[DLM] Consolidate transport protocols

This patch consolidates the TCP & SCTP protocols for the DLM into a single file
and makes it switchable at run-time (well, at least before the DLM actually
starts up!)

For RHEL5 this patch requires Neil Horman's patch that expands the in-kernel
socket API but that has already been twice ACKed so it should be OK.

The patch adds a new lowcomms.c file that replaces the existing lowcomms-sctp.c
& lowcomms-tcp.c files.

Signed-off-By: Patrick Caulfield <pcaulfie@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 1468 insertions, 0 deletions

diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
new file mode 100644
index 000000000000..76399b7819b4
--- /dev/null
+++ b/fs/dlm/lowcomms.c
@@ -0,0 +1,1468 @@
+/******************************************************************************
+*******************************************************************************
+**
+**  Copyright (C) Sistina Software, Inc.  1997-2003  All rights reserved.
+**  Copyright (C) 2004-2007 Red Hat, Inc.  All rights reserved.
+**
+**  This copyrighted material is made available to anyone wishing to use,
+**  modify, copy, or redistribute it subject to the terms and conditions
+**  of the GNU General Public License v.2.
+**
+*******************************************************************************
+******************************************************************************/
+
+/*
+ * 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 it's
+ * 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 wither 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 shouldbe 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/idr.h>
+#include <linux/file.h>
+#include <linux/sctp.h>
+#include <net/sctp/user.h>
+
+#include "dlm_internal.h"
+#include "lowcomms.h"
+#include "midcomms.h"
+#include "config.h"
+
+#define NEEDED_RMEM (4*1024*1024)
+
+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_CONNECT_PENDING 3
+#define CF_INIT_PENDING 4
+#define CF_IS_OTHERCON 5
+	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
+	int sctp_assoc;
+	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;
+};
+
+static struct sockaddr_storage *dlm_local_addr[DLM_MAX_ADDR_COUNT];
+static int dlm_local_count;
+
+/* Work queues */
+static struct workqueue_struct *recv_workqueue;
+static struct workqueue_struct *send_workqueue;
+
+static DEFINE_IDR(connections_idr);
+static DECLARE_MUTEX(connections_lock);
+static int max_nodeid;
+static struct kmem_cache *con_cache;
+
+static void process_recv_sockets(struct work_struct *work);
+static void process_send_sockets(struct work_struct *work);
+
+/*
+ * 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;
+	int n;
+
+	con = idr_find(&connections_idr, nodeid);
+	if (con || !alloc)
+		return con;
+
+	r = idr_pre_get(&connections_idr, alloc);
+	if (!r)
+		return NULL;
+
+	con = kmem_cache_zalloc(con_cache, alloc);
+	if (!con)
+		return NULL;
+
+	r = idr_get_new_above(&connections_idr, con, nodeid, &n);
+	if (r) {
+		kmem_cache_free(con_cache, con);
+		return NULL;
+	}
+
+	if (n != nodeid) {
+		idr_remove(&connections_idr, n);
+		kmem_cache_free(con_cache, con);
+		return NULL;
+	}
+
+	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 = idr_find(&connections_idr, 0);
+
+		con->connect_action = zerocon->connect_action;
+		if (!con->rx_action)
+			con->rx_action = zerocon->rx_action;
+	}
+
+	if (nodeid > max_nodeid)
+		max_nodeid = nodeid;
+
+	return con;
+}
+
+static struct connection *nodeid2con(int nodeid, gfp_t allocation)
+{
+	struct connection *con;
+
+	down(&connections_lock);
+	con = __nodeid2con(nodeid, allocation);
+	up(&connections_lock);
+
+	return con;
+}
+
+/* This is a bit drastic, but only called when things go wrong */
+static struct connection *assoc2con(int assoc_id)
