/*
   * Copyright (c) 2006 Oracle.  All rights reserved.
   *
   * This software is available to you under a choice of one of two
   * licenses.  You may choose to be licensed under the terms of the GNU
   * General Public License (GPL) Version 2, available from the file
   * COPYING in the main directory of this source tree, or the
   * OpenIB.org BSD license below:
   *
   *     Redistribution and use in source and binary forms, with or
   *     without modification, are permitted provided that the following
   *     conditions are met:
   *
   *      - Redistributions of source code must retain the above
   *        copyright notice, this list of conditions and the following
   *        disclaimer.
   *
   *      - Redistributions in binary form must reproduce the above
   *        copyright notice, this list of conditions and the following
   *        disclaimer in the documentation and/or other materials
   *        provided with the distribution.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
   * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
   * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
   * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
   * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
   * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
   * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
   * SOFTWARE.
   *
   */
  #include <linux/kernel.h>
  #include <linux/random.h>
  #include <linux/export.h>
  
  #include "rds.h"
  
  /*
   * All of connection management is simplified by serializing it through
   * work queues that execute in a connection managing thread.
   *
   * TCP wants to send acks through sendpage() in response to data_ready(),
   * but it needs a process context to do so.
   *
   * The receive paths need to allocate but can't drop packets (!) so we have
   * a thread around to block allocating if the receive fast path sees an
   * allocation failure.
   */
  
  /* Grand Unified Theory of connection life cycle:
   * At any point in time, the connection can be in one of these states:
   * DOWN, CONNECTING, UP, DISCONNECTING, ERROR
   *
   * The following transitions are possible:
   *  ANY		  -> ERROR
   *  UP		  -> DISCONNECTING
   *  ERROR	  -> DISCONNECTING
   *  DISCONNECTING -> DOWN
   *  DOWN	  -> CONNECTING
   *  CONNECTING	  -> UP
   *
   * Transition to state DISCONNECTING/DOWN:
   *  -	Inside the shutdown worker; synchronizes with xmit path
   *	through RDS_IN_XMIT, and with connection management callbacks
   *	via c_cm_lock.
   *
   *	For receive callbacks, we rely on the underlying transport
   *	(TCP, IB/RDMA) to provide the necessary synchronisation.
   */
  struct workqueue_struct *rds_wq;
  EXPORT_SYMBOL_GPL(rds_wq);
  
  void rds_connect_complete(struct rds_connection *conn)
  {
  	if (!rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_UP)) {
  		printk(KERN_WARNING "%s: Cannot transition to state UP, "
  				"current state is %d
  ",
  				__func__,
  				atomic_read(&conn->c_state));
  		atomic_set(&conn->c_state, RDS_CONN_ERROR);
  		queue_work(rds_wq, &conn->c_down_w);
  		return;
  	}
  
  	rdsdebug("conn %p for %pI4 to %pI4 complete
  ",
  	  conn, &conn->c_laddr, &conn->c_faddr);
  
  	conn->c_reconnect_jiffies = 0;
  	set_bit(0, &conn->c_map_queued);
  	queue_delayed_work(rds_wq, &conn->c_send_w, 0);
  	queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
  }
  EXPORT_SYMBOL_GPL(rds_connect_complete);
  
  /*
   * This random exponential backoff is relied on to eventually resolve racing
   * connects.
   *
   * If connect attempts race then both parties drop both connections and come
   * here to wait for a random amount of time before trying again.  Eventually
   * the backoff range will be so much greater than the time it takes to
   * establish a connection that one of the pair will establish the connection
   * before the other's random delay fires.
   *
   * Connection attempts that arrive while a connection is already established
   * are also considered to be racing connects.  This lets a connection from
   * a rebooted machine replace an existing stale connection before the transport
   * notices that the connection has failed.
   *
   * We should *always* start with a random backoff; otherwise a broken connection
   * will always take several iterations to be re-established.
   */
  void rds_queue_reconnect(struct rds_connection *conn)
  {
  	unsigned long rand;
  
