dm: allow autoloading of dm mod

Add devname:mapper/control and MAPPER_CTRL_MINOR module alias
to support dm-mod module autoloading.

Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Peter Rajnoha <prajnoha@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/include/linux/dm-ioctl.h b/include/linux/dm-ioctl.h
index 43b2de1..49eab36 100644
--- a/include/linux/dm-ioctl.h
+++ b/include/linux/dm-ioctl.h
@@ -11,6 +11,7 @@
 #include <linux/types.h>
 
 #define DM_DIR "mapper"		/* Slashes not supported */
+#define DM_CONTROL_NODE "control"
 #define DM_MAX_TYPE_NAME 16
 #define DM_NAME_LEN 128
 #define DM_UUID_LEN 129