[DLM] Add support for tcp communications

The following patch adds a TCP based communications layer
to the DLM which is compile time selectable. The existing SCTP
layer gives the advantage of allowing multihoming, whereas
the TCP layer has been heavily tested in previous versions of
the DLM and is known to be robust and therefore can be used as
a baseline for performance testing.

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

1 files changed, 1263 insertions, 0 deletions

diff --git a/fs/dlm/lowcomms-tcp.c b/fs/dlm/lowcomms-tcp.c
new file mode 100644
index 000000000000..7289e59b4bd3
--- /dev/null
+++ b/fs/dlm/lowcomms-tcp.c
@@ -0,0 +1,1263 @@
+/******************************************************************************
+*******************************************************************************
+**
+**  Copyright (C) Sistina Software, Inc.  1997-2003  All rights reserved.
+**  Copyright (C) 2004-2006 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.
+ *
+ * I don't see any problem with the recv thread executing the locking
+ * code on behalf of remote processes as the locking code is
+ * short, efficient and never waits.
+ *
+ */
+
+
+#include <asm/ioctls.h>
+#include <net/sock.h>
+#include <net/tcp.h>
+#include <linux/pagemap.h>
+
+#include "dlm_internal.h"
+#include "lowcomms.h"
+#include "midcomms.h"
+#include "config.h"
+
+struct cbuf {
+	unsigned base;
+	unsigned len;
+	unsigned mask;
+};
+
+#ifndef FALSE
+#define FALSE 0
+#define TRUE 1
+#endif
+#define NODE_INCREMENT 32
+
+#define CBUF_INIT(cb, size) do { (cb)->base = (cb)->len = 0; (cb)->mask = ((size)-1); } while(0)
+#define CBUF_ADD(cb, n) do { (cb)->len += n; } while(0)
+#define CBUF_EMPTY(cb) ((cb)->len == 0)
+#define CBUF_MAY_ADD(cb, n) (((cb)->len + (n)) < ((cb)->mask + 1))
+#define CBUF_EAT(cb, n) do { (cb)->len  -= (n); \
+                             (cb)->base += (n); (cb)->base &= (cb)->mask; } while(0)
+#define CBUF_DATA(cb) (((cb)->base + (cb)->len) & (cb)->mask)
+
+/* Maximum number of incoming messages to process before
+   doing a schedule()
+*/
+#define MAX_RX_MSG_COUNT 25
+
+struct connection {
+	struct socket *sock;	/* NULL if not connected */
+	uint32_t nodeid;	/* So we know who we are in the list */
+	struct rw_semaphore sock_sem;	/* Stop connect races */
+	struct list_head read_list;	/* On this list when ready for reading */
+	struct list_head write_list;	/* On this list when ready for writing */
+	struct list_head state_list;	/* On this list when ready to connect */
+	unsigned long flags;	/* bit 1,2 = We are on the read/write lists */
+#define CF_READ_PENDING 1
+#define CF_WRITE_PENDING 2
+#define CF_CONNECT_PENDING 3
+#define CF_IS_OTHERCON 4
+	struct list_head writequeue;	/* List of outgoing writequeue_entries */
+	struct list_head listenlist;    /* List of allocated listening sockets */
+	spinlock_t writequeue_lock;
+	int (*rx_action) (struct connection *);	/* What to do when active */
+	struct page *rx_page;
+	struct cbuf cb;
+	int retries;
+	atomic_t waiting_requests;
+#define MAX_CONNECT_RETRIES 3
+	struct connection *othercon;
+};
+#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;
+
+/* Manage daemons */
+static struct task_struct *recv_task;
+static struct task_struct *send_task;
+
