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: Brandon Philips <bphilips@suse.de>
Signed-off-by: Kees Cook <kees@outflux.net>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/media/v4l2-dev.h b/include/media/v4l2-dev.h
index 40b0810a595a..9e6e4f18e948 100644
--- a/include/media/v4l2-dev.h
+++ b/include/media/v4l2-dev.h
@@ -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);