new helper: iterate_mounts()

apply function to vfsmounts in set returned by collect_mounts(),
stop if it returns non-zero.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8d53bc1..e764f24 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1794,7 +1794,8 @@
 extern long do_mount(char *, char *, char *, unsigned long, void *);
 extern struct vfsmount *collect_mounts(struct path *);
 extern void drop_collected_mounts(struct vfsmount *);
-
+extern int iterate_mounts(int (*)(struct vfsmount *, void *), void *,
+			  struct vfsmount *);
 extern int vfs_statfs(struct dentry *, struct kstatfs *);
 
 extern int current_umask(void);