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

[Hans Verkuil]

On 15/01/2024 12:00, Hans Verkuil wrote:
> 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.

Never mind, this changes in the next patch.

That said, I would prefer to keep the q_num_buffers variable here and
use it in the min_t and index, and replace it in the next patch.

It is a bit confusing in this patch, it makes more sense in the next.

Regards,

	Hans

> 
> 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
>