-/* Opening and closing file handles. */
-void **fh_open (struct file_handle *, enum fh_referent mask,
- const char *type, const char *mode);
-int fh_close (struct file_handle *, const char *type, const char *mode);
-bool fh_is_open (const struct file_handle *);
+/* Mutual exclusion for access . */
+struct fh_lock *fh_lock (struct file_handle *, enum fh_referent mask,
+ const char *type, enum fh_access, bool exclusive);
+bool fh_unlock (struct fh_lock *);
+void *fh_lock_get_aux (const struct fh_lock *);
+void fh_lock_set_aux (struct fh_lock *, void *aux);
+bool fh_is_locked (const struct file_handle *, enum fh_access);