Hi Hans
On Thu, 7 Jun 2012, Hans Verkuil wrote:
> Hi all,
>
> I'm extending v4l2-compliance with support for VIDIOC_REQBUFS and VIDIOC_CREATE_BUFS,
> and I ran into an undefined issue: what happens if VIDIOC_CREATE_BUFS is called with
> count set to 0?
>
> I think there should be a separate test for that. Right now queue_setup will receive
> a request for 0 buffers, and I don't know if drivers expect a zero value there.
>
> I suggest that CREATE_BUFS with a count of 0 will only check whether memory and
> format.type are valid, and if they are it will just return 0 and do nothing.
Sounds good to me.
> Also note that this code in vb2_create_bufs is wrong:
>
> ret = __vb2_queue_alloc(q, create->memory, num_buffers,
> num_planes);
> if (ret < 0) {
> dprintk(1, "Memory allocation failed with error: %d\n", ret);
> return ret;
> }
>
> It should be:
>
> if (ret == 0) {
Indeed you're right. But then the return above should be "return -ENOMEM,"
shouldn't it?
>
> __vb2_queue_alloc() returns the number of buffers it managed to allocate,
> which is never < 0.
>
> I propose to add the patch included below.
>
> Comments are welcome!
>
> Regards,
>
> Hans
>
> diff --git a/drivers/media/video/videobuf2-core.c b/drivers/media/video/videobuf2-core.c
> index a0702fd..01a8312 100644
> --- a/drivers/media/video/videobuf2-core.c
> +++ b/drivers/media/video/videobuf2-core.c
> @@ -647,6 +647,9 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
> return -EINVAL;
> }
>
> + if (create->count == 0)
> + return 0;
> +
> if (q->num_buffers == VIDEO_MAX_FRAME) {
> dprintk(1, "%s(): maximum number of buffers already allocated\n",
> __func__);
> @@ -675,7 +678,7 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
> /* Finally, allocate buffers and video memory */
> ret = __vb2_queue_alloc(q, create->memory, num_buffers,
> num_planes);
> - if (ret < 0) {
> + if (ret == 0) {
> dprintk(1, "Memory allocation failed with error: %d\n", ret);
> return ret;
See above, should return an error code here.
> }
>
Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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