+{
+	int i;
+	struct connection *con;
+
+	down(&connections_lock);
+	for (i=0; i<max_nodeid; i++) {
+		con = __nodeid2con(i, 0);
+		if (con && con->sctp_assoc == assoc_id) {
+			up(&connections_lock);
+			return con;
+		}
+	}
+	up(&connections_lock);
+	return NULL;
+}
+
+static int nodeid_to_addr(int nodeid, struct sockaddr *retaddr)
+{
+	struct sockaddr_storage addr;
+	int error;
+
+	if (!dlm_local_count)
+		return -1;
+
+	error = dlm_nodeid_to_addr(nodeid, &addr);
+	if (error)
+		return error;
+
+	if (dlm_local_addr[0]->ss_family == AF_INET) {
+		struct sockaddr_in *in4  = (struct sockaddr_in *) &addr;
+		struct sockaddr_in *ret4 = (struct sockaddr_in *) retaddr;
+		ret4->sin_addr.s_addr = in4->sin_addr.s_addr;
+	} else {
+		struct sockaddr_in6 *in6  = (struct sockaddr_in6 *) &addr;
+		struct sockaddr_in6 *ret6 = (struct sockaddr_in6 *) retaddr;
+		memcpy(&ret6->sin6_addr, &in6->sin6_addr,
+		       sizeof(in6->sin6_addr));
+	}
+
+	return 0;
+}
+
+/* Data available on socket or listen socket received a connect */
+static void lowcomms_data_ready(struct sock *sk, int count_unused)
+{
+	struct connection *con = sock2con(sk);
+	if (!test_and_set_bit(CF_READ_PENDING, &con->flags))
+		queue_work(recv_workqueue, &con->rwork);
+}
+
+static void lowcomms_write_space(struct sock *sk)
+{
+	struct connection *con = sock2con(sk);
+
+	if (!test_and_set_bit(CF_WRITE_PENDING, &con->flags))
+		queue_work(send_workqueue, &con->swork);
+}
+
+static inline void lowcomms_connect_sock(struct connection *con)
+{
+	if (!test_and_set_bit(CF_CONNECT_PENDING, &con->flags))
+		queue_work(send_workqueue, &con->swork);
+}
+
+static void lowcomms_state_change(struct sock *sk)
+{
+	if (sk->sk_state == TCP_ESTABLISHED)
+		lowcomms_write_space(sk);
+}
+
+/* Make a socket active */
+static int add_sock(struct socket *sock, struct connection *con)
+{
+	con->sock = sock;
+
+	/* Install a data_ready callback */
+	con->sock->sk->sk_data_ready = lowcomms_data_ready;
+	con->sock->sk->sk_write_space = lowcomms_write_space;
+	con->sock->sk->sk_state_change = lowcomms_state_change;
+	con->sock->sk->sk_user_data = con;
+	return 0;
+}
+
+/* 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);
+	}
+}
+
+/* Close a remote connection and tidy up */
+static void close_connection(struct connection *con, bool and_other)
+{
+	mutex_lock(&con->sock_mutex);
+
+	if (con->sock) {
+		sock_release(con->sock);
+		con->sock = NULL;
+	}
+	if (con->othercon && and_other) {
+		/* Will only re-enter once. */
+		close_connection(con->othercon, false);
+	}
+	if (con->rx_page) {
+		__free_page(con->rx_page);
+		con->rx_page = NULL;
+	}
+	con->retries = 0;
+	mutex_unlock(&con->sock_mutex);
+}
+
+/* We only send shutdown messages to nodes that are not part of the cluster */
+static void sctp_send_shutdown(sctp_assoc_t associd)
+{
+	static char outcmsg[CMSG_SPACE(sizeof(struct sctp_sndrcvinfo))];
+	struct msghdr outmessage;
+	struct cmsghdr *cmsg;
+	struct sctp_sndrcvinfo *sinfo;
+	int ret;
+	struct connection *con;
+
+	con = nodeid2con(0,0);
+	BUG_ON(con == NULL);
+
+	outmessage.msg_name = NULL;
+	outmessage.msg_namelen = 0;
+	outmessage.msg_control = outcmsg;
+	outmessage.msg_controllen = sizeof(outcmsg);
+	outmessage.msg_flags = MSG_EOR;
+
+	cmsg = CMSG_FIRSTHDR(&outmessage);
+	cmsg->cmsg_level = IPPROTO_SCTP;
+	cmsg->cmsg_type = SCTP_SNDRCV;
+	cmsg->cmsg_len = CMSG_LEN(sizeof(struct sctp_sndrcvinfo));
+	outmessage.msg_controllen = cmsg->cmsg_len;
+	sinfo = CMSG_DATA(cmsg);
+	memset(sinfo, 0x00, sizeof(struct sctp_sndrcvinfo));
+
+	sinfo->sinfo_flags |= MSG_EOF;
+	sinfo->sinfo_assoc_id = associd;
+
+	ret = kernel_sendmsg(con->sock, &outmessage, NULL, 0, 0);
+
+	if (ret != 0)
+		log_print("send EOF to node failed: %d", ret);
+}
+
+/* INIT failed but we don't know which node...
