collect_paths(): constify the return value

callers have no business modifying the paths they get

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Al Viro

fs/namespace.c

@@ -2300,7 +2300,7 @@ static inline bool extend_array(struct path **res, struct path **to_free,
 	return p;
 }
 
-struct path *collect_paths(const struct path *path,
+const struct path *collect_paths(const struct path *path,
 			      struct path *prealloc, unsigned count)
 {
 	struct mount *root = real_mount(path->mnt);
@@ -2334,7 +2334,7 @@ struct path *collect_paths(const struct path *path,
 	return res;
 }
 
-void drop_collected_paths(const struct path *paths, struct path *prealloc)
+void drop_collected_paths(const struct path *paths, const struct path *prealloc)
 {
 	for (const struct path *p = paths; p->mnt; p++)
 		path_put(p);

include/linux/mount.h

@@ -104,8 +104,8 @@ extern int may_umount_tree(struct vfsmount *);
 extern int may_umount(struct vfsmount *);
 int do_mount(const char *, const char __user *,
 		     const char *, unsigned long, void *);
-extern struct path *collect_paths(const struct path *, struct path *, unsigned);
-extern void drop_collected_paths(const struct path *, struct path *);
+extern const struct path *collect_paths(const struct path *, struct path *, unsigned);
+extern void drop_collected_paths(const struct path *, const struct path *);
 extern void kern_unmount_array(struct vfsmount *mnt[], unsigned int num);
 
 extern int cifs_root_data(char **dev, char **opts);