text: // SPDX-License-Identifier: GPL-2.0-only
  /******************************************************************************
  *******************************************************************************
  **
  **  Copyright (C) Sistina Software, Inc.  1997-2003  All rights reserved.
  **  Copyright (C) 2004-2009 Red Hat, Inc.  All rights reserved.
  **
  **
  *******************************************************************************
  ******************************************************************************/
  
  /*
   * lowcomms.c
   *
   * This is the "low-level" comms layer.
   *
   * It is responsible for sending/receiving messages
   * from other nodes in the cluster.
   *
   * Cluster nodes are referred to by their nodeids. nodeids are
   * simply 32 bit numbers to the locking module - if they need to
   * be expanded for the cluster infrastructure then that is its
   * responsibility. It is this layer's
   * responsibility to resolve these into IP address or
   * whatever it needs for inter-node communication.
   *
   * The comms level is two kernel threads that deal mainly with
   * the receiving of messages from other nodes and passing them
   * up to the mid-level comms layer (which understands the
   * message format) for execution by the locking core, and
   * a send thread which does all the setting up of connections
   * to remote nodes and the sending of data. Threads are not allowed
   * to send their own data because it may cause them to wait in times
   * of high load. Also, this way, the sending thread can collect together
   * messages bound for one node and send them in one block.
   *
   * lowcomms will choose to use either TCP or SCTP as its transport layer
   * depending on the configuration variable 'protocol'. This should be set
   * to 0 (default) for TCP or 1 for SCTP. It should be configured using a
   * cluster-wide mechanism as it must be the same on all nodes of the cluster
   * for the DLM to function.
   *
   */
  
  #include <asm/ioctls.h>
  #include <net/sock.h>
  #include <net/tcp.h>
  #include <linux/pagemap.h>
  #include <linux/file.h>
  #include <linux/mutex.h>
  #include <linux/sctp.h>
  #include <linux/slab.h>
  #include <net/sctp/sctp.h>
  #include <net/ipv6.h>
  
  #include "dlm_internal.h"
  #include "lowcomms.h"
  #include "midcomms.h"
  #include "config.h"
  
  #define NEEDED_RMEM (4*1024*1024)
  #define CONN_HASH_SIZE 32
  
  /* Number of messages to send before rescheduling */
  #define MAX_SEND_MSG_COUNT 25
  
  struct cbuf {
  	unsigned int base;
  	unsigned int len;
  	unsigned int mask;
  };
  
  static void cbuf_add(struct cbuf *cb, int n)
  {
  	cb->len += n;
  }
  
  static int cbuf_data(struct cbuf *cb)
  {
  	return ((cb->base + cb->len) & cb->mask);
  }
  
  static void cbuf_init(struct cbuf *cb, int size)
  {
  	cb->base = cb->len = 0;
  	cb->mask = size-1;
  }
  
  static void cbuf_eat(struct cbuf *cb, int n)
  {
  	cb->len  -= n;
  	cb->base += n;
  	cb->base &= cb->mask;
  }
  
  static bool cbuf_empty(struct cbuf *cb)
  {
  	return cb->len == 0;
  }
  
  struct connection {
  	struct socket *sock;	/* NULL if not connected */
  	uint32_t nodeid;	/* So we know who we are in the list */
  	struct mutex sock_mutex;
  	unsigned long flags;
  #define CF_READ_PENDING 1
  #define CF_WRITE_PENDING 2
  #define CF_INIT_PENDING 4
  #define CF_IS_OTHERCON 5
  #define CF_CLOSE 6
  #define CF_APP_LIMITED 7
  #define CF_CLOSING 8
  	struct list_head writequeue;  /* List of outgoing writequeue_entries */
  	spinlock_t writequeue_lock;
  	int (*rx_action) (struct connection *);	/* What to do when active */
  	void (*connect_action) (struct connection *);	/* What to do to connect */
  	struct page *rx_page;
  	struct cbuf cb;
  	int retries;
  #define MAX_CONNECT_RETRIES 3
  	struct hlist_node list;
  	struct connection *othercon;
  	struct work_struct rwork; /* Receive workqueue */
  	struct work_struct swork; /* Send workqueue */
  };
  #define sock2con(x) ((struct connection *)(x)->sk_user_data)
  
  /* An entry waiting to be sent */
  struct writequeue_entry {
  	struct list_head list;
  	struct page *page;
  	int offset;
  	int len;
  	int end;
  	int users;
  	struct connection *con;
  };
  
  struct dlm_node_addr {
  	struct list_head list;
  	int nodeid;
  	int addr_count;
  	int curr_addr_index;
  	struct sockaddr_storage *addr[DLM_MAX_ADDR_COUNT];
  };
  
  static struct listen_sock_callbacks {
  	void (*sk_error_report)(struct sock *);
  	void (*sk_data_ready)(struct sock *);
  	void (*sk_state_change)(struct sock *);
  	void (*sk_write_space)(struct sock *);
  } listen_sock;
  
  static LIST_HEAD(dlm_node_addrs);
  static DEFINE_SPINLOCK(dlm_node_addrs_spin);
  
  static struct sockaddr_storage *dlm_local_addr[DLM_MAX_ADDR_COUNT];
  static int dlm_local_count;
  static int dlm_allow_conn;
  
  /* Work queues */
  static struct workqueue_struct *recv_workqueue;
  static struct workqueue_struct *send_workqueue;
  
  static struct hlist_head connection_hash[CONN_HASH_SIZE];
  static DEFINE_MUTEX(connections_lock);
  static struct kmem_cache *con_cache;
  
  static void process_recv_sockets(struct work_struct *work);
  static void process_send_sockets(struct work_struct *work);
  
  
  /* This is deliberately very simple because most clusters have simple
     sequential nodeids, so we should be able to go straight to a connection
     struct in the array */
  static inline int nodeid_hash(int nodeid)
  {
  	return nodeid & (CONN_HASH_SIZE-1);
  }
  
  static struct connection *__find_con(int nodeid)
  {
  	int r;
  	struct connection *con;
  
  	r = nodeid_hash(nodeid);
  
  	hlist_for_each_entry(con, &connection_hash[r], list) {
  		if (con->nodeid == nodeid)
  			return con;
  	}
  	return NULL;
  }
  
  /*
   * If 'allocation' is zero then we don't attempt to create a new
   * connection structure for this node.
   */
  static struct connection *__nodeid2con(int nodeid, gfp_t alloc)
  {
  	struct connection *con = NULL;
  	int r;
  
  	con = __find_con(nodeid);
  	if (con || !alloc)
  		return con;
  
  	con = kmem_cache_zalloc(con_cache, alloc);
  	if (!con)
  		return NULL;
  
  	r = nodeid_hash(nodeid);
  	hlist_add_head(&con->list, &connection_hash[r]);
  
  	con->nodeid = nodeid;
  	mutex_init(&con->sock_mutex);
  	INIT_LIST_HEAD(&con->writequeue);
  	spin_lock_init(&con->writequeue_lock);
  	INIT_WORK(&con->swork, process_send_sockets);
  	INIT_WORK(&con->rwork, process_recv_sockets);
  