+   restart INIT on all pending nodes */
+static void sctp_init_failed(void)
+{
+	int i;
+	struct connection *con;
+
+	down(&connections_lock);
+	for (i=1; i<=max_nodeid; i++) {
+		con = __nodeid2con(i, 0);
+		if (!con)
+			continue;
+		con->sctp_assoc = 0;
+		if (test_and_clear_bit(CF_CONNECT_PENDING, &con->flags)) {
+			if (!test_and_set_bit(CF_WRITE_PENDING, &con->flags)) {
+				queue_work(send_workqueue, &con->swork);
+			}
+		}
+	}
+	up(&connections_lock);
+}
+
+/* Something happened to an association */
+static void process_sctp_notification(struct connection *con, struct msghdr *msg, char *buf)
+{
+	union sctp_notification *sn = (union sctp_notification *)buf;
+
+	if (sn->sn_header.sn_type == SCTP_ASSOC_CHANGE) {
+		switch (sn->sn_assoc_change.sac_state) {
+
+		case SCTP_COMM_UP:
+		case SCTP_RESTART:
+		{
+			/* Check that the new node is in the lockspace */
+			struct sctp_prim prim;
+			int nodeid;
+			int prim_len, ret;
+			int addr_len;
+			struct connection *new_con;
+			struct file *file;
+			sctp_peeloff_arg_t parg;
+			int parglen = sizeof(parg);
+
+			/*
+			 * We get this before any data for an association.
+			 * We verify that the node is in the cluster and
+			 * then peel off a socket for it.
+			 */
+			if ((int)sn->sn_assoc_change.sac_assoc_id <= 0) {
+				log_print("COMM_UP for invalid assoc ID %d",
+					  (int)sn->sn_assoc_change.sac_assoc_id);
+				sctp_init_failed();
+				return;
+			}
+			memset(&prim, 0, sizeof(struct sctp_prim));
+			prim_len = sizeof(struct sctp_prim);
+			prim.ssp_assoc_id = sn->sn_assoc_change.sac_assoc_id;
+
+			ret = kernel_getsockopt(con->sock,
+						IPPROTO_SCTP,
+						SCTP_PRIMARY_ADDR,
+						(char*)&prim,
+						&prim_len);
+			if (ret < 0) {
+				log_print("getsockopt/sctp_primary_addr on "
+					  "new assoc %d failed : %d",
+					  (int)sn->sn_assoc_change.sac_assoc_id,
+					  ret);
+
+				/* Retry INIT later */
+				new_con = assoc2con(sn->sn_assoc_change.sac_assoc_id);
+				if (new_con)
+					clear_bit(CF_CONNECT_PENDING, &con->flags);
+				return;
+			}
+			make_sockaddr(&prim.ssp_addr, 0, &addr_len);
+			if (dlm_addr_to_nodeid(&prim.ssp_addr, &nodeid)) {
+				int i;
+				unsigned char *b=(unsigned char *)&prim.ssp_addr;
+				log_print("reject connect from unknown addr");
+				for (i=0; i<sizeof(struct sockaddr_storage);i++)
+					printk("%02x ", b[i]);
+				printk("\n");
+				sctp_send_shutdown(prim.ssp_assoc_id);
+				return;
+			}
+
+			new_con = nodeid2con(nodeid, GFP_KERNEL);
+			if (!new_con)
+				return;
+
+			/* Peel off a new sock */
+			parg.associd = sn->sn_assoc_change.sac_assoc_id;
+			ret = kernel_getsockopt(con->sock, IPPROTO_SCTP, SCTP_SOCKOPT_PEELOFF,
+						(void *)&parg, &parglen);
+			if (ret < 0) {
+				log_print("Can't peel off a socket for connection %d to node %d: err=%d\n",
+					  parg.associd, nodeid, ret);
+				return;
+			}
+
+			file = fget(parg.sd);
+			new_con->sock = SOCKET_I(file->f_dentry->d_inode);
+			add_sock(new_con->sock, new_con);
+			fput(file);
+			put_unused_fd(parg.sd);
+
+			log_print("got new/restarted association %d nodeid %d",
+				  (int)sn->sn_assoc_change.sac_assoc_id, nodeid);
+
+			/* Send any pending writes */
+			clear_bit(CF_CONNECT_PENDING, &new_con->flags);
+			clear_bit(CF_INIT_PENDING, &con->flags);
+			if (!test_and_set_bit(CF_WRITE_PENDING, &new_con->flags)) {
