Re: [PATCH 6/7] [media] gspca: fix a v4l2-compliance failure during VIDIOC_REQBUFS

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 09-03-16 17:03, Antonio Ospite wrote:
> When calling VIDIOC_REQBUFS v4l2-compliance fails with this message:
>
>    fail: v4l2-test-buffers.cpp(476): q.reqbufs(node, 1)
>    test VIDIOC_REQBUFS/CREATE_BUFS/QUERYBUF: FAIL
>
> By looking at the v4l2-compliance code the failure happens when trying
> to request V4L2_MEMORY_USERPTR buffers without freeing explicitly the
> previously allocated V4L2_MEMORY_MMAP buffers.
>
> This would suggest that when changing the memory field in struct
> v4l2_requestbuffers the driver is supposed to free automatically any
> previous allocated buffers, and looking for inspiration at the code in
> drivers/media/v4l2-core/videobuf2-core.c::vb2_core_reqbufs() seems to
> confirm this interpretation; however gspca is just returning -EBUSY in
> this case.
>
> Removing the special handling for the case of a different memory value
> fixes the compliance failure.
>
> Signed-off-by: Antonio Ospite <ao2@ao2.it>
> ---
>
> This should be safe, but I'd really like a comment from someone with a more
> global knowledge of v4l2.
>
> If my interpretation about how drivers should behave when the value of the
> memory field changes is correct, I could send also a documentation update for
> Documentation/DocBook/media/v4l/vidioc-reqbufs.xml
>
> Just let me know.
>
> Thanks,
>     Antonio
>
>
>   drivers/media/usb/gspca/gspca.c | 7 -------
>   1 file changed, 7 deletions(-)
>
> diff --git a/drivers/media/usb/gspca/gspca.c b/drivers/media/usb/gspca/gspca.c
> index 84b0d6a..915b6c7 100644
> --- a/drivers/media/usb/gspca/gspca.c
> +++ b/drivers/media/usb/gspca/gspca.c
> @@ -1402,13 +1402,6 @@ static int vidioc_reqbufs(struct file *file, void *priv,
>   	if (mutex_lock_interruptible(&gspca_dev->queue_lock))
>   		return -ERESTARTSYS;
>
> -	if (gspca_dev->memory != GSPCA_MEMORY_NO
> -	    && gspca_dev->memory != GSPCA_MEMORY_READ
> -	    && gspca_dev->memory != rb->memory) {
> -		ret = -EBUSY;
> -		goto out;
> -	}
> -

reqbufs is used internally and this change will allow changing
gspca_dev->memory from USERPTR / MMAP to GSPCA_MEMORY_READ
please replace this check with a check to only allow
rb->memory to be GSPCA_MEMORY_READ when coming from GSPCA_MEMORY_NO
or GSPCA_MEMORY_READ

Regards,

Hans

>   	/* only one file may do the capture */
>   	if (gspca_dev->capt_file != NULL
>   	    && gspca_dev->capt_file != file) {
>