+static int check_stateid_generation(stateid_t *in, stateid_t *ref)
+{
+ /* If the client sends us a stateid from the future, it's buggy: */
+ if (in->si_generation > ref->si_generation)
+ return nfserr_bad_stateid;
+ /*
+ * The following, however, can happen. For example, if the
+ * client sends an open and some IO at the same time, the open
+ * may bump si_generation while the IO is still in flight.
+ * Thanks to hard links and renames, the client never knows what
+ * file an open will affect. So it could avoid that situation
+ * only by serializing all opens and IO from the same open
+ * owner. To recover from the old_stateid error, the client
+ * will just have to retry the IO:
+ */
+ if (in->si_generation < ref->si_generation)
+ return nfserr_old_stateid;
+ return nfs_ok;
+}
+