1 files changed, 84 insertions, 0 deletions
diff --git a/kernel/servers.h b/kernel/servers.h
new file mode 100644
index 0000000..83d9b46
--- /dev/null
+++ b/kernel/servers.h
@@ -0,0 +1,84 @@
+/*
+ * kernel/servers.h
+ */
+
+
+#define SRTT_BETA       990
+#define SRTT_BETA_COMP   10
+#define SRTT_BETA_BASE 1000
+
+/*
+ * Though presented as a 16-bit number in sysfs, the SRTT is stored in
+ * an unsigned long, SRTT_SHIFT bits left-shifted.  This helps
+ * preserve the precision we need tou update the SRTTs.  If we stored
+ * SRTT in an integer, it would only be changed by RTTS *very* far
+ * away from it.
+ */
+#define SRTT_SHIFT       10
+
+/*
+ * After this interval without answering
+ * requests a server is considered down.
+ */
+#define TIMEOUT_STALLED 3*HZ
+
+
+/*
+ * Configure @srv_info based on @server: Create a socket, connect it
+ * and start a dnbd2_rx_loop for it.
+ */
+int add_server(dnbd2_server_t server, struct srv_info *srv_info);
+
+/*
+ * Reset @srv_info: Stop dnbd2_rx_loop, close the socket and zero all
+ * variables.
+ */
+void del_server(struct srv_info *srv_info);
+
+/*
+ * Look for an unused server-slot in @dev and configure it according
+ * to @server (using add_server). Nothing happens if the list of
+ * servers if full or if there is already a server in the list with
+ * the same IP and port as @server.
+ */
+void try_add_server(dnbd2_server_t server, dnbd2_device_t *dev);
+
+/*
+ * This function enqueues into the send-queue a request for the device
+ * capacity (CMD_GET_SIZE). This type of request is retransmitted
+ * every second. If an answer doesn't arrive within 4 seconds it
+ * assumes that the server is down.
+ */
+sector_t srv_get_capacity(struct srv_info *srv_info);
+
+/*
+ * Update min, max and srtt in @srv_info.
+ */
+void update_rtt(uint16_t rtt, struct srv_info *srv_info, uint16_t cmd);
+
+/*
+ * Enqueue a heartbeat request (CMD_GET_SERVERS) for @srv_info into
+ * the send-queue.
+ */
+void enqueue_hb(struct srv_info *srv_info);
+
+/*
+ * Schedule the removal of @srv_info to be processed by the global
+ * kernel workqueue as soon as possible. This function allows to
+ * trigger the removal of servers from within timers, in which
+ * sleeping is not allowed.
+ */
+void schedule_del_server(struct srv_info *srv_info);
+
+/*
+ * Schedule the search for a faster server:
+ * 1. Detect if the active server is stalled (down). In this case
+ *    switch to another server, if possible, and remove the old one
+ *    from the list.  If no servers are available to switch to
+ *    start the emergency mode.
+ * 2. If the emergency mode was not started go through the list of
+ *    servers and pick the one with the smallest SRTT.  If this
+ *    server meets our requirements (to_jiffies and to_percent)
+ *    switch to it.
+ */
+void schedule_activate_fastest(dnbd2_device_t *dev);