+static wait_queue_t lowcomms_send_waitq_head;
+static wait_queue_head_t lowcomms_send_waitq;
+static wait_queue_t lowcomms_recv_waitq_head;
+static wait_queue_head_t lowcomms_recv_waitq;
+
+/* An array of pointers to connections, indexed by NODEID */
+static struct connection **connections;
+static struct semaphore connections_lock;
+static kmem_cache_t *con_cache;
+static int conn_array_size;
+static atomic_t accepting;
+
+/* List of sockets that have reads pending */
+static struct list_head read_sockets;
+static spinlock_t read_sockets_lock;
+
+/* List of sockets which have writes pending */
+static struct list_head write_sockets;
+static spinlock_t write_sockets_lock;
+
+/* List of sockets which have connects pending */
+static struct list_head state_sockets;
+static spinlock_t state_sockets_lock;
+
+static struct connection *nodeid2con(int nodeid, gfp_t allocation)
+{
+	struct connection *con = NULL;
+
+	down(&connections_lock);
+	if (nodeid >= conn_array_size) {
+		int new_size = nodeid + NODE_INCREMENT;
+		struct connection **new_conns;
+
+		new_conns = kmalloc(sizeof(struct connection *) *
+				    new_size, allocation);
+		if (!new_conns)
+			goto finish;
+
+		memset(new_conns, 0, sizeof(struct connection *) * new_size);
+		memcpy(new_conns, connections,  sizeof(struct connection *) * conn_array_size);
+		conn_array_size = new_size;
+		kfree(connections);
+		connections = new_conns;
+
+	}
+
+	con = connections[nodeid];
+	if (con == NULL && allocation) {
+		con = kmem_cache_alloc(con_cache, allocation);
+		if (!con)
+			goto finish;
+
+		memset(con, 0, sizeof(*con));
+		con->nodeid = nodeid;
+		init_rwsem(&con->sock_sem);
+		INIT_LIST_HEAD(&con->writequeue);
+		spin_lock_init(&con->writequeue_lock);
+
+		connections[nodeid] = con;
+	}
+
+ finish:
+	up(&connections_lock);
+	return con;
+}
+
+/* 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);
+
+	atomic_inc(&con->waiting_requests);
+	if (test_and_set_bit(CF_READ_PENDING, &con->flags))
+		return;
+
+	spin_lock_bh(&read_sockets_lock);
+	list_add_tail(&con->read_list, &read_sockets);
+	spin_unlock_bh(&read_sockets_lock);
+
+	wake_up_interruptible(&lowcomms_recv_waitq);
+}
+
+static void lowcomms_write_space(struct sock *sk)
+{
+	struct connection *con = sock2con(sk);
+
+	if (test_and_set_bit(CF_WRITE_PENDING, &con->flags))
+		return;
+
+	spin_lock_bh(&write_sockets_lock);
+	list_add_tail(&con->write_list, &write_sockets);
+	spin_unlock_bh(&write_sockets_lock);
+
+	wake_up_interruptible(&lowcomms_send_waitq);
+}
+
+static inline void lowcomms_connect_sock(struct connection *con)
+{
+	if (test_and_set_bit(CF_CONNECT_PENDING, &con->flags))
+		return;
+	if (!atomic_read(&accepting))
+		return;
+
+	spin_lock_bh(&state_sockets_lock);
+	list_add_tail(&con->state_list, &state_sockets);
+	spin_unlock_bh(&state_sockets_lock);
+
+	wake_up_interruptible(&lowcomms_send_waitq);
+}
+
+static void lowcomms_state_change(struct sock *sk)
+{
+/*	struct connection *con = sock2con(sk); */
+
+	switch (sk->sk_state) {
+	case TCP_ESTABLISHED:
+		lowcomms_write_space(sk);
+		break;
+
+	case TCP_FIN_WAIT1:
+	case TCP_FIN_WAIT2:
+	case TCP_TIME_WAIT:
+	case TCP_CLOSE:
+	case TCP_CLOSE_WAIT:
+	case TCP_LAST_ACK:
+	case TCP_CLOSING:
+		/* FIXME: I think this causes more trouble than it solves.
