Re: hal, udev and video4linux probers

[Kay Sievers <kay.sievers@vrfy.org>]

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On Fri, 2009-05-08 at 19:04 +0200, Filippo Argiolas wrote:
> Probably a dedicated Devicekit-video thing
> would be overengineered for a simple task like this, so udev-extras
> should be the new place for it.

If you want, try this:
  $ gcc -Wall -o v4l_id v4l_id.c
  $ cp v4l_id /lib/udev
  $ cp 70-v4l_id.rules /lib/udev/rules.d/

After you un-plugged/plugged a device, you will see the properties at
the device:
  /sbin/udevadm info --query=env --name=video0
  ...
  ID_V4L_VERSION=2
  ID_V4L_PRODUCT=UVC Camera (17ef:4807)
  ID_V4L_VIDEO_CAPTURE=1
  ...

> Being honest I'm not so sure I will use libudev, I'm currently looking
> for a way to do the device probing directly from gstreamer, but it
> would be nice to preserve that v4l probing stuff somewhere with HAL
> going away (furthermore, I doubt we're the only users of that prober).

No sure, how else you can get that information. :)

You can query that properties at program startup with libudev, by
"enumerate"-ing all video4linux devices.

You can listen to events for new devices with a "monitor", which
retrieves all new video4linux devices as soon as they are connected.

If the prober is what you are looking for, let me know, and I will put
it in udev-extras.

Cheers,
Kay

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#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/ioctl.h>
#include <linux/videodev.h>
#include <linux/videodev2.h>

int main (int argc, char *argv[])
{
	int fd;
	char *device;
	struct video_capability v1cap;
	struct v4l2_capability v2cap;

	device = argv[1];
	if (device == NULL)
		return 1;
	fd = open (device, O_RDONLY);
	if (fd < 0)
		return 2;

	if (ioctl (fd, VIDIOC_QUERYCAP, &v2cap) == 0) {
		printf("ID_V4L_VERSION=2\n");
		printf("ID_V4L_PRODUCT=%s\n", v2cap.card);
		if ((v2cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) > 0)
			printf("ID_V4L_VIDEO_CAPTURE=1\n");
		if ((v2cap.capabilities & V4L2_CAP_VIDEO_OUTPUT) > 0)
			printf("ID_V4L_VIDEO_OUTPUT=1\n");
		if ((v2cap.capabilities & V4L2_CAP_VIDEO_OVERLAY) > 0)
			printf("ID_V4L_VIDEO_OVERLAY=1\n");
		if ((v2cap.capabilities & V4L2_CAP_AUDIO) > 0)
			printf("ID_V4L_AUDIO=1\n");
		if ((v2cap.capabilities & V4L2_CAP_TUNER) > 0)
			printf("ID_V4L_TUNER=1\n");
		if ((v2cap.capabilities & V4L2_CAP_RADIO) > 0)
			printf("ID_V4L_RADIO=1\n");
	} else if (ioctl (fd, VIDIOCGCAP, &v1cap) == 0) {
		printf("ID_V4L_VERSION=1\n");
		printf("ID_V4L_PRODUCT=%s\n", v1cap.name);
		if ((v1cap.type & VID_TYPE_CAPTURE) > 0)
			printf("ID_V4L_VIDEO_CAPTURE=1\n");
		if ((v1cap.type & VID_TYPE_OVERLAY) > 0)
			printf("ID_V4L_VIDEO_OVERLAY=1\n");
		if (v1cap.audios > 0)
			printf("ID_V4L_AUDIO=1\n");
		if ((v1cap.type & VID_TYPE_TUNER) > 0)
			printf("ID_V4L_TUNER=1\n");
	}

	close (fd);
	return 0;
}

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# do not edit this file, it will be overwritten on update

ACTION=="add|change", SUBSYSTEM=="video4linux", ENV{MAJOR}=="?*", IMPORT{program}="v4l_id $tempnode"