+ * The locking rules are governed by the dio_lock_type parameter.
+ *
+ * DIO_NO_LOCKING (no locking, for raw block device access)
+ * For writes, i_sem is not held on entry; it is never taken.
+ *
+ * DIO_LOCKING (simple locking for regular files)
+ * For writes we are called under i_sem and return with i_sem held, even though
+ * it is internally dropped.
+ * For reads, i_sem is not held on entry, but it is taken and dropped before
+ * returning.