  	/* Setup action pointers for child sockets */
  	if (con->nodeid) {
  		struct connection *zerocon = __find_con(0);
  
  		con->connect_action = zerocon->connect_action;
  		if (!con->rx_action)
  			con->rx_action = zerocon->rx_action;
  	}
  
  	return con;
  }
  
  /* Loop round all connections */
  static void foreach_conn(void (*conn_func)(struct connection *c))
  {
  	int i;
  	struct hlist_node *n;
  	struct connection *con;
  
  	for (i = 0; i < CONN_HASH_SIZE; i++) {
  		hlist_for_each_entry_safe(con, n, &connection_hash[i], list)
  			conn_func(con);
  	}
  }
  
  static struct connection *nodeid2con(int nodeid, gfp_t allocation)
  {
  	struct connection *con;
  
  	mutex_lock(&connections_lock);
  	con = __nodeid2con(nodeid, allocation);
  	mutex_unlock(&connections_lock);
  
  	return con;
  }
  
  static struct dlm_node_addr *find_node_addr(int nodeid)
  {
  	struct dlm_node_addr *na;
  
  	list_for_each_entry(na, &dlm_node_addrs, list) {
  		if (na->nodeid == nodeid)
  			return na;
  	}
  	return NULL;
  }
  
  static int addr_compare(struct sockaddr_storage *x, struct sockaddr_storage *y)
  {
  	switch (x->ss_family) {
  	case AF_INET: {
  		struct sockaddr_in *sinx = (struct sockaddr_in *)x;
  		struct sockaddr_in *siny = (struct sockaddr_in *)y;
  		if (sinx->sin_addr.s_addr != siny->sin_addr.s_addr)
  			return 0;
  		if (sinx->sin_port != siny->sin_port)
  			return 0;
  		break;
  	}
  	case AF_INET6: {
  		struct sockaddr_in6 *sinx = (struct sockaddr_in6 *)x;
  		struct sockaddr_in6 *siny = (struct sockaddr_in6 *)y;
  		if (!ipv6_addr_equal(&sinx->sin6_addr, &siny->sin6_addr))
  			return 0;
  		if (sinx->sin6_port != siny->sin6_port)
  			return 0;
  		break;
  	}
  	default:
  		return 0;
  	}
  	return 1;
  }
  
  static int nodeid_to_addr(int nodeid, struct sockaddr_storage *sas_out,
  			  struct sockaddr *sa_out, bool try_new_addr)
  {
  	struct sockaddr_storage sas;
  	struct dlm_node_addr *na;
  
  	if (!dlm_local_count)
  		return -1;
  
  	spin_lock(&dlm_node_addrs_spin);
  	na = find_node_addr(nodeid);
  	if (na && na->addr_count) {
  		memcpy(&sas, na->addr[na->curr_addr_index],
  		       sizeof(struct sockaddr_storage));
  
  		if (try_new_addr) {
  			na->curr_addr_index++;
  			if (na->curr_addr_index == na->addr_count)
  				na->curr_addr_index = 0;
  		}
  	}
  	spin_unlock(&dlm_node_addrs_spin);
  
  	if (!na)
  		return -EEXIST;
  
  	if (!na->addr_count)
  		return -ENOENT;
  
  	if (sas_out)
  		memcpy(sas_out, &sas, sizeof(struct sockaddr_storage));
  
  	if (!sa_out)
  		return 0;
  
  	if (dlm_local_addr[0]->ss_family == AF_INET) {
  		struct sockaddr_in *in4  = (struct sockaddr_in *) &sas;
  		struct sockaddr_in *ret4 = (struct sockaddr_in *) sa_out;
  		ret4->sin_addr.s_addr = in4->sin_addr.s_addr;
  	} else {
  		struct sockaddr_in6 *in6  = (struct sockaddr_in6 *) &sas;
  		struct sockaddr_in6 *ret6 = (struct sockaddr_in6 *) sa_out;
  		ret6->sin6_addr = in6->sin6_addr;
  	}
  
  	return 0;
  }
  
  static int addr_to_nodeid(struct sockaddr_storage *addr, int *nodeid)
  {
  	struct dlm_node_addr *na;
  	int rv = -EEXIST;
  	int addr_i;
  
  	spin_lock(&dlm_node_addrs_spin);
  	list_for_each_entry(na, &dlm_node_addrs, list) {
  		if (!na->addr_count)
  			continue;
  
  		for (addr_i = 0; addr_i < na->addr_count; addr_i++) {
  			if (addr_compare(na->addr[addr_i], addr)) {
  				*nodeid = na->nodeid;
  				rv = 0;
  				goto unlock;
  			}
  		}
  	}
  unlock:
  	spin_unlock(&dlm_node_addrs_spin);
  	return rv;
  }
  
  int dlm_lowcomms_addr(int nodeid, struct sockaddr_storage *addr, int len)
  {
  	struct sockaddr_storage *new_addr;
  	struct dlm_node_addr *new_node, *na;
  
  	new_node = kzalloc(sizeof(struct dlm_node_addr), GFP_NOFS);
  	if (!new_node)
  		return -ENOMEM;
  
  	new_addr = kzalloc(sizeof(struct sockaddr_storage), GFP_NOFS);
  	if (!new_addr) {
  		kfree(new_node);
  		return -ENOMEM;
  	}
  
  	memcpy(new_addr, addr, len);
  
  	spin_lock(&dlm_node_addrs_spin);
  	na = find_node_addr(nodeid);
  	if (!na) {
  		new_node->nodeid = nodeid;
  		new_node->addr[0] = new_addr;
  		new_node->addr_count = 1;
  		list_add(&new_node->list, &dlm_node_addrs);
  		spin_unlock(&dlm_node_addrs_spin);
  		return 0;
  	}
  
  	if (na->addr_count >= DLM_MAX_ADDR_COUNT) {
  		spin_unlock(&dlm_node_addrs_spin);
  		kfree(new_addr);
  		kfree(new_node);
  		return -ENOSPC;
  	}
  
  	na->addr[na->addr_count++] = new_addr;
  	spin_unlock(&dlm_node_addrs_spin);
  	kfree(new_node);
  	return 0;
  }
  