+		   lowcomms wil reconnect anyway when there is something to
+		   send. This just attempts reconnection if a node goes down!
+		*/
+		/* lowcomms_connect_sock(con); */
+		break;
+
+	default:
+		printk("dlm: lowcomms_state_change: state=%d\n", sk->sk_state);
+		break;
+	}
+}
+
+/* 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;
+
+	return 0;
+}
+
+/* Add the port number to an IP6 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.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);
+	}
+	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, int and_other)
+{
+	down_write(&con->sock_sem);
+
+	if (con->sock) {
+		sock_release(con->sock);
+		con->sock = NULL;
+	}
+	if (con->othercon && and_other) {
+		/* Argh! recursion in kernel code!
+		   Actually, this isn't a list so it
+		   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;
+	up_write(&con->sock_sem);
+}
+
+/* Data received from remote end */
+static int receive_from_sock(struct connection *con)
+{
+	int ret = 0;
+	struct msghdr msg;
+	struct iovec iov[2];
+	mm_segment_t fs;
+	unsigned len;
+	int r;
+	int call_again_soon = 0;
+
+	down_read(&con->sock_sem);
+
+	if (con->sock == NULL)
+		goto out;
+	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);
+	}
+
+	msg.msg_control = NULL;
+	msg.msg_controllen = 0;
+	msg.msg_iovlen = 1;
+	msg.msg_iov = iov;
+	msg.msg_name = NULL;
+	msg.msg_namelen = 0;
+	msg.msg_flags = 0;
+
+	/*
+	 * 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;
+
+	/*
+	 * 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);
+		msg.msg_iovlen = 2;
+	}
+	len = iov[0].iov_len + iov[1].iov_len;
+
+	fs = get_fs();
+	set_fs(get_ds());
+	r = ret = sock_recvmsg(con->sock, &msg, len,
+			       MSG_DONTWAIT | MSG_NOSIGNAL);
+	set_fs(fs);
+
+	if (ret <= 0)
+		goto out_close;
+	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;
+	}
+
+      out:
+	if (call_again_soon)
+		goto out_resched;
+	up_read(&con->sock_sem);
+	ret = 0;
+	goto out_ret;
+
+      out_resched:
+	lowcomms_data_ready(con->sock->sk, 0);
+	up_read(&con->sock_sem);
+	ret = 0;
+	schedule();
+	goto out_ret;
+
+      out_close:
+	up_read(&con->sock_sem);
+	if (ret != -EAGAIN && !test_bit(CF_IS_OTHERCON, &con->flags)) {
+		close_connection(con, FALSE);
+		/* Reconnect when there is something to send */
+	}
+
+      out_ret:
+	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;
+
+	memset(&peeraddr, 0, sizeof(peeraddr));
+	result = sock_create_kern(dlm_local_addr.ss_family, SOCK_STREAM, IPPROTO_TCP, &newsock);
+	if (result < 0)
+		return -ENOMEM;
+
+	down_read(&con->sock_sem);
+
+	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);
+		up_read(&con->sock_sem);
+		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.