+				queue_work(send_workqueue, &new_con->swork);
+			}
+			if (!test_and_set_bit(CF_READ_PENDING, &new_con->flags))
+				queue_work(recv_workqueue, &new_con->rwork);
+		}
+		break;
+
+		case SCTP_COMM_LOST:
+		case SCTP_SHUTDOWN_COMP:
+		{
+			con = assoc2con(sn->sn_assoc_change.sac_assoc_id);
+			if (con) {
+				con->sctp_assoc = 0;
+			}
+		}
+		break;
+
+		/* We don't know which INIT failed, so clear the PENDING flags
+		 * on them all.  if assoc_id is zero then it will then try
+		 * again */
+
+		case SCTP_CANT_STR_ASSOC:
+		{
+			log_print("Can't start SCTP association - retrying");
+			sctp_init_failed();
+		}
+		break;
+
+		default:
+			log_print("unexpected SCTP assoc change id=%d state=%d",
+				  (int)sn->sn_assoc_change.sac_assoc_id,
+				  sn->sn_assoc_change.sac_state);
+		}
+	}
+}
+
+/* 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;
+	char incmsg[CMSG_SPACE(sizeof(struct sctp_sndrcvinfo))];
+
+	mutex_lock(&con->sock_mutex);
+
+	if (con->sock == NULL) {
+		ret = -EAGAIN;
+		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_CACHE_SIZE);
+	}
+
+	/* Only SCTP needs these really */
+	memset(&incmsg, 0, sizeof(incmsg));
+	msg.msg_control = incmsg;
+	msg.msg_controllen = sizeof(incmsg);
+
+	/*
+	 * 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_CACHE_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;
+
+	r = ret = kernel_recvmsg(con->sock, &msg, iov, nvec, len,
+			       MSG_DONTWAIT | MSG_NOSIGNAL);
+	if (ret <= 0)
+		goto out_close;
+
+	/* Process SCTP notifications */
+	if (msg.msg_flags & MSG_NOTIFICATION) {
+		BUG_ON(con->nodeid != 0);
+		msg.msg_control = incmsg;
+		msg.msg_controllen = sizeof(incmsg);
+
+		process_sctp_notification(con, &msg,
+					  page_address(con->rx_page) + con->cb.base);
+		mutex_unlock(&con->sock_mutex);
+		return 0;
+	}
+	BUG_ON(con->nodeid == 0);
+
+	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_CACHE_SIZE);
+	if (ret == -EBADMSG) {
+		printk(KERN_INFO "dlm: lowcomms: addr=%p, base=%u, len=%u, "
+		       "iov_len=%u, iov_base[0]=%p, read=%d\n",
+		       page_address(con->rx_page), con->cb.base, con->cb.len,
+		       len, iov[0].iov_base, 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 && !test_bit(CF_IS_OTHERCON, &con->flags)) {
+		close_connection(con, 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 tcp_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;
+
+	memset(&peeraddr, 0, sizeof(peeraddr));
+	result = sock_create_kern(dlm_local_addr[0]->ss_family, SOCK_STREAM,
+				  IPPROTO_TCP, &newsock);
+	if (result < 0)
+		return -ENOMEM;
+
+	mutex_lock_nested(&con->sock_mutex, 0);
+
+	result = -ENOTCONN;
+	if (con->sock == NULL)
+		goto accept_err;
+
+	newsock->type = con->sock->type;
+	newsock->ops = con->sock->ops;
+
+	result = con->sock->ops->accept(con->sock, newsock, O_NONBLOCK);
+	if (result < 0)
+		goto accept_err;
+
+	/* Get the connected socket's peer */
+	memset(&peeraddr, 0, sizeof(peeraddr));
+	if (newsock->ops->getname(newsock, (struct sockaddr *)&peeraddr,
+				  &len, 2)) {
+		result = -ECONNABORTED;
+		goto accept_err;
+	}
+
+	/* Get the new node's NODEID */
+	make_sockaddr(&peeraddr, 0, &len);
+	if (dlm_addr_to_nodeid(&peeraddr, &nodeid)) {
+		printk("dlm: connect from non cluster node\n");
+		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_KERNEL);
+	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_KERNEL);
