Whenever a device node is created some attributes are also created for you.
If you look in /sys/class/video4linux you see the devices. Go into e.g.
video0 and you will see 'name' and 'index' attributes. The 'name' attribute
-is the 'name' field of the video_device struct. The 'index' attribute is
-a device node index that can be assigned by the driver, or that is calculated
-for you.
-
-If you call video_register_device(), then the index is just increased by
-1 for each device node you register. The first video device node you register
-always starts off with 0.
+is the 'name' field of the video_device struct.
-Alternatively you can call video_register_device_index() which is identical
-to video_register_device(), but with an extra index argument. Here you can
-pass a specific index value (between 0 and 31) that should be used.
+The 'index' attribute is the index of the device node: for each call to
+video_register_device() the index is just increased by 1. The first video
+device node you register always starts with index 0.
Users can setup udev rules that utilize the index attribute to make fancy
device names (e.g. 'mpegX' for MPEG video capture device nodes).
- vfl_type: the device type passed to video_register_device.
- minor: the assigned device minor number.
- num: the device kernel number (i.e. the X in videoX).
-- index: the device index number (calculated or set explicitly using
- video_register_device_index).
+- index: the device index number.
If the registration failed, then you need to call video_device_release()
to free the allocated video_device struct, or free your own struct if the
};
/**
- * get_index - assign stream number based on parent device
+ * get_index - assign stream index number based on parent device
* @vdev: video_device to assign index number to, vdev->parent should be assigned
- * @num: -1 if auto assign, requested number otherwise
*
* Note that when this is called the new device has not yet been registered
- * in the video_device array.
+ * in the video_device array, but it was able to obtain a minor number.
*
- * Returns -ENFILE if num is already in use, a free index number if
- * successful.
+ * This means that we can always obtain a free stream index number since
+ * the worst case scenario is that there are VIDEO_NUM_DEVICES - 1 slots in
+ * use of the video_device array.
+ *
+ * Returns a free index number.
*/
-static int get_index(struct video_device *vdev, int num)
+static int get_index(struct video_device *vdev)
{
/* This can be static since this function is called with the global
videodev_lock held. */
static DECLARE_BITMAP(used, VIDEO_NUM_DEVICES);
int i;
- if (num >= VIDEO_NUM_DEVICES) {
- printk(KERN_ERR "videodev: %s num is too large\n", __func__);
- return -EINVAL;
- }
-
- /* Some drivers do not set the parent. In that case always return
- num or 0. */
+ /* Some drivers do not set the parent. In that case always return 0. */
if (vdev->parent == NULL)
- return num >= 0 ? num : 0;
+ return 0;
bitmap_zero(used, VIDEO_NUM_DEVICES);
}
}
- if (num >= 0) {
- if (test_bit(num, used))
- return -ENFILE;
- return num;
- }
-
- i = find_first_zero_bit(used, VIDEO_NUM_DEVICES);
- return i == VIDEO_NUM_DEVICES ? -ENFILE : i;
+ return find_first_zero_bit(used, VIDEO_NUM_DEVICES);
}
-int video_register_device(struct video_device *vdev, int type, int nr)
-{
- return video_register_device_index(vdev, type, nr, -1);
-}
-EXPORT_SYMBOL(video_register_device);
-
/**
- * video_register_device_index - register video4linux devices
+ * video_register_device - register video4linux devices
* @vdev: video device structure we want to register
* @type: type of device to register
* @nr: which device number (0 == /dev/video0, 1 == /dev/video1, ...
* -1 == first free)
- * @index: stream number based on parent device;
- * -1 if auto assign, requested number otherwise
*
* The registration code assigns minor numbers based on the type
* requested. -ENFILE is returned in all the device slots for this
*
* %VFL_TYPE_RADIO - A radio card
*/
-int video_register_device_index(struct video_device *vdev, int type, int nr,
- int index)
+int video_register_device(struct video_device *vdev, int type, int nr)
{
int i = 0;
int ret;
set_bit(nr, video_nums[type]);
/* Should not happen since we thought this minor was free */
WARN_ON(video_device[vdev->minor] != NULL);
- ret = vdev->index = get_index(vdev, index);
+ vdev->index = get_index(vdev);
mutex_unlock(&videodev_lock);
- if (ret < 0) {
- printk(KERN_ERR "%s: get_index failed\n", __func__);
- goto cleanup;
- }
-
/* Part 3: Initialize the character device */
vdev->cdev = cdev_alloc();
if (vdev->cdev == NULL) {
vdev->minor = -1;
return ret;
}
-EXPORT_SYMBOL(video_register_device_index);
+EXPORT_SYMBOL(video_register_device);
/**
* video_unregister_device - unregister a video4linux device
projects / ~andy / linux / commitdiff