Virtual V4L2 camera module.

This module will create a virtual v4l2 camera which will allow
feeding in frames from user space once streaming has started.

The device exposed for writing frames is /dev/vcamera and it
will be exposed once streaming has started.

TODO: A lot.

To manipulate the device:

  int fd = open("/dev/vcamera", O_RDWR);
  if (fd == -1) {
    perror("open");
    return 1;
  }

  struct v4l2_format fmt;
  struct v4l2_requestbuffers bufs;

  bzero(&fmt, sizeof(fmt));
  bzero(&bufs, sizeof(bufs));

  if (ioctl(fd, VIDIOC_G_FMT, &fmt) == -1) {
    perror("ioctl");
    return 1;
  }

  if (ioctl(fd, VIDIOC_REQBUFS, &bufs) == -1) {
    perror("ioctl");
    return 1;
  }

  printf("Kernel supplied:\n"
	 "Width: %i\n"
	 "Height: %i\n"
	 "Format: %i\n"
	 "Size: %i\n"
	 "Buffers: %i\n",
	 fmt.fmt.pix.width, fmt.fmt.pix.height, fmt.fmt.pix.pixelformat,
	 fmt.fmt.pix.sizeimage, bufs.count);

  char buf[fmt.fmt.pix.sizeimage];
  int fd2 = open("/path/to/data", O_RDONLY);
  if (fd2 == -1) {
    perror("open");
    return 1;
  }

  if (read(fd2, buf, fmt.fmt.pix.sizeimage) != fmt.fmt.pix.sizeimage) {
    perror("read");
    return 1;
  }

  while (1) {
    if (write(fd, buf, fmt.fmt.pix.sizeimage) != fmt.fmt.pix.sizeimage) {
      if (errno == EAGAIN) {
	continue;
      }

      perror("write");
      return 1;
    }
    break;
  }

  close(fd2);
  close(fd);
  return 0;