  /* Data available on socket or listen socket received a connect */
  static void lowcomms_data_ready(struct sock *sk)
  {
  	struct connection *con;
  
  	read_lock_bh(&sk->sk_callback_lock);
  	con = sock2con(sk);
  	if (con && !test_and_set_bit(CF_READ_PENDING, &con->flags))
  		queue_work(recv_workqueue, &con->rwork);
  	read_unlock_bh(&sk->sk_callback_lock);
  }
  
  static void lowcomms_write_space(struct sock *sk)
  {
  	struct connection *con;
  
  	read_lock_bh(&sk->sk_callback_lock);
  	con = sock2con(sk);
  	if (!con)
  		goto out;
  
  	clear_bit(SOCK_NOSPACE, &con->sock->flags);
  
  	if (test_and_clear_bit(CF_APP_LIMITED, &con->flags)) {
  		con->sock->sk->sk_write_pending--;
  		clear_bit(SOCKWQ_ASYNC_NOSPACE, &con->sock->flags);
  	}
  
  	queue_work(send_workqueue, &con->swork);
  out:
  	read_unlock_bh(&sk->sk_callback_lock);
  }
  
  static inline void lowcomms_connect_sock(struct connection *con)
  {
  	if (test_bit(CF_CLOSE, &con->flags))
  		return;
  	queue_work(send_workqueue, &con->swork);
  	cond_resched();
  }
  
  static void lowcomms_state_change(struct sock *sk)
  {
  	/* SCTP layer is not calling sk_data_ready when the connection
  	 * is done, so we catch the signal through here. Also, it
  	 * doesn't switch socket state when entering shutdown, so we
  	 * skip the write in that case.
  	 */
  	if (sk->sk_shutdown) {
  		if (sk->sk_shutdown == RCV_SHUTDOWN)
  			lowcomms_data_ready(sk);
  	} else if (sk->sk_state == TCP_ESTABLISHED) {
  		lowcomms_write_space(sk);
  	}
  }
  
  int dlm_lowcomms_connect_node(int nodeid)
  {
  	struct connection *con;
  
  	if (nodeid == dlm_our_nodeid())
  		return 0;
  
  	con = nodeid2con(nodeid, GFP_NOFS);
  	if (!con)
  		return -ENOMEM;
  	lowcomms_connect_sock(con);
  	return 0;
  }
  
  static void lowcomms_error_report(struct sock *sk)
  {
  	struct connection *con;
  	struct sockaddr_storage saddr;
  	void (*orig_report)(struct sock *) = NULL;
  
  	read_lock_bh(&sk->sk_callback_lock);
  	con = sock2con(sk);
  	if (con == NULL)
  		goto out;
  
  	orig_report = listen_sock.sk_error_report;
  	if (con->sock == NULL ||
  	    kernel_getpeername(con->sock, (struct sockaddr *)&saddr) < 0) {
  		printk_ratelimited(KERN_ERR "dlm: node %d: socket error "
  				   "sending to node %d, port %d, "
  				   "sk_err=%d/%d\n", dlm_our_nodeid(),
  				   con->nodeid, dlm_config.ci_tcp_port,
  				   sk->sk_err, sk->sk_err_soft);
  	} else if (saddr.ss_family == AF_INET) {
  		struct sockaddr_in *sin4 = (struct sockaddr_in *)&saddr;
  
  		printk_ratelimited(KERN_ERR "dlm: node %d: socket error "
  				   "sending to node %d at %pI4, port %d, "
  				   "sk_err=%d/%d\n", dlm_our_nodeid(),
  				   con->nodeid, &sin4->sin_addr.s_addr,
  				   dlm_config.ci_tcp_port, sk->sk_err,
  				   sk->sk_err_soft);
  	} else {
  		struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)&saddr;
  
  		printk_ratelimited(KERN_ERR "dlm: node %d: socket error "
  				   "sending to node %d at %u.%u.%u.%u, "
  				   "port %d, sk_err=%d/%d\n", dlm_our_nodeid(),
  				   con->nodeid, sin6->sin6_addr.s6_addr32[0],
  				   sin6->sin6_addr.s6_addr32[1],
  				   sin6->sin6_addr.s6_addr32[2],
  				   sin6->sin6_addr.s6_addr32[3],
  				   dlm_config.ci_tcp_port, sk->sk_err,
  				   sk->sk_err_soft);
  	}
  out:
  	read_unlock_bh(&sk->sk_callback_lock);
  	if (orig_report)
  		orig_report(sk);
  }
  
  /* Note: sk_callback_lock must be locked before calling this function. */
  static void save_listen_callbacks(struct socket *sock)
  {
  	struct sock *sk = sock->sk;
  
  	listen_sock.sk_data_ready = sk->sk_data_ready;
  	listen_sock.sk_state_change = sk->sk_state_change;
  	listen_sock.sk_write_space = sk->sk_write_space;
  	listen_sock.sk_error_report = sk->sk_error_report;
  }
  
  static void restore_callbacks(struct socket *sock)
  {
  	struct sock *sk = sock->sk;
  
  	write_lock_bh(&sk->sk_callback_lock);
  	sk->sk_user_data = NULL;
  	sk->sk_data_ready = listen_sock.sk_data_ready;
  	sk->sk_state_change = listen_sock.sk_state_change;
  	sk->sk_write_space = listen_sock.sk_write_space;
  	sk->sk_error_report = listen_sock.sk_error_report;
  	write_unlock_bh(&sk->sk_callback_lock);
  }
  
  /* Make a socket active */
  static void add_sock(struct socket *sock, struct connection *con)
  {
  	struct sock *sk = sock->sk;
  
  	write_lock_bh(&sk->sk_callback_lock);
  	con->sock = sock;
  
  	sk->sk_user_data = con;
  	/* Install a data_ready callback */
  	sk->sk_data_ready = lowcomms_data_ready;
  	sk->sk_write_space = lowcomms_write_space;
  	sk->sk_state_change = lowcomms_state_change;
  	sk->sk_allocation = GFP_NOFS;
  	sk->sk_error_report = lowcomms_error_report;
  	write_unlock_bh(&sk->sk_callback_lock);
  }
  
  /* Add the port number to an IPv6 or 4 sockaddr and return the address
     length */
  static void make_sockaddr(struct sockaddr_storage *saddr, uint16_t port,
  			  int *addr_len)
  {
  	saddr->ss_family =  dlm_local_addr[0]->ss_family;
  	if (saddr->ss_family == AF_INET) {
  		struct sockaddr_in *in4_addr = (struct sockaddr_in *)saddr;
  		in4_addr->sin_port = cpu_to_be16(port);
  		*addr_len = sizeof(struct sockaddr_in);
  		memset(&in4_addr->sin_zero, 0, sizeof(in4_addr->sin_zero));
  	} else {
  		struct sockaddr_in6 *in6_addr = (struct sockaddr_in6 *)saddr;
  		in6_addr->sin6_port = cpu_to_be16(port);
  		*addr_len = sizeof(struct sockaddr_in6);
  	}
  	memset((char *)saddr + *addr_len, 0, sizeof(struct sockaddr_storage) - *addr_len);
  }
  
