+/*
+ * We track the state of the socket on a given connection using
+ * values defined below. The transition to a new socket state is
+ * handled by a function which verifies we aren't coming from an
+ * unexpected state.
+ *
+ * --------
+ * | NEW* | transient initial state
+ * --------
+ * | con_sock_state_init()
+ * v
+ * ----------
+ * | CLOSED | initialized, but no socket (and no
+ * ---------- TCP connection)
+ * ^ \
+ * | \ con_sock_state_connecting()
+ * | ----------------------
+ * | \
+ * + con_sock_state_closed() \
+ * |+--------------------------- \
+ * | \ \ \
+ * | ----------- \ \
+ * | | CLOSING | socket event; \ \
+ * | ----------- await close \ \
+ * | ^ \ |
+ * | | \ |
+ * | + con_sock_state_closing() \ |
+ * | / \ | |
+ * | / --------------- | |
+ * | / \ v v
+ * | / --------------
+ * | / -----------------| CONNECTING | socket created, TCP
+ * | | / -------------- connect initiated
+ * | | | con_sock_state_connected()
+ * | | v
+ * -------------
+ * | CONNECTED | TCP connection established
+ * -------------
+ *
+ * State values for ceph_connection->sock_state; NEW is assumed to be 0.
+ */
+
+#define CON_SOCK_STATE_NEW 0 /* -> CLOSED */
+#define CON_SOCK_STATE_CLOSED 1 /* -> CONNECTING */
+#define CON_SOCK_STATE_CONNECTING 2 /* -> CONNECTED or -> CLOSING */
+#define CON_SOCK_STATE_CONNECTED 3 /* -> CLOSING or -> CLOSED */
+#define CON_SOCK_STATE_CLOSING 4 /* -> CLOSED */
+
+/*
+ * connection states
+ */
+#define CON_STATE_CLOSED 1 /* -> PREOPEN */
+#define CON_STATE_PREOPEN 2 /* -> CONNECTING, CLOSED */
+#define CON_STATE_CONNECTING 3 /* -> NEGOTIATING, CLOSED */
+#define CON_STATE_NEGOTIATING 4 /* -> OPEN, CLOSED */
+#define CON_STATE_OPEN 5 /* -> STANDBY, CLOSED */
+#define CON_STATE_STANDBY 6 /* -> PREOPEN, CLOSED */
+
+/*
+ * ceph_connection flag bits
+ */
+#define CON_FLAG_LOSSYTX 0 /* we can close channel or drop
+ * messages on errors */
+#define CON_FLAG_KEEPALIVE_PENDING 1 /* we need to send a keepalive */
+#define CON_FLAG_WRITE_PENDING 2 /* we have data ready to send */
+#define CON_FLAG_SOCK_CLOSED 3 /* socket state changed to closed */
+#define CON_FLAG_BACKOFF 4 /* need to retry queuing delayed work */
+