct
> +	:c:type:`v4l2_format` ``type`` field. See
> +	:c:type:`v4l2_buf_type` for valid values.
> +    * - __u32
> +      - ``reserved``\ [13]
> +      - A place holder for future extensions. Drivers and applications
> +	must set the array to zero.
> +
> +Return Value
> +============
> +
> +On success 0 is returned, on error -1 and the ``errno`` variable is set
> +appropriately. The generic error codes are described at the
> +:ref:`Generic Error Codes <gen-errors>` chapter.
> +
> +EBUSY
> +    File I/O is in progress.
> +
> +EINVAL
> +    The buffer ``index`` doesn't exist in the queue.
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> index 0b3a41a45d05..14d4a49c2945 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> @@ -121,6 +121,7 @@ aborting or finishing any DMA in progress, an implicit
>  .. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF:
>  .. _V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS:
>  .. _V4L2-BUF-CAP-SUPPORTS-MAX-NUM-BUFFERS:
> +.. _V4L2-BUF-CAP-SUPPORTS-DELETE-BUFS:
>  
>  .. raw:: latex
>  
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index 010a8bca0240..7068930a0ba6 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -1665,6 +1665,36 @@ int vb2_core_prepare_buf(struct vb2_queue *q, struct vb2_buffer *vb, void *pb)
>  }
>  EXPORT_SYMBOL_GPL(vb2_core_prepare_buf);
>  
> +int vb2_core_delete_bufs(struct vb2_queue *q, unsigned int start, unsigned int count)
> +{
> +	unsigned int i, ret = 0;
> +
> +	if (start == 0 && count == 0)

I guess related to the earlier comment, but why do we care about start
being zero?

> +		return 0;
> +
> +	mutex_lock(&q->mmap_lock);
> +
> +	for (i = start; i < start + count && i < q->max_num_buffers; i++) {
> +		struct vb2_buffer *vb = vb2_get_buffer(q, i);
> +
> +		if (!vb) {
> +			ret = -EINVAL;
> +			goto unlock;
> +		}
> +		if (vb->state != VB2_BUF_STATE_DEQUEUED) {
> +			ret = -EINVAL;
> +			goto unlock;
> +		}
> +	}
> +	__vb2_queue_free(q, start, count);
> +	dprintk(q, 2, "buffers deleted\n");
> +
> +unlock:
> +	mutex_unlock(&q->mmap_lock);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(vb2_core_delete_bufs);
> +
>  /*
>   * vb2_start_streaming() - Attempt to start streaming.
>   * @q:		videobuf2 queue
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 56daf3b5b2ba..f003618efbc1 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -694,6 +694,8 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
>  	if (q->supports_requests)
>  		*caps |= V4L2_BUF_CAP_SUPPORTS_REQUESTS;
>  #endif
> +	if (q->supports_delete_bufs)
> +		*caps |= V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS;
>  }
>  
>  static void validate_memory_flags(struct vb2_queue *q,
> @@ -751,6 +753,12 @@ int vb2_prepare_buf(struct vb2_queue *q, struct media_device *mdev,
>  }
>  EXPORT_SYMBOL_GPL(vb2_prepare_buf);
>  
> +int vb2_delete_bufs(struct vb2_queue *q, struct v4l2_delete_buffers *d)
> +{
> +	return vb2_core_delete_bufs(q, d->index, d->count);
> +}
> +EXPORT_SYMBOL_GPL(vb2_delete_bufs);
> +
>  int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
>  {
>  	unsigned requested_planes = 1;
> @@ -1012,6 +1020,18 @@ EXPORT_SYMBOL_GPL(vb2_poll);
>  
>  /* vb2 ioctl helpers */
>  
> +int vb2_ioctl_delete_bufs(struct file *file, void *priv,
> +			  struct v4l2_delete_buffers *p)
> +{
> +	struct video_device *vdev = video_devdata(file);
> +
> +	if (vb2_queue_is_busy(vdev->queue, file))
> +		return -EBUSY;
> +
> +	return vb2_delete_bufs(vdev->queue, p);
> +}
> +EXPORT_SYMBOL_GPL(vb2_ioctl_delete_bufs);
> +
>  int vb2_ioctl_reqbufs(struct file *file, void *priv,
>  			  struct v4l2_requestbuffers *p)
>  {
> diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
> index f81279492682..215654fd6581 100644
> --- a/drivers/media/v4l2-core/v4l2-dev.c
> +++ b/drivers/media/v4l2-core/v4l2-dev.c
> @@ -720,6 +720,7 @@ static void determine_valid_ioctls(struct video_device *vdev)
>  		SET_VALID_IOCTL(ops, VIDIOC_PREPARE_BUF, vidioc_prepare_buf);
>  		SET_VALID_IOCTL(ops, VIDIOC_STREAMON, vidioc_streamon);
>  		SET_VALID_IOCTL(ops, VIDIOC_STREAMOFF, vidioc_streamoff);
> +		SET_VALID_IOCTL(ops, VIDIOC_DELETE_BUFS, vidioc_delete_bufs);
>  	}
>  
>  	if (is_vid || is_vbi || is_meta) {
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 4d90424cbfc4..e9dcf439f9f3 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -489,6 +489,13 @@ static void v4l_print_create_buffers(const void *arg, bool write_only)
>  	v4l_print_format(&p->format, write_only);
>  }
>  
> +static void v4l_print_delete_buffers(const void *arg, bool write_only)
> +{
> +	const struct v4l2_delete_buffers *p = arg;
> +
> +	pr_cont("index=%u, count=%u\n", p->index, p->count);
> +}
> +
>  static void v4l_print_streamparm(const void *arg, bool write_only)
>  {
>  	const struct v4l2_streamparm *p = arg;
> @@ -2161,6 +2168,15 @@ static int v4l_prepare_buf(const struct v4l2_ioctl_ops *ops,
>  	return ret ? ret : ops->vidioc_prepare_buf(file, fh, b);
>  }
>  
> +static int v4l_delete_bufs(const struct v4l2_ioctl_ops *ops,
> +			   struct file *file, void *fh, void *arg)
> +{
> +	struct v4l2_delete_buffers *delete = arg;
> +	int ret = check_fmt(file, delete->type);

