Re: [PATCH v16 3/8] media: core: Rework how create_buf index returned value is computed

[Hans Verkuil]

On 15/12/2023 10:08, Benjamin Gaignard wrote:
> When DELETE_BUFS will be introduced holes could created in bufs array.
> To be able to reuse these unused indices reworking how create->index
> is set is mandatory.
> Let __vb2_queue_alloc() decide which first index is correct and
> forward this to the caller.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx>
> ---
>  .../media/common/videobuf2/videobuf2-core.c   | 22 ++++++++++++-------
>  .../media/common/videobuf2/videobuf2-v4l2.c   | 20 +++++++++++------
>  include/media/videobuf2-core.h                |  5 ++++-
>  3 files changed, 31 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> index a183edf11586..cd2b9e51b9b0 100644
> --- a/drivers/media/common/videobuf2/videobuf2-core.c
> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> @@ -447,11 +447,12 @@ static void vb2_queue_remove_buffer(struct vb2_buffer *vb)
>   */

You should update the comment before this function to explain what is
returned in first_index.

>  static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
>  			     unsigned int num_buffers, unsigned int num_planes,
> -			     const unsigned plane_sizes[VB2_MAX_PLANES])
> +			     const unsigned int plane_sizes[VB2_MAX_PLANES],
> +			     unsigned int *first_index)
>  {
> -	unsigned int q_num_buffers = vb2_get_num_buffers(q);
>  	unsigned int buffer, plane;
>  	struct vb2_buffer *vb;
> +	unsigned long index;
>  	int ret;
>  
>  	/*
> @@ -459,7 +460,11 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
>  	 * in the queue is below q->max_num_buffers
>  	 */
>  	num_buffers = min_t(unsigned int, num_buffers,
> -			    q->max_num_buffers - q_num_buffers);
> +			    q->max_num_buffers - vb2_get_num_buffers(q));
> +
> +	index = vb2_get_num_buffers(q);

Perhaps move this line up, then you can use 'index' instead of
vb2_get_num_buffers() in the min_t line. Starting with the next
patch vb2_get_num_buffers becomes a more expensive operation.

General note: it is perhaps a good idea to check all the users of
vb2_get_num_buffers to make sure it is not called unnecessarily.

> +
> +	*first_index = index;
>  
>  	for (buffer = 0; buffer < num_buffers; ++buffer) {
>  		/* Allocate vb2 buffer structures */
> @@ -479,7 +484,7 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
>  			vb->planes[plane].min_length = plane_sizes[plane];
>  		}
>  
> -		vb2_queue_add_buffer(q, vb, q_num_buffers + buffer);
> +		vb2_queue_add_buffer(q, vb, index++);
>  		call_void_bufop(q, init_buffer, vb);
>  
>  		/* Allocate video buffer memory for the MMAP type */
> @@ -820,7 +825,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
>  	unsigned int q_num_bufs = vb2_get_num_buffers(q);
>  	unsigned plane_sizes[VB2_MAX_PLANES] = { };
>  	bool non_coherent_mem = flags & V4L2_MEMORY_FLAG_NON_COHERENT;
> -	unsigned int i;
> +	unsigned int i, first_index;
>  	int ret = 0;
>  
>  	if (q->streaming) {
> @@ -906,7 +911,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
>  
>  	/* Finally, allocate buffers and video memory */
>  	allocated_buffers =
> -		__vb2_queue_alloc(q, memory, num_buffers, num_planes, plane_sizes);
> +		__vb2_queue_alloc(q, memory, num_buffers, num_planes, plane_sizes, &first_index);
>  	if (allocated_buffers == 0) {
>  		dprintk(q, 1, "memory allocation failed\n");
>  		ret = -ENOMEM;
> @@ -980,7 +985,8 @@ EXPORT_SYMBOL_GPL(vb2_core_reqbufs);
>  int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
>  			 unsigned int flags, unsigned int *count,
>  			 unsigned int requested_planes,
> -			 const unsigned int requested_sizes[])
> +			 const unsigned int requested_sizes[],
> +			 unsigned int *first_index)
>  {
>  	unsigned int num_planes = 0, num_buffers, allocated_buffers;
>  	unsigned plane_sizes[VB2_MAX_PLANES] = { };
> @@ -1042,7 +1048,7 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
>  
>  	/* Finally, allocate buffers and video memory */
>  	allocated_buffers = __vb2_queue_alloc(q, memory, num_buffers,
> -				num_planes, plane_sizes);
> +				num_planes, plane_sizes, first_index);
>  	if (allocated_buffers == 0) {
>  		dprintk(q, 1, "memory allocation failed\n");
>  		ret = -ENOMEM;
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 54d572c3b515..3c0c423c5674 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -797,11 +797,16 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
>  	for (i = 0; i < requested_planes; i++)
>  		if (requested_sizes[i] == 0)
>  			return -EINVAL;
> -	return ret ? ret : vb2_core_create_bufs(q, create->memory,
> -						create->flags,
> -						&create->count,
> -						requested_planes,
> -						requested_sizes);
> +	if (ret)
> +		return ret;
> +
> +	ret = vb2_core_create_bufs(q, create->memory,

This can just be a direct 'return vb2_core_create_bufs(...'

> +				   create->flags,
> +				   &create->count,
> +				   requested_planes,
> +				   requested_sizes,
> +				   &create->index);
> +	return ret;
>  }
>  EXPORT_SYMBOL_GPL(vb2_create_bufs);
>  
> @@ -1029,15 +1034,16 @@ int vb2_ioctl_create_bufs(struct file *file, void *priv,
>  	int res = vb2_verify_memory_type(vdev->queue, p->memory,
>  			p->format.type);
>  
> -	p->index = vdev->queue->num_buffers;
>  	fill_buf_caps(vdev->queue, &p->capabilities);
>  	validate_memory_flags(vdev->queue, p->memory, &p->flags);
>  	/*
>  	 * If count == 0, then just check if memory and type are valid.
>  	 * Any -EBUSY result from vb2_verify_memory_type can be mapped to 0.
>  	 */
> -	if (p->count == 0)
> +	if (p->count == 0) {
> +		p->index = vb2_get_num_buffers(vdev->queue);
>  		return res != -EBUSY ? res : 0;
> +	}
>  	if (res)
>  		return res;
>  	if (vb2_queue_is_busy(vdev->queue, file))
> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> index 7b84b4e2e273..607f2ba7a905 100644
> --- a/include/media/videobuf2-core.h
> +++ b/include/media/videobuf2-core.h
> @@ -821,6 +821,8 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
>   * @count: requested buffer count.
>   * @requested_planes: number of planes requested.
>   * @requested_sizes: array with the size of the planes.
> + * @first_index: index of the first created buffer, all allocated buffers have
> + *		 indices in the range [first..first+count]
>   *
>   * Videobuf2 core helper to implement VIDIOC_CREATE_BUFS() operation. It is
>   * called internally by VB2 by an API-specific handler, like
> @@ -837,7 +839,8 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
>  int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
>  			 unsigned int flags, unsigned int *count,
>  			 unsigned int requested_planes,
> -			 const unsigned int requested_sizes[]);
> +			 const unsigned int requested_sizes[],
> +			 unsigned int *first_index);
>  
>  /**
>   * vb2_core_prepare_buf() - Pass ownership of a buffer from userspace

Regards,

	Hans