+	 * TEMPORARY FIX:
+	 *  In this case we store the incoming one in "othercon"
+	 */
+	newcon = nodeid2con(nodeid, GFP_KERNEL);
+	if (!newcon) {
+		result = -ENOMEM;
+		goto accept_err;
+	}
+	down_write(&newcon->sock_sem);
+	if (newcon->sock) {
+	        struct connection *othercon = newcon->othercon;
+
+		if (!othercon) {
+			othercon = kmem_cache_alloc(con_cache, GFP_KERNEL);
+			if (!othercon) {
+				printk("dlm: failed to allocate incoming socket\n");
+				up_write(&newcon->sock_sem);
+				result = -ENOMEM;
+				goto accept_err;
+			}
+			memset(othercon, 0, sizeof(*othercon));
+			othercon->nodeid = nodeid;
+			othercon->rx_action = receive_from_sock;
+			init_rwsem(&othercon->sock_sem);
+			set_bit(CF_IS_OTHERCON, &othercon->flags);
+			newcon->othercon = othercon;
+		}
+		othercon->sock = newsock;
+		newsock->sk->sk_user_data = othercon;
+		add_sock(newsock, othercon);
+	}
+	else {
+		newsock->sk->sk_user_data = newcon;
+		newcon->rx_action = receive_from_sock;
+		add_sock(newsock, newcon);
+
+	}
+
+	up_write(&newcon->sock_sem);
+
+	/*
+	 * Add it to the active queue in case we got data
+	 * beween processing the accept adding the socket
+	 * to the read_sockets list
+	 */
+	lowcomms_data_ready(newsock->sk, 0);
+	up_read(&con->sock_sem);
+
+	return 0;
+
+      accept_err:
+	up_read(&con->sock_sem);
+	sock_release(newsock);
+
+	if (result != -EAGAIN)
+		printk("dlm: error accepting connection from node: %d\n", result);
+	return result;
+}
+
+/* Connect a new socket to its peer */
+static int 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 0;
+	}
+
+	down_write(&con->sock_sem);
+	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.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;
+
+	make_sockaddr(&saddr, dlm_config.tcp_port, &addr_len);
+
+	add_sock(sock, con);
+
+	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_err;
+
+      out:
+	up_write(&con->sock_sem);
+	/*
+	 * Returning an error here means we've given up trying to connect to
+	 * a remote node, otherwise we return 0 and reschedule the connetion
+	 * attempt
+	 */
+	return result;
+
+      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;
+	}
+	goto out;
+}
+
+static struct socket *create_listen_sock(struct connection *con, struct sockaddr_storage *saddr)
+{
+        struct socket *sock = NULL;
+	mm_segment_t fs;
+	int result = 0;
+	int one = 1;
+	int addr_len;
+
+	if (dlm_local_addr.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.ss_family, SOCK_STREAM, IPPROTO_TCP, &sock);
+	if (result < 0) {
+		printk("dlm: Can't create listening comms socket\n");
+		goto create_out;
+	}
+
+	fs = get_fs();
+	set_fs(get_ds());
+	result = sock_setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (char *)&one, sizeof(one));
+	set_fs(fs);
+	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 = accept_from_sock;
+	con->sock = sock;
+
+	/* Bind to our port */
+	make_sockaddr(saddr, dlm_config.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.tcp_port);
+		sock_release(sock);
+		sock = NULL;
+		con->sock = NULL;
+		goto create_out;
+	}
+
+	fs = get_fs();
+	set_fs(get_ds());
+
+	result = sock_setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (char *)&one, sizeof(one));
+	set_fs(fs);
+	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.tcp_port);
+		sock_release(sock);
+		sock = NULL;
+		goto create_out;
+	}
+
