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

  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@collabora.com>
---
 .../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(-)
  

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@collabora.com>
> ---
>  .../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
  

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@collabora.com>
>> ---
>>  .../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
>
  

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@collabora.com>
> ---
>  .../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)
>   */
>  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);
> +
> +	*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,
> +				   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);

While reviewing this, I think I found a bug in the current code:

vb2_create_bufs() sets V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS, but
if p->count == 0, then that function isn't called...

>  	/*
>  	 * 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;

...instead it just falls in this 'if'.

It would be better to refactor this so that vb2_ioctl_create_bufs()
relies on vb2_create_bufs for most of the work.

The reason for the messy code is that if p->count == 0, then it
should ignore any EBUSY results, since that should always work.

Alternatively, just copy the code from vb2_create_bufs here so the
flag is properly set.

In any case, fixing this is a separate patch that should go to v6.8.

Regards,

	Hans

> +	}
>  	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
  

Le 15/01/2024 à 13:11, Hans Verkuil a écrit :
> 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@collabora.com>
>> ---
>>   .../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)
>>    */
>>   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);
>> +
>> +	*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,
>> +				   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);
> While reviewing this, I think I found a bug in the current code:
>
> vb2_create_bufs() sets V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS, but
> if p->count == 0, then that function isn't called...
>
>>   	/*
>>   	 * 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;
> ...instead it just falls in this 'if'.
>
> It would be better to refactor this so that vb2_ioctl_create_bufs()
> relies on vb2_create_bufs for most of the work.
>
> The reason for the messy code is that if p->count == 0, then it
> should ignore any EBUSY results, since that should always work.
>
> Alternatively, just copy the code from vb2_create_bufs here so the
> flag is properly set.
>
> In any case, fixing this is a separate patch that should go to v6.8.

Do you want this new patch to be in the next version of this series or completely
separated ?

Regards,
Benjamin

>
> Regards,
>
> 	Hans
>
>> +	}
>>   	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
  

On 15/01/2024 15:52, Benjamin Gaignard wrote:
> 
> Le 15/01/2024 à 13:11, Hans Verkuil a écrit :
>> 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@collabora.com>
>>> ---
>>>   .../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)
>>>    */
>>>   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);
>>> +
>>> +    *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,
>>> +                   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);
>> While reviewing this, I think I found a bug in the current code:
>>
>> vb2_create_bufs() sets V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS, but
>> if p->count == 0, then that function isn't called...
>>
>>>       /*
>>>        * 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;
>> ...instead it just falls in this 'if'.
>>
>> It would be better to refactor this so that vb2_ioctl_create_bufs()
>> relies on vb2_create_bufs for most of the work.
>>
>> The reason for the messy code is that if p->count == 0, then it
>> should ignore any EBUSY results, since that should always work.
>>
>> Alternatively, just copy the code from vb2_create_bufs here so the
>> flag is properly set.
>>
>> In any case, fixing this is a separate patch that should go to v6.8.
> 
> Do you want this new patch to be in the next version of this series or completely
> separated ?

Completely separate. It's a fix that needs to go to v6.8.

Please prioritize this, once rc1 is released I'll prepare a PR with
several that need to go in v6.8.

Regards,

	Hans

> 
> Regards,
> Benjamin
> 
>>
>> Regards,
>>
>>     Hans
>>
>>> +    }
>>>       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
  

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@collabora.com>
> ---
>  .../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)
>   */
>  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);
> +
> +	*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;

I'm thinking that after this 'if' it might be a good idea to add a:

	/* There shouldn't be any buffers allocated, so first_index == 0 */
	WARN_ON(first_index);

Just as a sanity check.

Regards,

	Hans

> @@ -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,
> +				   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