  /* Close a remote connection and tidy up */
  static void close_connection(struct connection *con, bool and_other,
  			     bool tx, bool rx)
  {
  	bool closing = test_and_set_bit(CF_CLOSING, &con->flags);
  
  	if (tx && !closing && cancel_work_sync(&con->swork)) {
  		log_print("canceled swork for node %d", con->nodeid);
  		clear_bit(CF_WRITE_PENDING, &con->flags);
  	}
  	if (rx && !closing && cancel_work_sync(&con->rwork)) {
  		log_print("canceled rwork for node %d", con->nodeid);
  		clear_bit(CF_READ_PENDING, &con->flags);
  	}
  
  	mutex_lock(&con->sock_mutex);
  	if (con->sock) {
  		restore_callbacks(con->sock);
  		sock_release(con->sock);
  		con->sock = NULL;
  	}
  	if (con->othercon && and_other) {
  		/* Will only re-enter once. */
  		close_connection(con->othercon, false, true, true);
  	}
  	if (con->rx_page) {
  		__free_page(con->rx_page);
  		con->rx_page = NULL;
  	}
  
  	con->retries = 0;
  	mutex_unlock(&con->sock_mutex);
  	clear_bit(CF_CLOSING, &con->flags);
  }
  
  /* Data received from remote end */
  static int receive_from_sock(struct connection *con)
  {
  	int ret = 0;
  	struct msghdr msg = {};
  	struct kvec iov[2];
  	unsigned len;
  	int r;
  	int call_again_soon = 0;
  	int nvec;
  
  	mutex_lock(&con->sock_mutex);
  
  	if (con->sock == NULL) {
  		ret = -EAGAIN;
  		goto out_close;
  	}
  	if (con->nodeid == 0) {
  		ret = -EINVAL;
  		goto out_close;
  	}
  
  	if (con->rx_page == NULL) {
  		/*
  		 * This doesn't need to be atomic, but I think it should
  		 * improve performance if it is.
  		 */
  		con->rx_page = alloc_page(GFP_ATOMIC);
  		if (con->rx_page == NULL)
  			goto out_resched;
  		cbuf_init(&con->cb, PAGE_SIZE);
  	}
  
  	/*
  	 * iov[0] is the bit of the circular buffer between the current end
  	 * point (cb.base + cb.len) and the end of the buffer.
  	 */
  	iov[0].iov_len = con->cb.base - cbuf_data(&con->cb);
  	iov[0].iov_base = page_address(con->rx_page) + cbuf_data(&con->cb);
  	iov[1].iov_len = 0;
  	nvec = 1;
  
  	/*
  	 * iov[1] is the bit of the circular buffer between the start of the
  	 * buffer and the start of the currently used section (cb.base)
  	 */
  	if (cbuf_data(&con->cb) >= con->cb.base) {
  		iov[0].iov_len = PAGE_SIZE - cbuf_data(&con->cb);
  		iov[1].iov_len = con->cb.base;
  		iov[1].iov_base = page_address(con->rx_page);
  		nvec = 2;
  	}
  	len = iov[0].iov_len + iov[1].iov_len;
  	iov_iter_kvec(&msg.msg_iter, READ, iov, nvec, len);
  
  	r = ret = sock_recvmsg(con->sock, &msg, MSG_DONTWAIT | MSG_NOSIGNAL);
  	if (ret <= 0)
  		goto out_close;
  	else if (ret == len)
  		call_again_soon = 1;
  
  	cbuf_add(&con->cb, ret);
  	ret = dlm_process_incoming_buffer(con->nodeid,
  					  page_address(con->rx_page),
  					  con->cb.base, con->cb.len,
  					  PAGE_SIZE);
  	if (ret == -EBADMSG) {
  		log_print("lowcomms: addr=%p, base=%u, len=%u, read=%d",
  			  page_address(con->rx_page), con->cb.base,
  			  con->cb.len, r);
  	}
  	if (ret < 0)
  		goto out_close;
  	cbuf_eat(&con->cb, ret);
  
  	if (cbuf_empty(&con->cb) && !call_again_soon) {
  		__free_page(con->rx_page);
  		con->rx_page = NULL;
  	}
  
  	if (call_again_soon)
  		goto out_resched;
  	mutex_unlock(&con->sock_mutex);
  	return 0;
  
  out_resched:
  	if (!test_and_set_bit(CF_READ_PENDING, &con->flags))
  		queue_work(recv_workqueue, &con->rwork);
  	mutex_unlock(&con->sock_mutex);
  	return -EAGAIN;
  
  out_close:
  	mutex_unlock(&con->sock_mutex);
  	if (ret != -EAGAIN) {
  		close_connection(con, true, true, false);
  		/* Reconnect when there is something to send */
  	}
  	/* Don't return success if we really got EOF */
  	if (ret == 0)
  		ret = -EAGAIN;
  
  	return ret;
  }
  
  /* Listening socket is busy, accept a connection */
  static int accept_from_sock(struct connection *con)
  {
  	int result;
  	struct sockaddr_storage peeraddr;
  	struct socket *newsock;
  	int len;
  	int nodeid;
  	struct connection *newcon;
  	struct connection *addcon;
  
  	mutex_lock(&connections_lock);
  	if (!dlm_allow_conn) {
  		mutex_unlock(&connections_lock);
  		return -1;
  	}
  	mutex_unlock(&connections_lock);
  
  	mutex_lock_nested(&con->sock_mutex, 0);
  
  	if (!con->sock) {
  		mutex_unlock(&con->sock_mutex);
  		return -ENOTCONN;
  	}
  
  	result = kernel_accept(con->sock, &newsock, O_NONBLOCK);
  	if (result < 0)
  		goto accept_err;
  
  	/* Get the connected socket's peer */
  	memset(&peeraddr, 0, sizeof(peeraddr));
  	len = newsock->ops->getname(newsock, (struct sockaddr *)&peeraddr, 2);
  	if (len < 0) {
  		result = -ECONNABORTED;
  		goto accept_err;
  	}
  
  	/* Get the new node's NODEID */
  	make_sockaddr(&peeraddr, 0, &len);
  	if (addr_to_nodeid(&peeraddr, &nodeid)) {
  		unsigned char *b=(unsigned char *)&peeraddr;
  		log_print("connect from non cluster node");
  		print_hex_dump_bytes("ss: ", DUMP_PREFIX_NONE, 
  				     b, sizeof(struct sockaddr_storage));
  		sock_release(newsock);
  		mutex_unlock(&con->sock_mutex);
  		return -1;
  	}
  
  	log_print("got connection from %d", nodeid);
  