+      create_out:
+	return sock;
+}
+
+
+/* Listen on all interfaces */
+static int listen_for_all(void)
+{
+	struct socket *sock = NULL;
+	struct connection *con = nodeid2con(0, GFP_KERNEL);
+	int result = -EINVAL;
+
+	/* We don't support multi-homed hosts */
+	memset(con, 0, sizeof(*con));
+	init_rwsem(&con->sock_sem);
+	spin_lock_init(&con->writequeue_lock);
+	INIT_LIST_HEAD(&con->writequeue);
+	set_bit(CF_IS_OTHERCON, &con->flags);
+
+	sock = create_listen_sock(con, &dlm_local_addr);
+	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;
+
+	if (!atomic_read(&accepting))
+		return NULL;
+
+	con = nodeid2con(nodeid, allocation);
+	if (!con)
+		return NULL;
+
+	spin_lock(&con->writequeue_lock);
+	e = list_entry(con->writequeue.prev, struct writequeue_entry, list);
+	if (((struct list_head *) e == &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;
+
+	if (!atomic_read(&accepting))
+		return;
+
+	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) == 0) {
+		spin_lock_bh(&write_sockets_lock);
+		list_add_tail(&con->write_list, &write_sockets);
+		spin_unlock_bh(&write_sockets_lock);
+
+		wake_up_interruptible(&lowcomms_send_waitq);
+	}
+	return;
+
+      out:
+	spin_unlock(&con->writequeue_lock);
+	return;
+}
+
+static void free_entry(struct writequeue_entry *e)
+{
+	__free_page(e->page);
+	kfree(e);
+}
+
+/* Send a message */
+static int 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;
+
+	down_read(&con->sock_sem);
+	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);
+
+		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 */
+			schedule();
+		}
+
+		spin_lock(&con->writequeue_lock);
+		e->offset += ret;
+		e->len -= ret;
+
+		if (e->len == 0 && e->users == 0) {
+			list_del(&e->list);
+			free_entry(e);
+			continue;
+		}
+	}
+	spin_unlock(&con->writequeue_lock);
+      out:
+	up_read(&con->sock_sem);
+	return ret;
+
+      send_error:
+	up_read(&con->sock_sem);
+	close_connection(con, FALSE);
+	lowcomms_connect_sock(con);
+	return ret;
+
+      out_connect:
+	up_read(&con->sock_sem);
+	lowcomms_connect_sock(con);
+	return 0;
+}
+
+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;
+
+	if (!connections)
+		goto out;
+
+	log_print("closing connection to node %d", nodeid);
+	con = nodeid2con(nodeid, 0);
+	if (con) {
+		clean_one_writequeue(con);
+		close_connection(con, TRUE);
+		atomic_set(&con->waiting_requests, 0);
+	}
+	return 0;
+
+      out:
+	return -1;
+}
+
+/* API send message call, may queue the request */
+/* N.B. This is the old interface - use the new one for new calls */
+int lowcomms_send_message(int nodeid, char *buf, int len, gfp_t allocation)
+{
+	struct writequeue_entry *e;
+	char *b;
+
+	e = dlm_lowcomms_get_buffer(nodeid, len, allocation, &b);
+	if (e) {
+		memcpy(b, buf, len);
+		dlm_lowcomms_commit_buffer(e);
+		return 0;
+	}
+	return -ENOBUFS;
+}
+
+/* Look for activity on active sockets */
+static void process_sockets(void)
+{
+	struct list_head *list;
+	struct list_head *temp;
+	int count = 0;
+
+	spin_lock_bh(&read_sockets_lock);
+	list_for_each_safe(list, temp, &read_sockets) {
+
+		struct connection *con =
+		    list_entry(list, struct connection, read_list);
+		list_del(&con->read_list);
+		clear_bit(CF_READ_PENDING, &con->flags);
+
+		spin_unlock_bh(&read_sockets_lock);
+
+		/* This can reach zero if we are processing requests
+		 * as they come in.
