dm: use kmem_cache macro

Use new KMEM_CACHE() macro and make the newly-exposed structure names more
meaningful.  Also remove some superfluous casts and inlines (let a modern
compiler be the judge).

Acked-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/md/dm-snap.h b/drivers/md/dm-snap.h
index 15fa2ae..650e0f1 100644
--- a/drivers/md/dm-snap.h
+++ b/drivers/md/dm-snap.h
@@ -30,7 +30,7 @@
  * An exception is used where an old chunk of data has been
  * replaced by a new one.
  */
-struct exception {
+struct dm_snap_exception {
 	struct list_head hash_list;
 
 	chunk_t old_chunk;
@@ -58,13 +58,13 @@
 	 * Find somewhere to store the next exception.
 	 */
 	int (*prepare_exception) (struct exception_store *store,
-				  struct exception *e);
+				  struct dm_snap_exception *e);
 
 	/*
 	 * Update the metadata with this exception.
 	 */
 	void (*commit_exception) (struct exception_store *store,
-				  struct exception *e,
+				  struct dm_snap_exception *e,
 				  void (*callback) (void *, int success),
 				  void *callback_context);