+			if (!othercon) {
+				printk("dlm: failed to allocate incoming socket\n");
+				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_WORK(&othercon->swork, process_send_sockets);
+			INIT_WORK(&othercon->rwork, process_recv_sockets);
+			set_bit(CF_IS_OTHERCON, &othercon->flags);
+			newcon->othercon = othercon;
+		}
+		othercon->sock = newsock;
+		newsock->sk->sk_user_data = othercon;
+		add_sock(newsock, othercon);
+		addcon = othercon;
+	}
+	else {
+		newsock->sk->sk_user_data = newcon;
+		newcon->rx_action = receive_from_sock;
+		add_sock(newsock, newcon);
+		addcon = newcon;
+	}
+
+	mutex_unlock(&newcon->sock_mutex);
+
+	/*
+	 * Add it to the active queue in case we got data
+	 * beween 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);
+	sock_release(newsock);
+
+	if (result != -EAGAIN)
+		printk("dlm: error accepting connection from node: %d\n", result);
+	return result;
+}
+
+static void free_entry(struct writequeue_entry *e)
+{
+	__free_page(e->page);
+	kfree(e);
+}
+
+/* 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_init_assoc(struct connection *con)
+{
+	struct sockaddr_storage rem_addr;
+	char outcmsg[CMSG_SPACE(sizeof(struct sctp_sndrcvinfo))];
+	struct msghdr outmessage;
+	struct cmsghdr *cmsg;
+	struct sctp_sndrcvinfo *sinfo;
+	struct connection *base_con;
+	struct writequeue_entry *e;
+	int len, offset;
+	int ret;
+	int addrlen;
+	struct kvec iov[1];
+
+	if (test_and_set_bit(CF_INIT_PENDING, &con->flags))
+		return;
+
+	if (con->retries++ > MAX_CONNECT_RETRIES)
+		return;
+
+	log_print("Initiating association with node %d", con->nodeid);
+
+	if (nodeid_to_addr(con->nodeid, (struct sockaddr *)&rem_addr)) {
+		log_print("no address for nodeid %d", con->nodeid);
+		return;
+	}
+	base_con = nodeid2con(0, 0);
+	BUG_ON(base_con == NULL);
+
+	make_sockaddr(&rem_addr, dlm_config.ci_tcp_port, &addrlen);
+
+	outmessage.msg_name = &rem_addr;
+	outmessage.msg_namelen = addrlen;
+	outmessage.msg_control = outcmsg;
+	outmessage.msg_controllen = sizeof(outcmsg);
+	outmessage.msg_flags = MSG_EOR;
+
+	spin_lock(&con->writequeue_lock);
+	e = list_entry(con->writequeue.next, struct writequeue_entry,
+		       list);
+
+	BUG_ON((struct list_head *) e == &con->writequeue);
+
+	len = e->len;
+	offset = e->offset;
+	spin_unlock(&con->writequeue_lock);
+	kmap(e->page);
+
+	/* Send the first block off the write queue */
+	iov[0].iov_base = page_address(e->page)+offset;
+	iov[0].iov_len = len;
+
+	cmsg = CMSG_FIRSTHDR(&outmessage);
+	cmsg->cmsg_level = IPPROTO_SCTP;
+	cmsg->cmsg_type = SCTP_SNDRCV;
+	cmsg->cmsg_len = CMSG_LEN(sizeof(struct sctp_sndrcvinfo));
+	sinfo = CMSG_DATA(cmsg);
+	memset(sinfo, 0x00, sizeof(struct sctp_sndrcvinfo));
+	sinfo->sinfo_ppid = cpu_to_le32(dlm_our_nodeid());
+	outmessage.msg_controllen = cmsg->cmsg_len;
+
+	ret = kernel_sendmsg(base_con->sock, &outmessage, iov, 1, len);
+	if (ret < 0) {
+		log_print("Send first packet to node %d failed: %d", con->nodeid, ret);
+
+		/* Try again later */
+		clear_bit(CF_CONNECT_PENDING, &con->flags);
+		clear_bit(CF_INIT_PENDING, &con->flags);
+	}
+	else {
+		spin_lock(&con->writequeue_lock);
+		e->offset += ret;
+		e->len -= ret;
+
+		if (e->len == 0 && e->users == 0) {
+			list_del(&e->list);
+			kunmap(e->page);
+			free_entry(e);
+		}
+		spin_unlock(&con->writequeue_lock);
+	}
+}
+