Should we also have

	memset_after(delete, 0, type);

here similar to how other ioctl handlers clear the reserved fields?

> +
> +	return ret ? ret : ops->vidioc_delete_bufs(file, fh, delete);
> +}
> +
>  static int v4l_g_parm(const struct v4l2_ioctl_ops *ops,
>  				struct file *file, void *fh, void *arg)
>  {
> @@ -2910,6 +2926,7 @@ static const struct v4l2_ioctl_info v4l2_ioctls[] = {
>  	IOCTL_INFO(VIDIOC_ENUM_FREQ_BANDS, v4l_enum_freq_bands, v4l_print_freq_band, 0),
>  	IOCTL_INFO(VIDIOC_DBG_G_CHIP_INFO, v4l_dbg_g_chip_info, v4l_print_dbg_chip_info, INFO_FL_CLEAR(v4l2_dbg_chip_info, match)),
>  	IOCTL_INFO(VIDIOC_QUERY_EXT_CTRL, v4l_query_ext_ctrl, v4l_print_query_ext_ctrl, INFO_FL_CTRL | INFO_FL_CLEAR(v4l2_query_ext_ctrl, id)),
> +	IOCTL_INFO(VIDIOC_DELETE_BUFS, v4l_delete_bufs, v4l_print_delete_buffers, INFO_FL_PRIO | INFO_FL_QUEUE | INFO_FL_CLEAR(v4l2_delete_buffers, type)),
>  };
>  #define V4L2_IOCTLS ARRAY_SIZE(v4l2_ioctls)
>  
> diff --git a/include/media/v4l2-ioctl.h b/include/media/v4l2-ioctl.h
> index edb733f21604..55afbde54211 100644
> --- a/include/media/v4l2-ioctl.h
> +++ b/include/media/v4l2-ioctl.h
> @@ -163,6 +163,8 @@ struct v4l2_fh;
>   *	:ref:`VIDIOC_CREATE_BUFS <vidioc_create_bufs>` ioctl
>   * @vidioc_prepare_buf: pointer to the function that implements
>   *	:ref:`VIDIOC_PREPARE_BUF <vidioc_prepare_buf>` ioctl
> + * @vidioc_delete_bufs: pointer to the function that implements
> + *	:ref:`VIDIOC_DELETE_BUFS <vidioc_delete_bufs>` ioctl
>   * @vidioc_overlay: pointer to the function that implements
>   *	:ref:`VIDIOC_OVERLAY <vidioc_overlay>` ioctl
>   * @vidioc_g_fbuf: pointer to the function that implements
> @@ -422,6 +424,8 @@ struct v4l2_ioctl_ops {
>  				  struct v4l2_create_buffers *b);
>  	int (*vidioc_prepare_buf)(struct file *file, void *fh,
>  				  struct v4l2_buffer *b);
> +	int (*vidioc_delete_bufs)(struct file *file, void *fh,
> +				  struct v4l2_delete_buffers *d);
>  
>  	int (*vidioc_overlay)(struct file *file, void *fh, unsigned int i);
>  	int (*vidioc_g_fbuf)(struct file *file, void *fh,
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 288477075a0e..db3bd986624e 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -507,6 +507,7 @@ struct vb2_buf_ops {
>   * @supports_requests: this queue supports the Request API.
>   * @requires_requests: this queue requires the Request API. If this is set to 1,
>   *		then supports_requests must be set to 1 as well.
> + * @supports_delete_bufs: this queue supports DELETE_BUFS ioctl.
>   * @uses_qbuf:	qbuf was used directly for this queue. Set to 1 the first
>   *		time this is called. Set to 0 when the queue is canceled.
>   *		If this is 1, then you cannot queue buffers from a request.
> @@ -595,6 +596,7 @@ struct vb2_queue {
>  	unsigned int		   quirk_poll_must_check_waiting_for_buffers:1;
>  	unsigned int			supports_requests:1;
>  	unsigned int			requires_requests:1;
> +	unsigned int			supports_delete_bufs:1;
>  	unsigned int			uses_qbuf:1;
>  	unsigned int			uses_requests:1;
>  	unsigned int			allow_cache_hints:1;
> @@ -846,6 +848,16 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
>   */
>  int vb2_core_prepare_buf(struct vb2_queue *q, struct vb2_buffer *vb, void *pb);
>  
> +/**
> + * vb2_core_delete_bufs() -
> + * @q:		pointer to &struct vb2_queue with videobuf2 queue.
