Message-ID: <814130d1-8597-d567-ddea-cb82cadea00f@xs4all.nl>
Date:   Tue, 5 Sep 2023 10:17:08 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        mchehab@...nel.org, tfiga@...omium.org, m.szyprowski@...sung.com,
        ming.qian@....com, ezequiel@...guardiasur.com.ar,
        p.zabel@...gutronix.de, gregkh@...uxfoundation.org,
        nicolas.dufresne@...labora.com
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-staging@...ts.linux.dev,
        kernel@...labora.com
Subject: Re: [PATCH v6 17/18] media: v4l2: Add DELETE_BUFS ioctl

On 01/09/2023 14:44, 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@...labora.com>
> ---
> v6:
> - Add lock in vb2_core_delete_buf()
> - Fix typo and comments
> - Add flags in VIDIOC_DELETE_BUFS decalaration
> 
>  .../userspace-api/media/v4l/user-func.rst     |  1 +
>  .../media/v4l/vidioc-delete-bufs.rst          | 73 +++++++++++++++++++
>  .../media/common/videobuf2/videobuf2-core.c   | 24 ++++++
>  .../media/common/videobuf2/videobuf2-v4l2.c   | 38 +++++++++-
>  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                |  9 +++
>  include/media/videobuf2-v4l2.h                | 11 +++
>  include/uapi/linux/videodev2.h                | 16 ++++
>  10 files changed, 193 insertions(+), 1 deletion(-)
>  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..a55fe6331fc8
> --- /dev/null
> +++ b/Documentation/userspace-api/media/v4l/vidioc-delete-bufs.rst
> @@ -0,0 +1,73 @@
> +.. 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.
> +
> +.. 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.

That's not quite correct. This function will delete the buffers with indices
index until index+count-1. And indices in that range have to be valid buffers,
i.e. you can't have already deleted buffers in that range.

Or should we allow that? It is a fair question.

All buffers also have to be in the DEQUEUED state.

The text above suggests that given the following valid indices:

0, 1, 3, 4 (so the buffer with index 2 was already deleted)

deleting 2 buffers from index 1 would delete buffers 1, 3. When in
fact it will attempt to delete buffers 1 and 2.

Also document explicitly that calling this with count=0 (and perhaps
index=0 as well?) can be used to check if this ioctl is supported.

> +    * - __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.

What should happen if you delete ALL buffers with this call? I.e., the
equivalent to REQBUFS with count=0.

Thinking about this the main difference is that DELETE_BUFS can only delete
dequeued buffers and it does not stop streaming if all buffers are deleted.

So REQBUFS with count=0 (or a STREAMOFF) is still needed to officially stop
streaming and cancel the queue.

Basically REQBUFS with count=0 is almost the equivalent of calling STREAMOFF followed
by DELETE_BUFS for all buffers. Almost, but not quite: REQBUFS(0) also reports
if the queue is unbalanced, and it sets q->num_buffers to 0. And in vb2_ioctl_reqbufs
it will set vdev->queue->owner to NULL.

I am inclined to do the same if DELETE_BUFS deletes all buffers.

> +
> +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/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index dc7f6b59d237..9edb2a1e95fc 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -1633,6 +1633,30 @@ 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_buf(struct vb2_queue *q, struct vb2_buffer *vb)
> +{
> +	mutex_lock(&q->mmap_lock);
> +	if (vb->planes[0].mem_priv)
> +		call_void_vb_qop(vb, buf_cleanup, vb);
> +
> +	/* Free MMAP buffers or release USERPTR buffers */
> +	if (q->memory == VB2_MEMORY_MMAP)
> +		__vb2_buf_mem_free(vb);
> +	else if (q->memory == VB2_MEMORY_DMABUF)
> +		__vb2_buf_dmabuf_put(vb);
> +	else
> +		__vb2_buf_userptr_put(vb);
> +
> +	vb2_queue_remove_buffer(q, vb);
> +	mutex_unlock(&q->mmap_lock);
> +
> +	dprintk(q, 2, "buffer %d deleted\n", vb->index);
> +	kfree(vb);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(vb2_core_delete_buf);

This is duplicating what already happens in __vb2_free_mem and __vb2_queue_free.

That code needs to be refactored.

What you want is a __vb2_delete_buffers(struct vb2_queue *q, unsigned int index, unsigned int buffers)
function that is called with mmap_lock held and that deletes buffers in the range 'index'
to 'index + count - 1'. Buffers may already be deleted.