+/* Connect a new socket to its peer */
+static void tcp_connect_to_sock(struct connection *con)
+{
+	int result = -EHOSTUNREACH;
+	struct sockaddr_storage saddr;
+	int addr_len;
+	struct socket *sock;
+
+	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) {
+		result = 0;
+		goto out;
+	}
+
+	/* Create a socket to communicate with */
+	result = sock_create_kern(dlm_local_addr[0]->ss_family, SOCK_STREAM,
+				  IPPROTO_TCP, &sock);
+	if (result < 0)
+		goto out_err;
+
+	memset(&saddr, 0, sizeof(saddr));
+	if (dlm_nodeid_to_addr(con->nodeid, &saddr))
+		goto out_err;
+
+	sock->sk->sk_user_data = con;
+	con->rx_action = receive_from_sock;
+	con->connect_action = tcp_connect_to_sock;
+	add_sock(sock, con);
+
+	make_sockaddr(&saddr, dlm_config.ci_tcp_port, &addr_len);
+
+	log_print("connecting to %d", con->nodeid);
+	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;
+	}
+	/*
+	 * 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) {
+		lowcomms_connect_sock(con);
+		result = 0;
+	}
+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 one = 1;
+	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(dlm_local_addr[0]->ss_family, SOCK_STREAM, IPPROTO_TCP, &sock);
+	if (result < 0) {
+		printk("dlm: Can't create listening comms socket\n");
+		goto create_out;
+	}
+
+	result = kernel_setsockopt(sock, SOL_SOCKET, SO_REUSEADDR,
+				   (char *)&one, sizeof(one));
+
+	if (result < 0) {
+		printk("dlm: Failed to set SO_REUSEADDR on socket: result=%d\n",
+		       result);
+	}
+	sock->sk->sk_user_data = con;
+	con->rx_action = tcp_accept_from_sock;
+	con->connect_action = tcp_connect_to_sock;
+	con->sock = sock;
+
+	/* 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) {
+		printk("dlm: Can't bind to port %d\n", dlm_config.ci_tcp_port);
+		sock_release(sock);
+		sock = NULL;
+		con->sock = NULL;
+		goto create_out;
+	}
+	result = kernel_setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE,
+				 (char *)&one, sizeof(one));
+	if (result < 0) {
+		printk("dlm: Set keepalive failed: %d\n", result);
+	}
+
+	result = sock->ops->listen(sock, 5);
+	if (result < 0) {
+		printk("dlm: Can't listen on port %d\n", 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;
+
+	for (i = 0; i < DLM_MAX_ADDR_COUNT - 1; i++) {
+		if (dlm_our_addr(&sas, i))
+			break;
+
+		addr = kmalloc(sizeof(*addr), GFP_KERNEL);
+		if (!addr)
+			break;
+		memcpy(addr, &sas, sizeof(*addr));
+		dlm_local_addr[dlm_local_count++] = addr;
+	}
+}
+
+/* Bind to an IP address. SCTP allows multiple address so it can do multi-homing */
+static int add_sctp_bind_addr(struct connection *sctp_con, struct sockaddr_storage *addr, int addr_len, int num)
+{
+	int result = 0;
+
+	if (num == 1)
+		result = kernel_bind(sctp_con->sock,
+				     (struct sockaddr *) addr,
+				     addr_len);
+	else
+		result = kernel_setsockopt(sctp_con->sock, SOL_SCTP,
+					   SCTP_SOCKOPT_BINDX_ADD,
+					   (char *)addr, addr_len);
+
+	if (result < 0)
+		log_print("Can't bind to port %d addr number %d",
+			  dlm_config.ci_tcp_port, num);
+
+	return result;
+}
+
+/* Initialise SCTP socket and bind to all interfaces */
+static int sctp_listen_for_all(void)
+{
+	struct socket *sock = NULL;
+	struct sockaddr_storage localaddr;
+	struct sctp_event_subscribe subscribe;
+	int result = -EINVAL, num = 1, i, addr_len;
+	struct connection *con = nodeid2con(0, GFP_KERNEL);
