flex_array: flex_array_prealloc takes a number of elements, not an end

Change flex_array_prealloc to take the number of elements for which space
should be allocated instead of the last (inclusive) element. Users
and documentation are updated accordingly.  flex_arrays got introduced before
they had users.  When folks started using it, they ended up needing a
different API than was coded up originally.  This swaps over to the API that
folks apparently need.

Based-on-patch-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
Tested-by: Chris Richards <gizmo@giz-works.com>
Acked-by: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: stable@kernel.org [2.6.38+]
diff --git a/include/linux/flex_array.h b/include/linux/flex_array.h
index 70e4efa..ebeb2f3 100644
--- a/include/linux/flex_array.h
+++ b/include/linux/flex_array.h
@@ -61,7 +61,7 @@
 struct flex_array *flex_array_alloc(int element_size, unsigned int total,
 		gfp_t flags);
 int flex_array_prealloc(struct flex_array *fa, unsigned int start,
-		unsigned int end, gfp_t flags);
+		unsigned int nr_elements, gfp_t flags);
 void flex_array_free(struct flex_array *fa);
 void flex_array_free_parts(struct flex_array *fa);
 int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,