Commit 539a7555 authored by brandon@ifup.org's avatar brandon@ifup.org Committed by Mauro Carvalho Chehab
Browse files

V4L/DVB (8078): Introduce "index" attribute for persistent video4linux device nodes 



A number of V4L drivers have a mod param to specify their preferred minors.
This is because it is often desirable for applications to have a static /dev
name for a particular device.  However, using minors has several disadvantages:

  1) the requested minor may already be taken
  2) using a mod param is driver specific
  3) it requires every driver to add a param
  4) requires configuration by hand

This patch introduces an "index" attribute that when combined with udev rules
can create static device paths like this:

/dev/v4l/by-path/pci-0000\:00\:1d.2-usb-0\:1\:1.0-video0
/dev/v4l/by-path/pci-0000\:00\:1d.2-usb-0\:1\:1.0-video1
/dev/v4l/by-path/pci-0000\:00\:1d.2-usb-0\:1\:1.0-video2

$ ls -la /dev/v4l/by-path/pci-0000\:00\:1d.2-usb-0\:1\:1.0-video0
lrwxrwxrwx 1 root root 12 2008-04-28 00:02 /dev/v4l/by-path/pci-0000:00:1d.2-usb-0:1:1.0-video0 -> ../../video1

These paths are steady across reboots and should be resistant to rearranging
across Kernel versions.

video_register_device_index is available to drivers to request a
specific index number.

Signed-off-by: default avatarBrandon Philips <bphilips@suse.de>
Signed-off-by: default avatarKees Cook <kees@outflux.net>
Signed-off-by: default avatarKay Sievers <kay.sievers@vrfy.org>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@infradead.org>
parent bbfc4c23

drivers/media/video/videodev.c

+96 −2
Original line number Diff line number Diff line
@@ -372,6 +372,14 @@ EXPORT_SYMBOL(v4l_printk_ioctl); 
 *	sysfs stuff

 */



static ssize_t show_index(struct device *cd,

			 struct device_attribute *attr, char *buf)

{

	struct video_device *vfd = container_of(cd, struct video_device,

						class_dev);

	return sprintf(buf, "%i\n", vfd->index);

}



static ssize_t show_name(struct device *cd,

			 struct device_attribute *attr, char *buf)

{
@@ -410,6 +418,7 @@ static void video_release(struct device *cd) 


static struct device_attribute video_device_attrs[] = {

	__ATTR(name, S_IRUGO, show_name, NULL),

	__ATTR(index, S_IRUGO, show_index, NULL),

	__ATTR_NULL

};
@@ -1900,8 +1909,82 @@ int video_ioctl2 (struct inode *inode, struct file *file, 
}

EXPORT_SYMBOL(video_ioctl2);



struct index_info {

	struct device *dev;

	unsigned int used[VIDEO_NUM_DEVICES];

};



static int __fill_index_info(struct device *cd, void *data)

{

	struct index_info *info = data;

	struct video_device *vfd = container_of(cd, struct video_device,

						class_dev);



	if (info->dev == vfd->dev)

		info->used[vfd->index] = 1;



	return 0;

}



/**

 * assign_index - assign stream number based on parent device

 * @vdev: video_device to assign index number to, vdev->dev should be assigned

 * @num: -1 if auto assign, requested number otherwise

 *

 *

 * returns -ENFILE if num is already in use, a free index number if

 * successful.

 */

static int get_index(struct video_device *vdev, int num)

{

	struct index_info *info;

	int i;

	int ret = 0;



	if (num >= VIDEO_NUM_DEVICES)

		return -EINVAL;



	info = kzalloc(sizeof(*info), GFP_KERNEL);

	if (!info)

		return -ENOMEM;



	info->dev = vdev->dev;



	ret = class_for_each_device(&video_class, info,

					__fill_index_info);



	if (ret < 0)

		goto out;



	if (num >= 0) {

		if (!info->used[num])

			ret = num;

		else

			ret = -ENFILE;



		goto out;

	}



	for (i = 0; i < VIDEO_NUM_DEVICES; i++) {

		if (info->used[i])

			continue;

		ret = i;

		goto out;

	}



out:

	kfree(info);

	return ret;

}



static const struct file_operations video_fops;



int video_register_device(struct video_device *vfd, int type, int nr)

{

	return video_register_device_index(vfd, type, nr, -1);

}

EXPORT_SYMBOL(video_register_device);



/**

 *	video_register_device - register video4linux devices

 *	@vfd:  video device structure we want to register
@@ -1927,7 +2010,8 @@ static const struct file_operations video_fops; 
 *	%VFL_TYPE_RADIO - A radio card

 */



int video_register_device(struct video_device *vfd, int type, int nr)

int video_register_device_index(struct video_device *vfd, int type, int nr,

					int index)

{

	int i=0;

	int base;
@@ -1984,6 +2068,16 @@ int video_register_device(struct video_device *vfd, int type, int nr) 
	}

	video_device[i]=vfd;

	vfd->minor=i;



	ret = get_index(vfd, index);

	if (ret < 0) {

		printk(KERN_ERR "%s: get_index failed\n",

		       __func__);

		goto fail_minor;

	}



	vfd->index = ret;



	mutex_unlock(&videodev_lock);

	mutex_init(&vfd->lock);
@@ -2017,7 +2111,7 @@ int video_register_device(struct video_device *vfd, int type, int nr) 
	mutex_unlock(&videodev_lock);

	return ret;

}

EXPORT_SYMBOL(video_register_device);

EXPORT_SYMBOL(video_register_device_index);



/**

 *	video_unregister_device - unregister a video4linux device

include/media/v4l2-dev.h

+4 −0
Original line number Diff line number Diff line
@@ -96,6 +96,8 @@ struct video_device 
	int type;       /* v4l1 */

	int type2;      /* v4l2 */

	int minor;

	/* attribute to diferentiate multiple indexs on one physical device */

	int index;



	int debug;	/* Activates debug level*/
@@ -347,6 +349,8 @@ void *priv; 


/* Version 2 functions */

extern int video_register_device(struct video_device *vfd, int type, int nr);

int video_register_device_index(struct video_device *vfd, int type, int nr,

					int index);

void video_unregister_device(struct video_device *);

extern int video_ioctl2(struct inode *inode, struct file *file,

			  unsigned int cmd, unsigned long arg);