+	int bufsize = NEEDED_RMEM;
+
+	if (!con)
+		return -ENOMEM;
+
+	log_print("Using SCTP for communications");
+
+	result = sock_create_kern(dlm_local_addr[0]->ss_family, SOCK_SEQPACKET,
+				  IPPROTO_SCTP, &sock);
+	if (result < 0) {
+		log_print("Can't create comms socket, check SCTP is loaded");
+		goto out;
+	}
+
+	/* Listen for events */
+	memset(&subscribe, 0, sizeof(subscribe));
+	subscribe.sctp_data_io_event = 1;
+	subscribe.sctp_association_event = 1;
+	subscribe.sctp_send_failure_event = 1;
+	subscribe.sctp_shutdown_event = 1;
+	subscribe.sctp_partial_delivery_event = 1;
+
+	result = kernel_setsockopt(sock, SOL_SOCKET, SO_RCVBUF,
+				 (char *)&bufsize, sizeof(bufsize));
+	if (result)
+		log_print("Error increasing buffer space on socket: %d", result);
+
+	result = kernel_setsockopt(sock, SOL_SCTP, SCTP_EVENTS,
+				       (char *)&subscribe, sizeof(subscribe));
+	if (result < 0) {
+		log_print("Failed to set SCTP_EVENTS on socket: result=%d",
+			  result);
+		goto create_delsock;
+	}
+
+	/* Init con struct */
+	sock->sk->sk_user_data = con;
+	con->sock = sock;
+	con->sock->sk->sk_data_ready = lowcomms_data_ready;
+	con->rx_action = receive_from_sock;
+	con->connect_action = sctp_init_assoc;
+
+	/* Bind to all interfaces. */
+	for (i = 0; i < dlm_local_count; i++) {
+		memcpy(&localaddr, dlm_local_addr[i], sizeof(localaddr));
+		make_sockaddr(&localaddr, dlm_config.ci_tcp_port, &addr_len);
+
+		result = add_sctp_bind_addr(con, &localaddr, addr_len, num);
+		if (result)
+			goto create_delsock;
+		++num;
+	}
+
+	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_KERNEL);
+	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");
+
+	set_bit(CF_IS_OTHERCON, &con->flags);
+
+	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;
+	int users = 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_CACHE_SIZE - e->end < len)) {
+		e = NULL;
+	} else {
+		offset = e->end;
+		e->end += len;
+		users = e->users++;
+	}
+	spin_unlock(&con->writequeue_lock);
+
+	if (e) {
+	got_one:
+		if (users == 0)
+			kmap(e->page);
+		*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;
+		users = 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;
+	kunmap(e->page);
+	spin_unlock(&con->writequeue_lock);
+
+	if (!test_and_set_bit(CF_WRITE_PENDING, &con->flags)) {
+		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;
+	ssize_t(*sendpage) (struct socket *, struct page *, int, size_t, int);
+	const int msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL;
+	struct writequeue_entry *e;
+	int len, offset;
+
+	mutex_lock(&con->sock_mutex);
+	if (con->sock == NULL)
+		goto out_connect;
+
+	sendpage = con->sock->ops->sendpage;
+
+	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);
+		kmap(e->page);
+
+		ret = 0;
+		if (len) {
+			ret = sendpage(con->sock, e->page, offset, len,
+				       msg_flags);
+			if (ret == -EAGAIN || ret == 0)
+				goto out;
+			if (ret <= 0)
+				goto send_error;
+		}
+		else {
+			/* Don't starve people filling buffers */
+			cond_resched();
+		}
+
+		spin_lock(&con->writequeue_lock);
+		e->offset += ret;
+		e->len -= ret;
+
+		if (e->len == 0 && e->users == 0) {
+			list_del(&e->list);
+			kunmap(e->page);
+			free_entry(e);
+			continue;
+		}
+	}
+	spin_unlock(&con->writequeue_lock);
+out:
+	mutex_unlock(&con->sock_mutex);
+	return;
+
+send_error:
+	mutex_unlock(&con->sock_mutex);
