tools: firmware: check for distro fallback udev cancel rule

Some distributions (Debian, OpenSUSE) have a udev rule in place to cancel
all fallback mechanism uevents immediately. This would obviously
make it hard to test against the fallback mechanism test interface,
so we need to check for this.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/testing/selftests/firmware/fw_userhelper.sh

@@ -64,9 +64,33 @@ trap "test_finish" EXIT
 echo "ABCD0123" >"$FW"
 NAME=$(basename "$FW")
 
+DEVPATH="$DIR"/"nope-$NAME"/loading
+
 # Test failure when doing nothing (timeout works).
-echo 1 >/sys/class/firmware/timeout
-echo -n "$NAME" >"$DIR"/trigger_request
+echo -n 2 >/sys/class/firmware/timeout
+echo -n "nope-$NAME" >"$DIR"/trigger_request 2>/dev/null &
+
+# Give the kernel some time to load the loading file, must be less
+# than the timeout above.
+sleep 1
+if [ ! -f $DEVPATH ]; then
+	echo "$0: fallback mechanism immediately cancelled"
+	echo ""
+	echo "The file never appeared: $DEVPATH"
+	echo ""
+	echo "This might be a distribution udev rule setup by your distribution"
+	echo "to immediately cancel all fallback requests, this must be"
+	echo "removed before running these tests. To confirm look for"
+	echo "a firmware rule like /lib/udev/rules.d/50-firmware.rules"
+	echo "and see if you have something like this:"
+	echo ""
+	echo "SUBSYSTEM==\"firmware\", ACTION==\"add\", ATTR{loading}=\"-1\""
+	echo ""
+	echo "If you do remove this file or comment out this line before"
+	echo "proceeding with these tests."
+	exit 1
+fi
+
 if diff -q "$FW" /dev/test_firmware >/dev/null ; then
 	echo "$0: firmware was not expected to match" >&2
 	exit 1