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>

Documentation/devices.txt

@@ -445,6 +445,7 @@ Your cooperation is appreciated.
 		233 = /dev/kmview	View-OS A process with a view
 		234 = /dev/btrfs-control	Btrfs control device
 		235 = /dev/autofs	Autofs control device
+		236 = /dev/mapper/control	Device-Mapper control device
 		240-254			Reserved for local use
 		255			Reserved for MISC_DYNAMIC_MINOR
 

drivers/md/dm-ioctl.c

@@ -1599,12 +1599,15 @@ static const struct file_operations _ctl_fops = {
 };
 
 static struct miscdevice _dm_misc = {
-	.minor 		= MISC_DYNAMIC_MINOR,
+	.minor		= MAPPER_CTRL_MINOR,
 	.name  		= DM_NAME,
-	.nodename	= "mapper/control",
+	.nodename	= DM_DIR "/" DM_CONTROL_NODE,
 	.fops  		= &_ctl_fops
 };
 
+MODULE_ALIAS_MISCDEV(MAPPER_CTRL_MINOR);
+MODULE_ALIAS("devname:" DM_DIR "/" DM_CONTROL_NODE);
+
 /*
  * Create misc character device and link to DM_DIR/control.
  */

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

include/linux/miscdevice.h

@@ -38,6 +38,7 @@
 #define KVM_MINOR		232
 #define BTRFS_MINOR		234
 #define AUTOFS_MINOR		235
+#define MAPPER_CTRL_MINOR	236
 #define MISC_DYNAMIC_MINOR	255
 
 struct device;