+	close_connection(con, false);
+	lowcomms_connect_sock(con);
+	return;
+
+out_connect:
+	mutex_unlock(&con->sock_mutex);
+	if (!test_bit(CF_INIT_PENDING, &con->flags))
+		lowcomms_connect_sock(con);
+	return;
+}
+
+static void clean_one_writequeue(struct connection *con)
+{
+	struct list_head *list;
+	struct list_head *temp;
+
+	spin_lock(&con->writequeue_lock);
+	list_for_each_safe(list, temp, &con->writequeue) {
+		struct writequeue_entry *e =
+			list_entry(list, struct writequeue_entry, 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;
+
+	log_print("closing connection to node %d", nodeid);
+	con = nodeid2con(nodeid, 0);
+	if (con) {
+		clean_one_writequeue(con);
+		close_connection(con, true);
+	}
+	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);
+
+	if (test_and_clear_bit(CF_CONNECT_PENDING, &con->flags)) {
+		con->connect_action(con);
+	}
+	clear_bit(CF_WRITE_PENDING, &con->flags);
+	send_to_sock(con);
+}
+
+
+/* Discard all entries on the write queues */
+static void clean_writequeues(void)
+{
+	int nodeid;
+
+	for (nodeid = 1; nodeid < max_nodeid; nodeid++) {
+		struct connection *con = nodeid2con(nodeid, 0);
+
+		if (con)
+			clean_one_writequeue(con);
+	}
+}
+
+static void work_stop(void)
+{
+	destroy_workqueue(recv_workqueue);
+	destroy_workqueue(send_workqueue);
+}
+
+static int work_start(void)
+{
+	int error;
+	recv_workqueue = create_workqueue("dlm_recv");
+	error = IS_ERR(recv_workqueue);
+	if (error) {
+		log_print("can't start dlm_recv %d", error);
+		return error;
+	}
+
+	send_workqueue = create_singlethread_workqueue("dlm_send");
+	error = IS_ERR(send_workqueue);
+	if (error) {
+		log_print("can't start dlm_send %d", error);
+		destroy_workqueue(recv_workqueue);
+		return error;
+	}
+
+	return 0;
+}
+
+void dlm_lowcomms_stop(void)
+{
+	int i;
+	struct connection *con;
+
+	/* Set all the flags to prevent any
+	   socket activity.
+	*/
+	down(&connections_lock);
+	for (i = 0; i < max_nodeid; i++) {
+		con = __nodeid2con(i, 0);
+		if (con)
+			con->flags |= 0xFF;
+	}
+	up(&connections_lock);
+
+	work_stop();
+
+	down(&connections_lock);
+	clean_writequeues();
+
+	for (i = 0; i < max_nodeid; i++) {
+		con = nodeid2con(i, 0);
+		if (con) {
+			close_connection(con, true);
+			if (con->othercon)
+				kmem_cache_free(con_cache, con->othercon);
+			kmem_cache_free(con_cache, con);
+		}
+	}
+	up(&connections_lock);
+	kmem_cache_destroy(con_cache);
+}
+
+int dlm_lowcomms_start(void)
+{
+	int error = -EINVAL;
+	struct connection *con;
+
+	init_local();
+	if (!dlm_local_count) {
+		log_print("no local IP address has been set");
+		goto out;
+	}
+
+	error = -ENOMEM;
+	con_cache = kmem_cache_create("dlm_conn", sizeof(struct connection),
+				      __alignof__(struct connection), 0,
+				      NULL, NULL);
+	if (!con_cache)
+		goto out;
+
+	/* Set some sysctl minima */
+	if (sysctl_rmem_max < NEEDED_RMEM)
+		sysctl_rmem_max = NEEDED_RMEM;
+
+	/* Start listening */
+	if (dlm_config.ci_protocol == 0)
+		error = tcp_listen_for_all();
+	else
+		error = sctp_listen_for_all();
+	if (error)
+		goto fail_unlisten;
+
+	error = work_start();
+	if (error)
+		goto fail_unlisten;
+
+	return 0;
+
+fail_unlisten:
+	con = nodeid2con(0,0);
+	if (con) {
+		close_connection(con, false);
+		kmem_cache_free(con_cache, con);
+	}
+	kmem_cache_destroy(con_cache);
+
+out:
+	return error;
+}