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Date: Mon, 15 Jan 2024 16:17:18 +0100
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Subject: Re: [PATCH v16 3/8] media: core: Rework how create_buf index returned
 value is computed
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To: Benjamin Gaignard <benjamin.gaignard@collabora.com>, mchehab@kernel.org
Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
 kernel@collabora.com
References: <20231215090813.15610-1-benjamin.gaignard@collabora.com>
 <20231215090813.15610-4-benjamin.gaignard@collabora.com>
 <ea069946-adb2-4ab2-b40a-06d11846d9ee@xs4all.nl>
 <2d9296a1-1fbc-4d85-b147-90f8f10c8f5f@collabora.com>
From: Hans Verkuil <hverkuil@xs4all.nl>
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In-Reply-To: <2d9296a1-1fbc-4d85-b147-90f8f10c8f5f@collabora.com>
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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