  	/*  Check to see if we already have a connection to this node. This
  	 *  could happen if the two nodes initiate a connection at roughly
  	 *  the same time and the connections cross on the wire.
  	 *  In this case we store the incoming one in "othercon"
  	 */
  	newcon = nodeid2con(nodeid, GFP_NOFS);
  	if (!newcon) {
  		result = -ENOMEM;
  		goto accept_err;
  	}
  	mutex_lock_nested(&newcon->sock_mutex, 1);
  	if (newcon->sock) {
  		struct connection *othercon = newcon->othercon;
  
  		if (!othercon) {
  			othercon = kmem_cache_zalloc(con_cache, GFP_NOFS);
  			if (!othercon) {
  				log_print("failed to allocate incoming socket");
  				mutex_unlock(&newcon->sock_mutex);
  				result = -ENOMEM;
  				goto accept_err;
  			}
  			othercon->nodeid = nodeid;
  			othercon->rx_action = receive_from_sock;
  			mutex_init(&othercon->sock_mutex);
  			INIT_LIST_HEAD(&othercon->writequeue);
  			spin_lock_init(&othercon->writequeue_lock);
  			INIT_WORK(&othercon->swork, process_send_sockets);
  			INIT_WORK(&othercon->rwork, process_recv_sockets);
  			set_bit(CF_IS_OTHERCON, &othercon->flags);
  		}
  		mutex_lock_nested(&othercon->sock_mutex, 2);
  		if (!othercon->sock) {
  			newcon->othercon = othercon;
  			add_sock(newsock, othercon);
  			addcon = othercon;
  			mutex_unlock(&othercon->sock_mutex);
  		}
  		else {
  			printk("Extra connection from node %d attempted\n", nodeid);
  			result = -EAGAIN;
  			mutex_unlock(&othercon->sock_mutex);
  			mutex_unlock(&newcon->sock_mutex);
  			goto accept_err;
  		}
  	}
  	else {
  		newcon->rx_action = receive_from_sock;
  		/* accept copies the sk after we've saved the callbacks, so we
  		   don't want to save them a second time or comm errors will
  		   result in calling sk_error_report recursively. */
  		add_sock(newsock, newcon);
  		addcon = newcon;
  	}
  
  	mutex_unlock(&newcon->sock_mutex);
  
  	/*
  	 * Add it to the active queue in case we got data
  	 * between processing the accept adding the socket
  	 * to the read_sockets list
  	 */
  	if (!test_and_set_bit(CF_READ_PENDING, &addcon->flags))
  		queue_work(recv_workqueue, &addcon->rwork);
  	mutex_unlock(&con->sock_mutex);
  
  	return 0;
  
  accept_err:
  	mutex_unlock(&con->sock_mutex);
  	if (newsock)
  		sock_release(newsock);
  
  	if (result != -EAGAIN)
  		log_print("error accepting connection from node: %d", result);
  	return result;
  }
  
  static void free_entry(struct writequeue_entry *e)
  {
  	__free_page(e->page);
  	kfree(e);
  }
  
  /*
   * writequeue_entry_complete - try to delete and free write queue entry
   * @e: write queue entry to try to delete
   * @completed: bytes completed
   *
   * writequeue_lock must be held.
   */
  static void writequeue_entry_complete(struct writequeue_entry *e, int completed)
  {
  	e->offset += completed;
  	e->len -= completed;
  
  	if (e->len == 0 && e->users == 0) {
  		list_del(&e->list);
  		free_entry(e);
  	}
  }
  
  /*
   * sctp_bind_addrs - bind a SCTP socket to all our addresses
   */
  static int sctp_bind_addrs(struct connection *con, uint16_t port)
  {
  	struct sockaddr_storage localaddr;
  	struct sockaddr *addr = (struct sockaddr *)&localaddr;
  	int i, addr_len, result = 0;
  
  	for (i = 0; i < dlm_local_count; i++) {
  		memcpy(&localaddr, dlm_local_addr[i], sizeof(localaddr));
  		make_sockaddr(&localaddr, port, &addr_len);
  
  		if (!i)
  			result = kernel_bind(con->sock, addr, addr_len);
  		else
  			result = sock_bind_add(con->sock->sk, addr, addr_len);
  
  		if (result < 0) {
  			log_print("Can't bind to %d addr number %d, %d.\n",
  				  port, i + 1, result);
  			break;
  		}
  	}
  	return result;
  }
  
  /* Initiate an SCTP association.
     This is a special case of send_to_sock() in that we don't yet have a
     peeled-off socket for this association, so we use the listening socket
     and add the primary IP address of the remote node.
   */
  static void sctp_connect_to_sock(struct connection *con)
  {
  	struct sockaddr_storage daddr;
  	int result;
  	int addr_len;
  	struct socket *sock;
  
  	if (con->nodeid == 0) {
  		log_print("attempt to connect sock 0 foiled");
  		return;
  	}
  
  	mutex_lock(&con->sock_mutex);
  
  	/* Some odd races can cause double-connects, ignore them */
  	if (con->retries++ > MAX_CONNECT_RETRIES)
  		goto out;
  
  	if (con->sock) {
  		log_print("node %d already connected.", con->nodeid);
  		goto out;
  	}
  
  	memset(&daddr, 0, sizeof(daddr));
  	result = nodeid_to_addr(con->nodeid, &daddr, NULL, true);
  	if (result < 0) {
  		log_print("no address for nodeid %d", con->nodeid);
  		goto out;
  	}
  
  	/* Create a socket to communicate with */
  	result = sock_create_kern(&init_net, dlm_local_addr[0]->ss_family,
  				  SOCK_STREAM, IPPROTO_SCTP, &sock);
  	if (result < 0)
  		goto socket_err;
  
  	con->rx_action = receive_from_sock;
  	con->connect_action = sctp_connect_to_sock;
  	add_sock(sock, con);
  
  	/* Bind to all addresses. */
  	if (sctp_bind_addrs(con, 0))
  		goto bind_err;
  
  	make_sockaddr(&daddr, dlm_config.ci_tcp_port, &addr_len);
  
  	log_print("connecting to %d", con->nodeid);
  
  	/* Turn off Nagle's algorithm */
  	sctp_sock_set_nodelay(sock->sk);
  
  	/*
  	 * Make sock->ops->connect() function return in specified time,
  	 * since O_NONBLOCK argument in connect() function does not work here,
  	 * then, we should restore the default value of this attribute.
  	 */
  	sock_set_sndtimeo(sock->sk, 5);
  	result = sock->ops->connect(sock, (struct sockaddr *)&daddr, addr_len,
  				   0);
  	sock_set_sndtimeo(sock->sk, 0);
  
  	if (result == -EINPROGRESS)
  		result = 0;
  	if (result == 0)
  		goto out;
  
  bind_err:
  	con->sock = NULL;
  	sock_release(sock);
  
  socket_err:
  	/*
  	 * Some errors are fatal and this list might need adjusting. For other
  	 * errors we try again until the max number of retries is reached.
  	 */
  	if (result != -EHOSTUNREACH &&
  	    result != -ENETUNREACH &&
  	    result != -ENETDOWN &&
  	    result != -EINVAL &&
  	    result != -EPROTONOSUPPORT) {
  		log_print("connect %d try %d error %d", con->nodeid,
  			  con->retries, result);
  		mutex_unlock(&con->sock_mutex);
  		msleep(1000);
  		lowcomms_connect_sock(con);
  		return;
  	}
  
  out:
  	mutex_unlock(&con->sock_mutex);
  }
  
  /* Connect a new socket to its peer */
  static void tcp_connect_to_sock(struct connection *con)
  {
  	struct sockaddr_storage saddr, src_addr;
  	int addr_len;
  	struct socket *sock = NULL;
  	int result;
  
  	if (con->nodeid == 0) {
  		log_print("attempt to connect sock 0 foiled");
  		return;
  	}
  
  	mutex_lock(&con->sock_mutex);
  	if (con->retries++ > MAX_CONNECT_RETRIES)
  		goto out;
  
