btrfs: Fix grossly misleading argument names in extent io search

The variables and function parameters of __etree_search which pertain to
prev/next are grossly misnamed. Namely, prev_ret holds the next state
and not the previous. Similarly, next_ret actually holds the previous
extent state relating to the offset we are interested in. Fix this by
renaming the variables as well as switching the arguments order. No
functional changes.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -281,8 +281,8 @@ static struct rb_node *tree_insert(struct rb_root *root,
 }
 
 static struct rb_node *__etree_search(struct extent_io_tree *tree, u64 offset,
-				      struct rb_node **prev_ret,
 				      struct rb_node **next_ret,
+				      struct rb_node **prev_ret,
 				      struct rb_node ***p_ret,
 				      struct rb_node **parent_ret)
 {
@@ -311,23 +311,23 @@ static struct rb_node *__etree_search(struct extent_io_tree *tree, u64 offset,
 	if (parent_ret)
 		*parent_ret = prev;
 
-	if (prev_ret) {
+	if (next_ret) {
 		orig_prev = prev;
 		while (prev && offset > prev_entry->end) {
 			prev = rb_next(prev);
 			prev_entry = rb_entry(prev, struct tree_entry, rb_node);
 		}
-		*prev_ret = prev;
+		*next_ret = prev;
 		prev = orig_prev;
 	}
 
-	if (next_ret) {
+	if (prev_ret) {
 		prev_entry = rb_entry(prev, struct tree_entry, rb_node);
 		while (prev && offset < prev_entry->start) {
 			prev = rb_prev(prev);
 			prev_entry = rb_entry(prev, struct tree_entry, rb_node);
 		}
-		*next_ret = prev;
+		*prev_ret = prev;
 	}
 	return NULL;
 }
@@ -338,12 +338,12 @@ tree_search_for_insert(struct extent_io_tree *tree,
 		       struct rb_node ***p_ret,
 		       struct rb_node **parent_ret)
 {
-	struct rb_node *prev = NULL;
+	struct rb_node *next= NULL;
 	struct rb_node *ret;
 
-	ret = __etree_search(tree, offset, &prev, NULL, p_ret, parent_ret);
+	ret = __etree_search(tree, offset, &next, NULL, p_ret, parent_ret);
 	if (!ret)
-		return prev;
+		return next;
 	return ret;
 }