+		 */
+		if (atomic_read(&con->waiting_requests) == 0) {
+			spin_lock_bh(&read_sockets_lock);
+			continue;
+		}
+
+		do {
+			con->rx_action(con);
+
+			/* Don't starve out everyone else */
+			if (++count >= MAX_RX_MSG_COUNT) {
+				schedule();
+				count = 0;
+			}
+
+		} while (!atomic_dec_and_test(&con->waiting_requests) &&
+			 !kthread_should_stop());
+
+		spin_lock_bh(&read_sockets_lock);
+	}
+	spin_unlock_bh(&read_sockets_lock);
+}
+
+/* Try to send any messages that are pending
+ */
+static void process_output_queue(void)
+{
+	struct list_head *list;
+	struct list_head *temp;
+	int ret;
+
+	spin_lock_bh(&write_sockets_lock);
+	list_for_each_safe(list, temp, &write_sockets) {
+		struct connection *con =
+		    list_entry(list, struct connection, write_list);
+		clear_bit(CF_WRITE_PENDING, &con->flags);
+		list_del(&con->write_list);
+
+		spin_unlock_bh(&write_sockets_lock);
+
+		ret = send_to_sock(con);
+		if (ret < 0) {
+		}
+		spin_lock_bh(&write_sockets_lock);
+	}
+	spin_unlock_bh(&write_sockets_lock);
+}
+
+static void process_state_queue(void)
+{
+	struct list_head *list;
+	struct list_head *temp;
+	int ret;
+
+	spin_lock_bh(&state_sockets_lock);
+	list_for_each_safe(list, temp, &state_sockets) {
+		struct connection *con =
+		    list_entry(list, struct connection, state_list);
+		list_del(&con->state_list);
+		clear_bit(CF_CONNECT_PENDING, &con->flags);
+		spin_unlock_bh(&state_sockets_lock);
+
+		ret = connect_to_sock(con);
+		if (ret < 0) {
+		}
+		spin_lock_bh(&state_sockets_lock);
+	}
+	spin_unlock_bh(&state_sockets_lock);
+}
+
+
+/* Discard all entries on the write queues */
+static void clean_writequeues(void)
+{
+	int nodeid;
+
+	for (nodeid = 1; nodeid < conn_array_size; nodeid++) {
+		struct connection *con = nodeid2con(nodeid, 0);
+
+		if (con)
+			clean_one_writequeue(con);
+	}
+}
+
+static int read_list_empty(void)
+{
+	int status;
+
+	spin_lock_bh(&read_sockets_lock);
+	status = list_empty(&read_sockets);
+	spin_unlock_bh(&read_sockets_lock);
+
+	return status;
+}
+
+/* DLM Transport comms receive daemon */
+static int dlm_recvd(void *data)
+{
+	init_waitqueue_head(&lowcomms_recv_waitq);
+	init_waitqueue_entry(&lowcomms_recv_waitq_head, current);
+	add_wait_queue(&lowcomms_recv_waitq, &lowcomms_recv_waitq_head);
+
+	while (!kthread_should_stop()) {
+		set_current_state(TASK_INTERRUPTIBLE);
+		if (read_list_empty())
+			schedule();
+		set_current_state(TASK_RUNNING);
+
+		process_sockets();
+	}
+
+	return 0;
+}
+
+static int write_and_state_lists_empty(void)
+{
+	int status;
+
+	spin_lock_bh(&write_sockets_lock);
+	status = list_empty(&write_sockets);
+	spin_unlock_bh(&write_sockets_lock);
+
+	spin_lock_bh(&state_sockets_lock);
+	if (list_empty(&state_sockets) == 0)
+		status = 0;
+	spin_unlock_bh(&state_sockets_lock);
+
+	return status;
+}
+
+/* DLM Transport send daemon */
+static int dlm_sendd(void *data)
+{
+	init_waitqueue_head(&lowcomms_send_waitq);
+	init_waitqueue_entry(&lowcomms_send_waitq_head, current);
+	add_wait_queue(&lowcomms_send_waitq, &lowcomms_send_waitq_head);
+
+	while (!kthread_should_stop()) {
+		set_current_state(TASK_INTERRUPTIBLE);
+		if (write_and_state_lists_empty())
+			schedule();
+		set_current_state(TASK_RUNNING);
+
+		process_state_queue();
+		process_output_queue();
+	}
+
+	return 0;
+}
+
+static void daemons_stop(void)
+{
+	kthread_stop(recv_task);
+	kthread_stop(send_task);
+}
+
+static int daemons_start(void)
+{
+	struct task_struct *p;
+	int error;
+
+	p = kthread_run(dlm_recvd, NULL, "dlm_recvd");
+	error = IS_ERR(p);
+       	if (error) {
+		log_print("can't start dlm_recvd %d", error);
+		return error;
+	}
+	recv_task = p;
+
+	p = kthread_run(dlm_sendd, NULL, "dlm_sendd");
+	error = IS_ERR(p);
+       	if (error) {
+		log_print("can't start dlm_sendd %d", error);
+		kthread_stop(recv_task);
+		return error;
+	}
+	send_task = p;
+
+	return 0;
+}
+
+/*
+ * Return the largest buffer size we can cope with.