__vb2_free_mem does almost do all of that already.

Then this new function can be called from __vb2_queue_free() and you can make
a vb2_core_delete_bufs() function that takes the lock and calls __vb2_delete_buffers.

Another note: currently __vb2_queue_free checks if any of the buffers had unbalanced
operations. That check needs to be moved to __vb2_delete_buffers as well otherwise
that would never be reported when using 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 8ba658ad9891..d0098f58a65c 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -385,7 +385,7 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct media_device *md
>  
>  	vb = vb2_get_buffer(q, b->index);
>  	if (!vb) {
> -		dprintk(q, 1, "%s: buffer is NULL\n", opname);
> +		dprintk(q, 1, "%s: buffer %u was deleted\n", opname, b->index);
>  		return -EINVAL;
>  	}
>  
> @@ -757,6 +757,42 @@ 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)
> +{
> +	struct vb2_buffer *vb;
> +	unsigned int index;
> +	int ret = 0;
> +

Add:

	if (!d->count)
		return 0;

(possibly also check if !d->index)

> +	if (d->index > q->num_buffers ||

> should be >= here.

> +	    d->count > q->num_buffers ||
> +	    (d->index + d->count) > q->num_buffers) {
> +		return -EINVAL;
> +	}

Once we can delete buffers, how does that change the meaning of num_buffers?
Isn't this really max_buffer_index or something similar? But we probably also
still need to keep track of the actual number of buffers.

And create_bufs still allocated buffers from the last index onwards, it does
not attempt to reuse indices of previously deleted buffers.

There are a lot of drivers that use num_buffers, they will have to be audited.

This needs a lot more thought.

> +
> +	for (index = d->index; index < d->index + d->count; index++) {
> +		vb = vb2_get_buffer(q, index);
> +		if (!vb) {
> +			dprintk(q, 1, "can't find the requested buffer\n");
> +			ret = -EINVAL;
> +			goto error;
> +		}
> +		if (vb->state != VB2_BUF_STATE_DEQUEUED) {
> +			dprintk(q, 1, "can't delete non dequeued buffer index %d\n", vb->index);
> +			ret = -EINVAL;
> +			goto error;
> +		}

These checks have to take place first, then, if all is OK, you call vb2_core_delete_bufs.

Actually, thinking this over, I would move all these checks to vb2_core_delete_bufs.

It can all be put under the mmap_lock mutex to ensure nobody is messing around
with the queue while this takes place.

Note that when vb2_core_reqbufs() is called with count=0, then if it sees that
a buffer is still in use (mmaped), it will log a debug message that the buffers
are orphaned. We should keep that, I believe.

> +
> +		ret = vb2_core_delete_buf(q, vb);
> +		if (ret)
> +			break;
> +	}
> +
> +error:
> +	d->index = index;

I wouldn't do this. I don't think this is useful.

> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(vb2_delete_bufs);
> +
>  int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
>  {
>  	unsigned requested_planes = 1;
> 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 f4d9d6279094..aac3a0ea0126 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=%d, count=%d\n", p->index, p->count);

Use %u since both args are unsigned.

> +}
> +
>  static void v4l_print_streamparm(const void *arg, bool write_only)
>  {
>  	const struct v4l2_streamparm *p = arg;
> @@ -2160,6 +2167,15 @@ 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);
> +
> +	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)
>  {
> @@ -2909,6 +2925,7 @@ 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 97153c69583f..e2c5ff31efd0 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -843,6 +843,15 @@ 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_buf() -
> + * @q: pointer to &struct vb2_queue with videobuf2 queue.
> + * @vb:		pointer to struct &vb2_buffer.
> + *
> + *  Return: returns zero on success; an error code otherwise.
> + */
> +int vb2_core_delete_buf(struct vb2_queue *q, struct vb2_buffer *vb);
> +
>  /**
>   * vb2_core_qbuf() - Queue a buffer from userspace
>   *
> diff --git a/include/media/videobuf2-v4l2.h b/include/media/videobuf2-v4l2.h
> index 5a845887850b..2ef68fdf388f 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);

I'm missing the vb2_ioctl_delete_bufs function with a call to vb2_queue_is_busy().

>  
>  /**
>   * vb2_qbuf() - Queue a buffer from userspace
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 78260e5d9985..9cc7f570d995 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -2616,6 +2616,20 @@ struct v4l2_create_buffers {
>  	__u32			reserved[6];
>  };
>  
> +/**
> + * 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
>   *
> @@ -2715,6 +2729,8 @@ 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! */

You need much more extensive compliance checks for this, esp. mixing
create_bufs and delete_bufs. And test it with the test-media test script.

Regards,

	Hans

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