On 26/05/20(Tue) 11:30, Ingo Feinerer wrote:
> video(1) supports reading frames from a webcam via mmap(). To inform the
> V4L2 device about the number of desired buffers containing the frames to
> be memory-mapped, a VIDIOC_REQBUFS ioctl call is used.
>
> At the moment the v4l2_requestbuffers struct used for the VIDIOC_REQBUFS ioctl
> is only partially initialized which leads to an invalid mmap for my webcam:
The kernel driver, uvideo(4) or utvfu(4) is responsible for the rest of
the initialization.
> video: mmap: Invalid argument
>
> With the following diff applied my camera works (only on EHCI ports with USB
> 3.0 disabled in BIOS but that is a different story).
I'm afraid this might mask a real bug. Did you try building a kernel
with UVIDEO_DEBUG and run it to see what the error is? The function
you're interested in is uvideo_reqbufs() which correspond to the
VIDIOC_REQBUFS ioctl(2).
> Index: video.c
> ===================================================================
> RCS file: /cvs/xenocara/app/video/video.c,v
> retrieving revision 1.29
> diff -u -p -r1.29 video.c
> --- video.c 6 Nov 2019 05:46:51 -0000 1.29
> +++ video.c 26 May 2020 09:14:39 -0000
> @@ -1354,6 +1354,8 @@ mmap_init(struct video *vid)
>
> /* request buffers */
> rb.count = MMAP_NUM_BUFS;
> + rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
> + rb.memory = V4L2_MEMORY_MMAP;
> r = ioctl(vid->dev.fd, VIDIOC_REQBUFS, &rb);
> if (r == -1) {
> warn("ioctl VIDIOC_REQBUFS");
>
