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Message-ID: <b7643c00-8d48-4597-955c-2684d2abc625@xs4all.nl>
Date: Wed, 24 Jan 2024 13:59:24 +0100
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Subject: Re: [PATCH v17 6/8] media: v4l2: Add DELETE_BUFS ioctl
Content-Language: en-US, nl
From: Hans Verkuil <hverkuil@xs4all.nl>
To: Benjamin Gaignard <benjamin.gaignard@collabora.com>, mchehab@kernel.org
Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
 kernel@collabora.com
References: <20240119094944.26763-1-benjamin.gaignard@collabora.com>
 <20240119094944.26763-7-benjamin.gaignard@collabora.com>
 <8a19487d-e903-4961-b56b-42079c9362b3@xs4all.nl>
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In-Reply-To: <8a19487d-e903-4961-b56b-42079c9362b3@xs4all.nl>
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On 24/01/2024 13:33, Hans Verkuil wrote:
> On 19/01/2024 10:49, 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@collabora.com>
>> ---
>> version 17:
>> - rework DELETE_BUFS documentation
>>
>>  .../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   | 42 ++++++++++
>>  .../media/common/videobuf2/videobuf2-v4l2.c   | 20 +++++
>>  drivers/media/v4l2-core/v4l2-dev.c            |  1 +
>>  drivers/media/v4l2-core/v4l2-ioctl.c          | 20 +++++
>>  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, 211 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..d409063ceb3f
>> --- /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
>> +
>> +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.
>> +This ioctl is available if the ``V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS`` capability
>> +is set on the queue when :c:func:`VIDIOC_REQBUFS` or :c:func:`VIDIOC_CREATE_BUFS`
>> +are invoked.
>> +
>> +.. 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.
>> +        If count is set to 0 :ref:`VIDIOC_DELETE_BUFS` will do nothing and return 0.
>> +    * - __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.
>> +    Any buffer in range ``index`` to ``index + count - 1`` is not in
>> +    DEQUEUED state.
>> +
>> +EINVAL
>> +    Any buffer in range ``index`` to ``index + count - 1`` 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 010505ed92e8..99e631233a54 100644
>> --- a/drivers/media/common/videobuf2/videobuf2-core.c
>> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
>> @@ -1688,6 +1688,48 @@ 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;
>> +	unsigned int q_num_bufs = vb2_get_num_buffers(q);
>> +
>> +	if (count == 0)
>> +		return 0;
>> +
>> +	if (count > q_num_bufs)
>> +		return -EINVAL;
>> +
>> +	if (start + count > q->max_num_buffers)
> 
> Change this to:
> 
> 	if (start > q->max_num_buffers - count)
> 
> This avoids the corner case where 'start + count' overflows the unsigned int.
> 
>> +		return -EINVAL;
>> +
>> +	/* If streaming keep at least min_queued_buffers + 1 buffers */
>> +	if (q->streaming && (q_num_bufs - count < q->min_queued_buffers + 1))
>> +		return -EINVAL;
> 
> I would drop this. This will be caught automatically by the next check
> since if a driver needs q->min_queued_buffers to start the DMA, then
> once the DMA stated there will always be that amount of buffers in a
> non-DEQUEUED state.
> 
>> +
>> +	mutex_lock(&q->mmap_lock);
>> +
>> +	/* Check that all buffers in the range exist */
>> +	for (i = start; i < start + count; i++) {
>> +		struct vb2_buffer *vb = vb2_get_buffer(q, i);
>> +
>> +		if (!vb) {
>> +			ret = -EINVAL;
>> +			goto unlock;
>> +		}
>> +		if (vb->state != VB2_BUF_STATE_DEQUEUED) {
>> +			ret = -EBUSY;
>> +			goto unlock;
>> +		}
>> +	}
>> +	__vb2_queue_free(q, start, count);
>> +	dprintk(q, 2, "%u buffers deleted\n", count);
>> +
>> +unlock:
>> +	mutex_unlock(&q->mmap_lock);
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(vb2_core_delete_bufs);
> 
> There is one specific corner case here that needs attention: if ALL buffers
> are deleted (something that is possible if STREAMON was called, but no
> buffers are queued), then vb2_is_busy will suddenly return false.
> 
> This can have all sorts of subtle consequences since it is now possible
> to, for example, change the format.
> 
> There are two options here:
> 
> 1) vb2_is_busy() shouldn't check if there are buffers allocated, instead it
>    should check if buffers were allocated at least once. So calling REQBUFS
>    or CREATE_BUFS for the first time will set a flag to 1, until you call
>    REQBUFS with count 0, or close the filehandle. Deleting all buffers with
>    DELETE_BUFS will not change that.
> 
> 2) We treat deleting all buffers with DELETE_BUFS the same as calling REQBUFS(0),
>    in which case the code above needs to change.
> 
> I lean towards option 1. My reasoning is that REQBUFS does an implicit STREAMOFF,
> and DELETE_BUFS does not and I do not think DELETE_BUFS should allow vb2_is_busy()
> to become false. It would still be nice if it can delete all buffers, but we
> would have to check if there are no other places where the number of allocated
> buffers is checked, when perhaps it really should use vb2_is_busy() instead.

