work-around for video4linux sysfs

[Kees Cook <kees@ubuntu.com>]

Hi,

I proposed the change below while Kay and Scott were at GUADEC, and
it seems the response was generally negative, but without any better
suggestions.  I'd like to bring this up again, as I think this solution,
while being a bit of hack, should at least be forward-compatible if/when
v4l sysfs stuff is sorted out better.

These patches create a /dev/v4l/by-path tree so that devices can
be explicitly identified (I could find no other common-across-v4l
uniquely identifying information).  Explicit symlinks are needed since
initialization order between v4l sub-drivers isn't always in the same.
Things like MythTV get very upset when /dev/video0 and /dev/video1 swap
places, for example...

First are changes to extras/path_id/path_id to handle missing driver
links, followed by changes to the debian rule set, as an example of how
the changes to path_id could be used.

Suggestions, thoughts?

Thanks,

-Kees


--- udev-113~/extras/path_id/path_id	2007-07-18 11:07:15.000000000 -0700
+++ udev-113/extras/path_id/path_id	2007-07-18 11:08:05.000000000 -0700
@@ -551,6 +551,17 @@ handle_device () {
 			d="$d-${rewind}st${mode}"
 		fi
 	fi
+	# v4l sysfs tree doesn't include driver details
+	if [ "$TYPE" = "video4linux" ] ; then
+		if [ -e "$full_sysfs_device_path/driver" ]; then
+			cd "$full_sysfs_device_path"/driver
+			driver="`pwd -P`"
+			cd "$OPWD"
+			if [ -n "$driver" ]; then
+				d="${d}${driver##*/}"
+			fi
+		fi
+	fi
 }
 
 case "$TYPE" in
@@ -566,6 +577,10 @@ case "$TYPE" in
 		handle_device
 		echo "ID_PATH=$d"
 		;;
+	video4linux)
+		handle_device
+		echo "ID_PATH=$d"
+		;;
 	*)
 		RESULT=1
 		;;


diff -u udev-113/debian/rules.d/60-symlinks.rules udev-113/debian/rules.d/60-symlinks.rules
--- udev-113/debian/rules.d/60-symlinks.rules
+++ udev-113/debian/rules.d/60-symlinks.rules
@@ -16,0 +17,14 @@
+
+# Create video4linux PCI path symlinks
+ACTION!="add", GOTO="video4linux_path_end"
+SUBSYSTEM!="video4linux", GOTO="video4linux_path_end"
+
+IMPORT{program}="path_id %p"
+# This is limited to the first 10 video devices to avoid per-driver 
+# device duplication (like ivtv), since we have no way to distinguish
+# interfaces via sysfs in a driver-agnostic way yet.  If OPTIONS allowed
+# replacement, we could set link_priority to -%m to give preference to the
+# first v4l interface per physical device.
+ENV{ID_PATH}="?*", KERNEL="video[0-9]", SYMLINK+="v4l/by-path/$env{ID_PATH}"
+
+LABEL="video4linux_path_end"


-- 
Kees Cook

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