  	/* Some odd races can cause double-connects, ignore them */
  	if (con->sock)
  		goto out;
  
  	/* Create a socket to communicate with */
  	result = sock_create_kern(&init_net, dlm_local_addr[0]->ss_family,
  				  SOCK_STREAM, IPPROTO_TCP, &sock);
  	if (result < 0)
  		goto out_err;
  
  	memset(&saddr, 0, sizeof(saddr));
  	result = nodeid_to_addr(con->nodeid, &saddr, NULL, false);
  	if (result < 0) {
  		log_print("no address for nodeid %d", con->nodeid);
  		goto out_err;
  	}
  
  	con->rx_action = receive_from_sock;
  	con->connect_action = tcp_connect_to_sock;
  	add_sock(sock, con);
  
  	/* Bind to our cluster-known address connecting to avoid
  	   routing problems */
  	memcpy(&src_addr, dlm_local_addr[0], sizeof(src_addr));
  	make_sockaddr(&src_addr, 0, &addr_len);
  	result = sock->ops->bind(sock, (struct sockaddr *) &src_addr,
  				 addr_len);
  	if (result < 0) {
  		log_print("could not bind for connect: %d", result);
  		/* This *may* not indicate a critical error */
  	}
  
  	make_sockaddr(&saddr, dlm_config.ci_tcp_port, &addr_len);
  
  	log_print("connecting to %d", con->nodeid);
  
  	/* Turn off Nagle's algorithm */
  	tcp_sock_set_nodelay(sock->sk);
  
  	result = sock->ops->connect(sock, (struct sockaddr *)&saddr, addr_len,
  				   O_NONBLOCK);
  	if (result == -EINPROGRESS)
  		result = 0;
  	if (result == 0)
  		goto out;
  
  out_err:
  	if (con->sock) {
  		sock_release(con->sock);
  		con->sock = NULL;
  	} else if (sock) {
  		sock_release(sock);
  	}
  	/*
  	 * Some errors are fatal and this list might need adjusting. For other
  	 * errors we try again until the max number of retries is reached.
  	 */
  	if (result != -EHOSTUNREACH &&
  	    result != -ENETUNREACH &&
  	    result != -ENETDOWN && 
  	    result != -EINVAL &&
  	    result != -EPROTONOSUPPORT) {
  		log_print("connect %d try %d error %d", con->nodeid,
  			  con->retries, result);
  		mutex_unlock(&con->sock_mutex);
  		msleep(1000);
  		lowcomms_connect_sock(con);
  		return;
  	}
  out:
  	mutex_unlock(&con->sock_mutex);
  	return;
  }
  
  static struct socket *tcp_create_listen_sock(struct connection *con,
  					     struct sockaddr_storage *saddr)
  {
  	struct socket *sock = NULL;
  	int result = 0;
  	int addr_len;
  
  	if (dlm_local_addr[0]->ss_family == AF_INET)
  		addr_len = sizeof(struct sockaddr_in);
  	else
  		addr_len = sizeof(struct sockaddr_in6);
  
  	/* Create a socket to communicate with */
  	result = sock_create_kern(&init_net, dlm_local_addr[0]->ss_family,
  				  SOCK_STREAM, IPPROTO_TCP, &sock);
  	if (result < 0) {
  		log_print("Can't create listening comms socket");
  		goto create_out;
  	}
  
  	/* Turn off Nagle's algorithm */
  	tcp_sock_set_nodelay(sock->sk);
  
  	sock_set_reuseaddr(sock->sk);
  
  	write_lock_bh(&sock->sk->sk_callback_lock);
  	sock->sk->sk_user_data = con;
  	save_listen_callbacks(sock);
  	con->rx_action = accept_from_sock;
  	con->connect_action = tcp_connect_to_sock;
  	write_unlock_bh(&sock->sk->sk_callback_lock);
  
  	/* Bind to our port */
  	make_sockaddr(saddr, dlm_config.ci_tcp_port, &addr_len);
  	result = sock->ops->bind(sock, (struct sockaddr *) saddr, addr_len);
  	if (result < 0) {
  		log_print("Can't bind to port %d", dlm_config.ci_tcp_port);
  		sock_release(sock);
  		sock = NULL;
  		con->sock = NULL;
  		goto create_out;
  	}
  	sock_set_keepalive(sock->sk);
  
  	result = sock->ops->listen(sock, 5);
  	if (result < 0) {
  		log_print("Can't listen on port %d", dlm_config.ci_tcp_port);
  		sock_release(sock);
  		sock = NULL;
  		goto create_out;
  	}
  
  create_out:
  	return sock;
  }
  
  /* Get local addresses */
  static void init_local(void)
  {
  	struct sockaddr_storage sas, *addr;
  	int i;
  
  	dlm_local_count = 0;
  	for (i = 0; i < DLM_MAX_ADDR_COUNT; i++) {
  		if (dlm_our_addr(&sas, i))
  			break;
  
  		addr = kmemdup(&sas, sizeof(*addr), GFP_NOFS);
  		if (!addr)
  			break;
  		dlm_local_addr[dlm_local_count++] = addr;
  	}
  }
  
  /* Initialise SCTP socket and bind to all interfaces */
  static int sctp_listen_for_all(void)
  {
  	struct socket *sock = NULL;
  	int result = -EINVAL;
  	struct connection *con = nodeid2con(0, GFP_NOFS);
  
  	if (!con)
  		return -ENOMEM;
  
  	log_print("Using SCTP for communications");
  
  	result = sock_create_kern(&init_net, dlm_local_addr[0]->ss_family,
  				  SOCK_STREAM, IPPROTO_SCTP, &sock);
  	if (result < 0) {
  		log_print("Can't create comms socket, check SCTP is loaded");
  		goto out;
  	}
  
  	sock_set_rcvbuf(sock->sk, NEEDED_RMEM);
  	sctp_sock_set_nodelay(sock->sk);
  
  	write_lock_bh(&sock->sk->sk_callback_lock);
  	/* Init con struct */
  	sock->sk->sk_user_data = con;
  	save_listen_callbacks(sock);
  	con->sock = sock;
  	con->sock->sk->sk_data_ready = lowcomms_data_ready;
  	con->rx_action = accept_from_sock;
  	con->connect_action = sctp_connect_to_sock;
  
  	write_unlock_bh(&sock->sk->sk_callback_lock);
  