  	rdsdebug("conn %p for %pI4 to %pI4 reconnect jiffies %lu
  ",
  	  conn, &conn->c_laddr, &conn->c_faddr,
  	  conn->c_reconnect_jiffies);
  
  	set_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
  	if (conn->c_reconnect_jiffies == 0) {
  		conn->c_reconnect_jiffies = rds_sysctl_reconnect_min_jiffies;
  		queue_delayed_work(rds_wq, &conn->c_conn_w, 0);
  		return;
  	}
  
  	get_random_bytes(&rand, sizeof(rand));
  	rdsdebug("%lu delay %lu ceil conn %p for %pI4 -> %pI4
  ",
  		 rand % conn->c_reconnect_jiffies, conn->c_reconnect_jiffies,
  		 conn, &conn->c_laddr, &conn->c_faddr);
  	queue_delayed_work(rds_wq, &conn->c_conn_w,
  			   rand % conn->c_reconnect_jiffies);
  
  	conn->c_reconnect_jiffies = min(conn->c_reconnect_jiffies * 2,
  					rds_sysctl_reconnect_max_jiffies);
  }
  
  void rds_connect_worker(struct work_struct *work)
  {
  	struct rds_connection *conn = container_of(work, struct rds_connection, c_conn_w.work);
  	int ret;
  
  	clear_bit(RDS_RECONNECT_PENDING, &conn->c_flags);
  	if (rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING)) {
  		ret = conn->c_trans->conn_connect(conn);
  		rdsdebug("conn %p for %pI4 to %pI4 dispatched, ret %d
  ",
  			conn, &conn->c_laddr, &conn->c_faddr, ret);
  
  		if (ret) {
  			if (rds_conn_transition(conn, RDS_CONN_CONNECTING, RDS_CONN_DOWN))
  				rds_queue_reconnect(conn);
  			else
  				rds_conn_error(conn, "RDS: connect failed
  ");
  		}
  	}
  }
  
  void rds_send_worker(struct work_struct *work)
  {
  	struct rds_connection *conn = container_of(work, struct rds_connection, c_send_w.work);
  	int ret;
  
  	if (rds_conn_state(conn) == RDS_CONN_UP) {
  		ret = rds_send_xmit(conn);
  		rdsdebug("conn %p ret %d
  ", conn, ret);
  		switch (ret) {
  		case -EAGAIN:
  			rds_stats_inc(s_send_immediate_retry);
  			queue_delayed_work(rds_wq, &conn->c_send_w, 0);
  			break;
  		case -ENOMEM:
  			rds_stats_inc(s_send_delayed_retry);
  			queue_delayed_work(rds_wq, &conn->c_send_w, 2);
  		default:
  			break;
  		}
  	}
  }
  
  void rds_recv_worker(struct work_struct *work)
  {
  	struct rds_connection *conn = container_of(work, struct rds_connection, c_recv_w.work);
  	int ret;
  
  	if (rds_conn_state(conn) == RDS_CONN_UP) {
  		ret = conn->c_trans->recv(conn);
  		rdsdebug("conn %p ret %d
  ", conn, ret);
  		switch (ret) {
  		case -EAGAIN:
  			rds_stats_inc(s_recv_immediate_retry);
  			queue_delayed_work(rds_wq, &conn->c_recv_w, 0);
  			break;
  		case -ENOMEM:
  			rds_stats_inc(s_recv_delayed_retry);
  			queue_delayed_work(rds_wq, &conn->c_recv_w, 2);
  		default:
  			break;
  		}
  	}
  }
  
  void rds_shutdown_worker(struct work_struct *work)
  {
  	struct rds_connection *conn = container_of(work, struct rds_connection, c_down_w);
  
  	rds_conn_shutdown(conn);
  }
  
  void rds_threads_exit(void)
  {
  	destroy_workqueue(rds_wq);
  }
  
  int rds_threads_init(void)
  {
  	rds_wq = create_singlethread_workqueue("krdsd");
  	if (!rds_wq)
  		return -ENOMEM;
  
  	return 0;
  }