dm: export struct dm_dev

Split struct dm_dev in two and publish the part that other targets need in
include/linux/device-mapper.h.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index a90222e..178390d 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -13,7 +13,6 @@
 
 struct dm_target;
 struct dm_table;
-struct dm_dev;
 struct mapped_device;
 struct bio_vec;
 
@@ -84,6 +83,12 @@
  */
 void dm_set_device_limits(struct dm_target *ti, struct block_device *bdev);
 
+struct dm_dev {
+	struct block_device *bdev;
+	int mode;
+	char name[16];
+};
+
 /*
  * Constructors should call these functions to ensure destination devices
  * are opened/closed correctly.