  	/* Bind to all addresses. */
  	if (sctp_bind_addrs(con, dlm_config.ci_tcp_port))
  		goto create_delsock;
  
  	result = sock->ops->listen(sock, 5);
  	if (result < 0) {
  		log_print("Can't set socket listening");
  		goto create_delsock;
  	}
  
  	return 0;
  
  create_delsock:
  	sock_release(sock);
  	con->sock = NULL;
  out:
  	return result;
  }
  
  static int tcp_listen_for_all(void)
  {
  	struct socket *sock = NULL;
  	struct connection *con = nodeid2con(0, GFP_NOFS);
  	int result = -EINVAL;
  
  	if (!con)
  		return -ENOMEM;
  
  	/* We don't support multi-homed hosts */
  	if (dlm_local_addr[1] != NULL) {
  		log_print("TCP protocol can't handle multi-homed hosts, "
  			  "try SCTP");
  		return -EINVAL;
  	}
  
  	log_print("Using TCP for communications");
  
  	sock = tcp_create_listen_sock(con, dlm_local_addr[0]);
  	if (sock) {
  		add_sock(sock, con);
  		result = 0;
  	}
  	else {
  		result = -EADDRINUSE;
  	}
  
  	return result;
  }
  
  
  
  static struct writequeue_entry *new_writequeue_entry(struct connection *con,
  						     gfp_t allocation)
  {
  	struct writequeue_entry *entry;
  
  	entry = kmalloc(sizeof(struct writequeue_entry), allocation);
  	if (!entry)
  		return NULL;
  
  	entry->page = alloc_page(allocation);
  	if (!entry->page) {
  		kfree(entry);
  		return NULL;
  	}
  
  	entry->offset = 0;
  	entry->len = 0;
  	entry->end = 0;
  	entry->users = 0;
  	entry->con = con;
  
  	return entry;
  }
  
  void *dlm_lowcomms_get_buffer(int nodeid, int len, gfp_t allocation, char **ppc)
  {
  	struct connection *con;
  	struct writequeue_entry *e;
  	int offset = 0;
  
  	con = nodeid2con(nodeid, allocation);
  	if (!con)
  		return NULL;
  
  	spin_lock(&con->writequeue_lock);
  	e = list_entry(con->writequeue.prev, struct writequeue_entry, list);
  	if ((&e->list == &con->writequeue) ||
  	    (PAGE_SIZE - e->end < len)) {
  		e = NULL;
  	} else {
  		offset = e->end;
  		e->end += len;
  		e->users++;
  	}
  	spin_unlock(&con->writequeue_lock);
  
  	if (e) {
  	got_one:
  		*ppc = page_address(e->page) + offset;
  		return e;
  	}
  
  	e = new_writequeue_entry(con, allocation);
  	if (e) {
  		spin_lock(&con->writequeue_lock);
  		offset = e->end;
  		e->end += len;
  		e->users++;
  		list_add_tail(&e->list, &con->writequeue);
  		spin_unlock(&con->writequeue_lock);
  		goto got_one;
  	}
  	return NULL;
  }
  
  void dlm_lowcomms_commit_buffer(void *mh)
  {
  	struct writequeue_entry *e = (struct writequeue_entry *)mh;
  	struct connection *con = e->con;
  	int users;
  
  	spin_lock(&con->writequeue_lock);
  	users = --e->users;
  	if (users)
  		goto out;
  	e->len = e->end - e->offset;
  	spin_unlock(&con->writequeue_lock);
  
  	queue_work(send_workqueue, &con->swork);
  	return;
  
  out:
  	spin_unlock(&con->writequeue_lock);
  	return;
  }
  
  /* Send a message */
  static void send_to_sock(struct connection *con)
  {
  	int ret = 0;
  	const int msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL;
  	struct writequeue_entry *e;
  	int len, offset;
  	int count = 0;
  
  	mutex_lock(&con->sock_mutex);
  	if (con->sock == NULL)
  		goto out_connect;
  
  	spin_lock(&con->writequeue_lock);
  	for (;;) {
  		e = list_entry(con->writequeue.next, struct writequeue_entry,
  			       list);
  		if ((struct list_head *) e == &con->writequeue)
  			break;
  
  		len = e->len;
  		offset = e->offset;
  		BUG_ON(len == 0 && e->users == 0);
  		spin_unlock(&con->writequeue_lock);
  
  		ret = 0;
  		if (len) {
  			ret = kernel_sendpage(con->sock, e->page, offset, len,
  					      msg_flags);
  			if (ret == -EAGAIN || ret == 0) {
  				if (ret == -EAGAIN &&
  				    test_bit(SOCKWQ_ASYNC_NOSPACE, &con->sock->flags) &&
  				    !test_and_set_bit(CF_APP_LIMITED, &con->flags)) {
  					/* Notify TCP that we're limited by the
  					 * application window size.
  					 */
  					set_bit(SOCK_NOSPACE, &con->sock->flags);
  					con->sock->sk->sk_write_pending++;
  				}
  				cond_resched();
  				goto out;
  			} else if (ret < 0)
  				goto send_error;
  		}
  
  		/* Don't starve people filling buffers */
  		if (++count >= MAX_SEND_MSG_COUNT) {
  			cond_resched();
  			count = 0;
  		}
  
  		spin_lock(&con->writequeue_lock);
  		writequeue_entry_complete(e, ret);
  	}
  	spin_unlock(&con->writequeue_lock);
  out:
  	mutex_unlock(&con->sock_mutex);
  	return;
  
  send_error:
  	mutex_unlock(&con->sock_mutex);
  	close_connection(con, true, false, true);
  	/* Requeue the send work. When the work daemon runs again, it will try
  	   a new connection, then call this function again. */
  	queue_work(send_workqueue, &con->swork);
  	return;
  
  out_connect:
  	mutex_unlock(&con->sock_mutex);
  	queue_work(send_workqueue, &con->swork);
  	cond_resched();
  }
  
  static void clean_one_writequeue(struct connection *con)
  {
  	struct writequeue_entry *e, *safe;
  
  	spin_lock(&con->writequeue_lock);
  	list_for_each_entry_safe(e, safe, &con->writequeue, list) {
  		list_del(&e->list);
  		free_entry(e);
  	}
  	spin_unlock(&con->writequeue_lock);
  }
  
