zpool: remove redundant zpool->type string, const-ify zpool_get_type

Make the return type of zpool_get_type const; the string belongs to the
zpool driver and should not be modified.  Remove the redundant type field
in the struct zpool; it is private to zpool.c and isn't needed since
->driver->type can be used directly.  Add comments indicating strings must
be null-terminated.

Signed-off-by: Dan Streetman <ddstreet@ieee.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Seth Jennings <sjennings@variantweb.net>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/zpool.c

diff --git a/mm/zpool.c b/mm/zpool.c
index 8f670d3..13f524d 100644
--- a/mm/zpool.c
+++ b/mm/zpool.c
@@ -18,8 +18,6 @@
 #include <linux/zpool.h>
 
 struct zpool {
-	char *type;
-
 	struct zpool_driver *driver;
 	void *pool;
 	const struct zpool_ops *ops;
@@ -73,6 +71,7 @@
 }
 EXPORT_SYMBOL(zpool_unregister_driver);
 
+/* this assumes @type is null-terminated. */
 static struct zpool_driver *zpool_get_driver(char *type)
 {
 	struct zpool_driver *driver;
@@ -113,6 +112,8 @@
  * not be loaded, and calling @zpool_create_pool() with the pool type will
  * fail.
  *
+ * The @type string must be null-terminated.
+ *
  * Returns: true if @type pool is available, false if not
  */
 bool zpool_has_pool(char *type)
@@ -145,6 +146,8 @@
  *
  * Implementations must guarantee this to be thread-safe.
  *
+ * The @type and @name strings must be null-terminated.
+ *
  * Returns: New zpool on success, NULL on failure.
  */
 struct zpool *zpool_create_pool(char *type, char *name, gfp_t gfp,
@@ -174,7 +177,6 @@
 		return NULL;
 	}
 
-	zpool->type = driver->type;
 	zpool->driver = driver;
 	zpool->pool = driver->create(name, gfp, ops, zpool);
 	zpool->ops = ops;
@@ -208,7 +210,7 @@
  */
 void zpool_destroy_pool(struct zpool *zpool)
 {
-	pr_debug("destroying pool type %s\n", zpool->type);
+	pr_debug("destroying pool type %s\n", zpool->driver->type);
 
 	spin_lock(&pools_lock);
 	list_del(&zpool->list);
@@ -228,9 +230,9 @@
  *
  * Returns: The type of zpool.
  */
-char *zpool_get_type(struct zpool *zpool)
+const char *zpool_get_type(struct zpool *zpool)
 {
-	return zpool->type;
+	return zpool->driver->type;
 }
 
 /**