+static __u64 ptlrpc_last_xid;
+static spinlock_t ptlrpc_last_xid_lock;
+
+/* Initialize the XID for the node. This is common among all requests on
+ * this node, and only requires the property that it is monotonically
+ * increasing. It does not need to be sequential. Since this is also used
+ * as the RDMA match bits, it is important that a single client NOT have
+ * the same match bits for two different in-flight requests, hence we do
+ * NOT want to have an XID per target or similar.
+ *
+ * To avoid an unlikely collision between match bits after a client reboot
+ * (which would cause old to be delivered into the wrong buffer) we initialize
+ * the XID based on the current time, assuming a maximum RPC rate of 1M RPC/s.
+ * If the time is clearly incorrect, we instead use a 62-bit random number.
+ * In the worst case the random number will overflow 1M RPCs per second in
+ * 9133 years, or permutations thereof.
+ */
+#define YEAR_2004 (1ULL << 30)
+void ptlrpc_init_xid(void)
+{
+ time_t now = cfs_time_current_sec();
+
+ spin_lock_init(&ptlrpc_last_xid_lock);
+ if (now < YEAR_2004) {
+ ll_get_random_bytes(&ptlrpc_last_xid, sizeof(ptlrpc_last_xid));
+ ptlrpc_last_xid >>= 2;
+ ptlrpc_last_xid |= (1ULL << 61);
+ } else {
+ ptlrpc_last_xid = (now << 20);
+ }
+}