  /* Called from recovery when it knows that a node has
     left the cluster */
  int dlm_lowcomms_close(int nodeid)
  {
  	struct connection *con;
  	struct dlm_node_addr *na;
  
  	log_print("closing connection to node %d", nodeid);
  	con = nodeid2con(nodeid, 0);
  	if (con) {
  		set_bit(CF_CLOSE, &con->flags);
  		close_connection(con, true, true, true);
  		clean_one_writequeue(con);
  	}
  
  	spin_lock(&dlm_node_addrs_spin);
  	na = find_node_addr(nodeid);
  	if (na) {
  		list_del(&na->list);
  		while (na->addr_count--)
  			kfree(na->addr[na->addr_count]);
  		kfree(na);
  	}
  	spin_unlock(&dlm_node_addrs_spin);
  
  	return 0;
  }
  
  /* Receive workqueue function */
  static void process_recv_sockets(struct work_struct *work)
  {
  	struct connection *con = container_of(work, struct connection, rwork);
  	int err;
  
  	clear_bit(CF_READ_PENDING, &con->flags);
  	do {
  		err = con->rx_action(con);
  	} while (!err);
  }
  
  /* Send workqueue function */
  static void process_send_sockets(struct work_struct *work)
  {
  	struct connection *con = container_of(work, struct connection, swork);
  
  	clear_bit(CF_WRITE_PENDING, &con->flags);
  	if (con->sock == NULL) /* not mutex protected so check it inside too */
  		con->connect_action(con);
  	if (!list_empty(&con->writequeue))
  		send_to_sock(con);
  }
  
  
  /* Discard all entries on the write queues */
  static void clean_writequeues(void)
  {
  	foreach_conn(clean_one_writequeue);
  }
  
  static void work_stop(void)
  {
  	if (recv_workqueue)
  		destroy_workqueue(recv_workqueue);
  	if (send_workqueue)
  		destroy_workqueue(send_workqueue);
  }
  
  static int work_start(void)
  {
  	recv_workqueue = alloc_workqueue("dlm_recv",
  					 WQ_UNBOUND | WQ_MEM_RECLAIM, 1);
  	if (!recv_workqueue) {
  		log_print("can't start dlm_recv");
  		return -ENOMEM;
  	}
  
  	send_workqueue = alloc_workqueue("dlm_send",
  					 WQ_UNBOUND | WQ_MEM_RECLAIM, 1);
  	if (!send_workqueue) {
  		log_print("can't start dlm_send");
  		destroy_workqueue(recv_workqueue);
  		return -ENOMEM;
  	}
  
  	return 0;
  }
  
  static void _stop_conn(struct connection *con, bool and_other)
  {
  	mutex_lock(&con->sock_mutex);
  	set_bit(CF_CLOSE, &con->flags);
  	set_bit(CF_READ_PENDING, &con->flags);
  	set_bit(CF_WRITE_PENDING, &con->flags);
  	if (con->sock && con->sock->sk) {
  		write_lock_bh(&con->sock->sk->sk_callback_lock);
  		con->sock->sk->sk_user_data = NULL;
  		write_unlock_bh(&con->sock->sk->sk_callback_lock);
  	}
  	if (con->othercon && and_other)
  		_stop_conn(con->othercon, false);
  	mutex_unlock(&con->sock_mutex);
  }
  
  static void stop_conn(struct connection *con)
  {
  	_stop_conn(con, true);
  }
  
  static void free_conn(struct connection *con)
  {
  	close_connection(con, true, true, true);
  	if (con->othercon)
  		kmem_cache_free(con_cache, con->othercon);
  	hlist_del(&con->list);
  	kmem_cache_free(con_cache, con);
  }
  
  static void work_flush(void)
  {
  	int ok;
  	int i;
  	struct hlist_node *n;
  	struct connection *con;
  
  	if (recv_workqueue)
  		flush_workqueue(recv_workqueue);
  	if (send_workqueue)
  		flush_workqueue(send_workqueue);
  	do {
  		ok = 1;
  		foreach_conn(stop_conn);
  		if (recv_workqueue)
  			flush_workqueue(recv_workqueue);
  		if (send_workqueue)
  			flush_workqueue(send_workqueue);
  		for (i = 0; i < CONN_HASH_SIZE && ok; i++) {
  			hlist_for_each_entry_safe(con, n,
  						  &connection_hash[i], list) {
  				ok &= test_bit(CF_READ_PENDING, &con->flags);
  				ok &= test_bit(CF_WRITE_PENDING, &con->flags);
  				if (con->othercon) {
  					ok &= test_bit(CF_READ_PENDING,
  						       &con->othercon->flags);
  					ok &= test_bit(CF_WRITE_PENDING,
  						       &con->othercon->flags);
  				}
  			}
  		}
  	} while (!ok);
  }
  
  void dlm_lowcomms_stop(void)
  {
  	/* Set all the flags to prevent any
  	   socket activity.
  	*/
  	mutex_lock(&connections_lock);
  	dlm_allow_conn = 0;
  	mutex_unlock(&connections_lock);
  	work_flush();
  	clean_writequeues();
  	foreach_conn(free_conn);
  	work_stop();
  
  	kmem_cache_destroy(con_cache);
  }
  
  int dlm_lowcomms_start(void)
  {
  	int error = -EINVAL;
  	struct connection *con;
  	int i;
  
  	for (i = 0; i < CONN_HASH_SIZE; i++)
  		INIT_HLIST_HEAD(&connection_hash[i]);
  
  	init_local();
  	if (!dlm_local_count) {
  		error = -ENOTCONN;
  		log_print("no local IP address has been set");
  		goto fail;
  	}
  
  	error = -ENOMEM;
  	con_cache = kmem_cache_create("dlm_conn", sizeof(struct connection),
  				      __alignof__(struct connection), 0,
  				      NULL);
  	if (!con_cache)
  		goto fail;
  
  	error = work_start();
  	if (error)
  		goto fail_destroy;
  
  	dlm_allow_conn = 1;
  
  	/* Start listening */
  	if (dlm_config.ci_protocol == 0)
  		error = tcp_listen_for_all();
  	else
  		error = sctp_listen_for_all();
  	if (error)
  		goto fail_unlisten;
  
  	return 0;
  
  fail_unlisten:
  	dlm_allow_conn = 0;
  	con = nodeid2con(0,0);
  	if (con) {
  		close_connection(con, false, true, true);
  		kmem_cache_free(con_cache, con);
  	}
  fail_destroy:
  	kmem_cache_destroy(con_cache);
  fail:
  	return error;
  }
  
  void dlm_lowcomms_exit(void)
  {
  	struct dlm_node_addr *na, *safe;
  
  	spin_lock(&dlm_node_addrs_spin);
  	list_for_each_entry_safe(na, safe, &dlm_node_addrs, list) {
  		list_del(&na->list);
  		while (na->addr_count--)
  			kfree(na->addr[na->addr_count]);
  		kfree(na);
  	}
  	spin_unlock(&dlm_node_addrs_spin);
  }
  