If we go for 1, then it is probably best to add a new patch early in the patch
series that changes vb2_is_busy() from 'buffers are allocated' to 'at least one
buffer has been allocated at some time'.

Regards,

	Hans

> 
>> +
>>  /*
>>   * 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 03e8080a68a8..626b5283dfdb 100644
>> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
>> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
>> @@ -698,6 +698,8 @@ static void vb2_set_flags_and_caps(struct vb2_queue *q, u32 memory,
>>  		*caps |= V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS;
>>  	if (q->supports_requests)
>>  		*caps |= V4L2_BUF_CAP_SUPPORTS_REQUESTS;
>> +	if (q->supports_delete_bufs)
>> +		*caps |= V4L2_BUF_CAP_SUPPORTS_DELETE_BUFS;
>>  	if (max_num_bufs) {
>>  		*max_num_bufs = q->max_num_buffers;
>>  		*caps |= V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS;
>> @@ -743,6 +745,12 @@ 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);
>> +
> 
> I would not add this. Drivers that want to support this should implement
> vb2_ioctl_delete_bufs(). Eventually I want to get away from these non-vb2_ioctl_
> functions.
> 
>>  int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
>>  {
>>  	unsigned requested_planes = 1;
>> @@ -1001,6 +1009,18 @@ 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 d13954bd31fd..e764af2e29ff 100644
>> --- a/drivers/media/v4l2-core/v4l2-dev.c
>> +++ b/drivers/media/v4l2-core/v4l2-dev.c
>> @@ -722,6 +722,7 @@ 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 33076af4dfdb..9676cd758426 100644
>> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
>> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
>> @@ -489,6 +489,14 @@ 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("type=%s, index=%u, count=%u\n",
>> +		prt_names(p->type, v4l2_type_names), p->index, p->count);
>> +}
>> +
>>  static void v4l_print_streamparm(const void *arg, bool write_only)
>>  {
>>  	const struct v4l2_streamparm *p = arg;
>> @@ -2161,6 +2169,17 @@ 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);
>> +
>> +	memset_after(delete, 0, type);
> 
> I don't think this is needed since you use INFO_FL_CLEAR() below. That does it for you.
> 
>> +
>> +	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 +2929,7 @@ 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 8647eee348bd..4e62b31561d9 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.
>> @@ -613,6 +614,7 @@ 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;
> 
> I am not convinced we want do enable this per-queue. i will have
> to think some more about this.
> 
>>  	unsigned int			uses_qbuf:1;
>>  	unsigned int			uses_requests:1;
>>  	unsigned int			allow_cache_hints:1;
>> @@ -865,6 +867,16 @@ 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);
> 
> Drop this.
> 
>>  
>>  /**
>>   * 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 68e7ac178cc2..ce436f924782 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
>> @@ -2624,6 +2625,20 @@ 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
>>   *
>> @@ -2723,6 +2738,8 @@ 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! */
> 
> Regards,
> 
> 	Hans
>