Re: [PATCH v16 6/8] media: v4l2: Add DELETE_BUFS ioctl

[Benjamin Gaignard]

Le 15/01/2024 à 17:43, Hans Verkuil a écrit :
> On 15/12/2023 10:08, 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>
> > ---
> > version 16:
> > - Take care of 'min_queued_buffers' when deleting buffers
> > - Add more check about buffers range limit when deleting buffers.
> >
> >   .../userspace-api/media/v4l/user-func.rst     |  1 +
> >   .../media/v4l/vidioc-delete-bufs.rst          | 79 +++++++++++++++++++
> >   .../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          | 19 +++++
> >   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, 209 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..5d5326b063c0
> > --- /dev/null
> > +++ b/Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst
> > @@ -0,0 +1,79 @@
> > +.. 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
> The paragraph below does not belong here, it should be part of the description.
>
> > +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.
> You generally shouldn't talk about 'drivers'. Something like: "This ioctl is
> available if the ..." is better.
>
> > +
> > +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.
> > +        In error case errno is set to ``EINVAL`` error code.
> ?? You probably mean: In case of an error...
>
> I would actually drop this line altogether.
>
> > +        If count is set to 0 :ref:`VIDIOC_DELETE_BUFS` will return 0.
> ...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.
> > +
> > +EINVAL
> > +    The buffer ``index`` doesn't exist in the queue.
> This is incomplete: this is returned if any of the buffers in the range
> index to index+count-1 does not exist, or is not in the DEQUEUED state.
>
> Does it make sense that EINVAL is returned if a buffer is in the wrong
> state? Perhaps it should return EBUSY instead? I think that is more
> appropriate.

I will change that in the doc and in the code.

> > 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 67ce823a0196..3b32791e70a8 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-core.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> > @@ -1674,6 +1674,48 @@ 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)
> > +		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;
> Hmm, interesting.
>
> I will have to think some more about this. It would make the API more symmetrical
> if you can just delete all buffers (provided they are all DEQUEUED). But that has
> implications for functions like vb2_is_busy() that will now return false, even
> while you are streaming.
>
> > +
> > +	mutex_lock(&q->mmap_lock);
> > +
> > +	/* Check that all buffers in the range exist */
> > +	for (i = start; i < start + count && i < q->max_num_buffers; i++) {
> That test against q->max_num_buffers is not needed, it's already checked above.

You are right it is useless I will remove them.

> > +		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");
> I would report 'count' here as well, so you log how many buffers were
> actually deleted.
>
> > +
> > +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 3c0c423c5674..729641e004d2 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > @@ -686,6 +686,8 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
> >   		*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;
> >   }
> >   
> >   static void validate_memory_flags(struct vb2_queue *q,
> > @@ -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);
> > +
> >   int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
> >   {
> >   	unsigned requested_planes = 1;
> > @@ -1004,6 +1012,18 @@ 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..19af075cee6b 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);
> This should log 'type' as well.
>
> > +}
> > +
> >   static void v4l_print_streamparm(const void *arg, bool write_only)
> >   {
> >   	const struct v4l2_streamparm *p = arg;
> > @@ -2161,6 +2168,17 @@ 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);
> > +
> > +	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 +2928,7 @@ 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 e4c1fc7ae82f..7abdee874698 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.
> > @@ -612,6 +613,7 @@ 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;
> > @@ -864,6 +866,16 @@ 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 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)
> I'm not really certain if we need this cap. You can just call VIDIOC_DELETE_BUFS
> with 0 as count and index.

It is a flag per queue and getting the info like this avoid doing adding ioctl calls.
If I remember well it was also a request from Nicolas because it simplify userspace code,
testing one flag is simpler than calling ioctl why specify values.

Regards,
Benjamin

> >   
> >   /**
> >    * 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