+ */
+int lowcomms_max_buffer_size(void)
+{
+	return PAGE_CACHE_SIZE;
+}
+
+void dlm_lowcomms_stop(void)
+{
+	int i;
+
+	atomic_set(&accepting, 0);
+
+	/* Set all the activity flags to prevent any
+	   socket activity.
+	*/
+	for (i = 0; i < conn_array_size; i++) {
+		if (connections[i])
+			connections[i]->flags |= 0x7;
+	}
+	daemons_stop();
+	clean_writequeues();
+
+	for (i = 0; i < conn_array_size; i++) {
+		if (connections[i]) {
+			close_connection(connections[i], TRUE);
+			if (connections[i]->othercon)
+				kmem_cache_free(con_cache, connections[i]->othercon);
+			kmem_cache_free(con_cache, connections[i]);
+		}
+	}
+
+	kfree(connections);
+	connections = NULL;
+
+	kmem_cache_destroy(con_cache);
+}
+
+/* This is quite likely to sleep... */
+int dlm_lowcomms_start(void)
+{
+	int error = 0;
+
+	error = -ENOTCONN;
+
+	/*
+	 * Temporarily initialise the waitq head so that lowcomms_send_message
+	 * doesn't crash if it gets called before the thread is fully
+	 * initialised
+	 */
+	init_waitqueue_head(&lowcomms_send_waitq);
+
+	error = -ENOMEM;
+	connections = kmalloc(sizeof(struct connection *) *
+			      NODE_INCREMENT, GFP_KERNEL);
+	if (!connections)
+		goto out;
+
+	memset(connections, 0,
+	       sizeof(struct connection *) * NODE_INCREMENT);
+
+	conn_array_size = NODE_INCREMENT;
+
+	if (dlm_our_addr(&dlm_local_addr, 0)) {
+		log_print("no local IP address has been set");
+		goto fail_free_conn;
+	}
+	if (!dlm_our_addr(&dlm_local_addr, 1)) {
+		log_print("This dlm comms module does not support multi-homed clustering");
+		goto fail_free_conn;
+	}
+
+	con_cache = kmem_cache_create("dlm_conn", sizeof(struct connection),
+				      __alignof__(struct connection), 0, NULL, NULL);
+	if (!con_cache)
+		goto fail_free_conn;
+
+
+	/* Start listening */
+	error = listen_for_all();
+	if (error)
+		goto fail_unlisten;
+
+	error = daemons_start();
+	if (error)
+		goto fail_unlisten;
+
+	atomic_set(&accepting, 1);
+
+	return 0;
+
+      fail_unlisten:
+	close_connection(connections[0], 0);
+	kmem_cache_free(con_cache, connections[0]);
+	kmem_cache_destroy(con_cache);
+
+      fail_free_conn:
+	kfree(connections);
+
+      out:
+	return error;
+}
+
+int dlm_lowcomms_init(void)
+{
+	INIT_LIST_HEAD(&read_sockets);
+	INIT_LIST_HEAD(&write_sockets);
+	INIT_LIST_HEAD(&state_sockets);
+
+	spin_lock_init(&read_sockets_lock);
+	spin_lock_init(&write_sockets_lock);
+	spin_lock_init(&state_sockets_lock);
+	init_MUTEX(&connections_lock);
+
+	return 0;
+}
+
+void dlm_lowcomms_exit(void)
+{
+}
+
+/*
+ * Overrides for Emacs so that we follow Linus's tabbing style.
+ * Emacs will notice this stuff at the end of the file and automatically
+ * adjust the settings for this buffer only.  This must remain at the end
+ * of the file.
+ * ---------------------------------------------------------------------------
+ * Local variables:
+ * c-file-style: "linux"
+ * End:
+ */