fix $attr{[<subsystem>/<sysname>]<attribute>} substitution

test/udev-test.pl

@@ -1654,6 +1654,16 @@ EOF
 		rules		=> <<EOF
 KERNEL=="sda", MODE="440"
 KERNEL=="sda", PROGRAM=="/bin/echo 0 0 0400letsdoabuffferoverflow0123456789012345789012345678901234567890", OWNER="%c{1}", GROUP="%c{2}", MODE="%c{3}"
+EOF
+	},
+	{
+		desc		=> "magic [subsys/sysname] attribute substitution",
+		subsys		=> "block",
+		devpath		=> "/devices/pci0000:00/0000:00:1f.2/host0/target0:0:0/0:0:0:0/block/sda",
+		exp_name	=> "sda-8741C4G-end",
+		exp_perms	=> "0:0:0660",
+		rules		=> <<EOF
+KERNEL=="sda", NAME="%k-%s{[dmi/id]product_name}-end"
 EOF
 	},
 

udev/udev-event.c

@@ -295,13 +295,17 @@ found:
 				size_t size;
 
 				value[0] = '\0';
+				/* read the value specified by [usb/]*/
 				util_resolve_subsys_kernel(event->udev, attr, value, sizeof(value), 1);
 
-				val = udev_device_get_sysattr_value(event->dev, attr);
-				if (val != NULL)
-					util_strlcpy(value, val, sizeof(value));
+				/* try to read attribute of the current device */
+				if (value[0] == '\0') {
+					val = udev_device_get_sysattr_value(event->dev, attr);
+					if (val != NULL)
+						util_strlcpy(value, val, sizeof(value));
+				}
 
-				/* try the current device, other matches may have selected */
+				/* try to read the attribute of the parent device, other matches have selected */
 				if (value[0] == '\0' && event->dev_parent != NULL && event->dev_parent != event->dev) {
 					val = udev_device_get_sysattr_value(event->dev_parent, attr);
 					if (val != NULL)