> + * @start:	first index of the range of buffers to delete.
> + * @count:	number of buffers to delete.
> + *
> + *  Return: returns zero on success; an error code otherwise.
> + */
> +int vb2_core_delete_bufs(struct vb2_queue *q, unsigned int start, unsigned int count);
> +
>  /**
>   * vb2_core_qbuf() - Queue a buffer from userspace
>   *
> diff --git a/include/media/videobuf2-v4l2.h b/include/media/videobuf2-v4l2.h
> index 5a845887850b..79cea8459f52 100644
> --- a/include/media/videobuf2-v4l2.h
> +++ b/include/media/videobuf2-v4l2.h
> @@ -118,6 +118,17 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create);
>   */
>  int vb2_prepare_buf(struct vb2_queue *q, struct media_device *mdev,
>  		    struct v4l2_buffer *b);
> +/**
> + * vb2_delete_bufs() - Delete buffers from the queue
> + *
> + * @q:		pointer to &struct vb2_queue with videobuf2 queue.
> + * @d:		delete parameter, passed from userspace to
> + *		&v4l2_ioctl_ops->vidioc_delete_bufs handler in driver
> + *
> + * The return values from this function are intended to be directly returned
> + * from &v4l2_ioctl_ops->vidioc_delete_bufs handler in driver.
> + */
> +int vb2_delete_bufs(struct vb2_queue *q, struct v4l2_delete_buffers *d);
>  
>  /**
>   * vb2_qbuf() - Queue a buffer from userspace
> @@ -334,6 +345,8 @@ int vb2_ioctl_streamon(struct file *file, void *priv, enum v4l2_buf_type i);
>  int vb2_ioctl_streamoff(struct file *file, void *priv, enum v4l2_buf_type i);
>  int vb2_ioctl_expbuf(struct file *file, void *priv,
>  	struct v4l2_exportbuffer *p);
> +int vb2_ioctl_delete_bufs(struct file *file, void *priv,
> +			  struct v4l2_delete_buffers *p);
>  
>  /* struct v4l2_file_operations helpers */
>  
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 13ddb5abf584..96e105149906 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -1036,6 +1036,7 @@ struct v4l2_requestbuffers {
>  #define V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF	(1 << 5)
>  #define V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS		(1 << 6)
>  #define V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS		(1 << 7)
> +#define V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS		(1 << 8)
>  
>  /**
>   * struct v4l2_plane - plane info for multi-planar buffers
> @@ -2622,6 +2623,20 @@ struct v4l2_create_buffers {
>  	__u32			reserved[5];
>  };
>  
> +/**
> + * struct v4l2_delete_buffers - VIDIOC_DELETE_BUFS argument
> + * @index:	the first buffer to be deleted
> + * @count:	number of buffers to delete
> + * @type:	enum v4l2_buf_type
> + * @reserved:	future extensions
> + */
> +struct v4l2_delete_buffers {
> +	__u32			index;
> +	__u32			count;
> +	__u32			type;
> +	__u32			reserved[13];
> +};
> +
>  /*
>   *	I O C T L   C O D E S   F O R   V I D E O   D E V I C E S
>   *
> @@ -2721,6 +2736,8 @@ struct v4l2_create_buffers {
>  #define VIDIOC_DBG_G_CHIP_INFO  _IOWR('V', 102, struct v4l2_dbg_chip_info)
>  
>  #define VIDIOC_QUERY_EXT_CTRL	_IOWR('V', 103, struct v4l2_query_ext_ctrl)
> +#define VIDIOC_DELETE_BUFS	_IOWR('V', 104, struct v4l2_delete_buffers)
> +
>  
>  /* Reminder: when adding new ioctls please add support for them to
>     drivers/media/v4l2-core/v4l2-compat-ioctl32.c as well! */

Do we also need to add support for the new ioctl in there?

Best regards,
Tomasz