lowcomms-sctp.c

/******************************************************************************
*******************************************************************************
**
**  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 (well, hardly ever) waits.
 *
 */

#include <asm/ioctls.h>
#include <net/sock.h>
#include <net/tcp.h>
#include <net/sctp/user.h>
#include <linux/pagemap.h>
#include <linux/socket.h>
#include <linux/idr.h>

#include "dlm_internal.h"
#include "lowcomms.h"
#include "config.h"
#include "midcomms.h"

static struct sockaddr_storage *dlm_local_addr[DLM_MAX_ADDR_COUNT];
static int			dlm_local_count;
static int			dlm_local_nodeid;

/* One of these per connected node */

#define NI_INIT_PENDING 1
#define NI_WRITE_PENDING 2

struct nodeinfo {
	spinlock_t		lock;
	sctp_assoc_t		assoc_id;
	unsigned long		flags;
	struct list_head	write_list; /* nodes with pending writes */
	struct list_head	writequeue; /* outgoing writequeue_entries */
	spinlock_t		writequeue_lock;
	int			nodeid;
	struct work_struct      swork; /* Send workqueue */
	struct work_struct      lwork; /* Locking workqueue */
};

static DEFINE_IDR(nodeinfo_idr);
static DECLARE_RWSEM(nodeinfo_lock);
static int max_nodeid;

struct cbuf {
	unsigned int base;
	unsigned int len;
	unsigned int mask;
};

/* Just the one of these, now. But this struct keeps
   the connection-specific variables together */

#define CF_READ_PENDING 1

struct connection {
	struct socket           *sock;
	unsigned long		flags;
	struct page             *rx_page;
	atomic_t		waiting_requests;
	struct cbuf		cb;
	int                     eagain_flag;
	struct work_struct      work; /* Send workqueue */
};

/* 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 nodeinfo         *ni;
};

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;
}

/* List of nodes which have writes pending */
static LIST_HEAD(write_nodes);
static DEFINE_SPINLOCK(write_nodes_lock);


/* Maximum number of incoming messages to process before
 * doing a schedule()
 */
#define MAX_RX_MSG_COUNT 25

/* Work queues */
static struct workqueue_struct *recv_workqueue;
static struct workqueue_struct *send_workqueue;
static struct workqueue_struct *lock_workqueue;

/* The SCTP connection */
static struct connection sctp_con;

static void process_send_sockets(struct work_struct *work);
static void process_recv_sockets(struct work_struct *work);
static void process_lock_request(struct work_struct *work);

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;
}

/* If alloc is 0 here we will not attempt to allocate a new
   nodeinfo struct */
static struct nodeinfo *nodeid2nodeinfo(int nodeid, gfp_t alloc)
{
	struct nodeinfo *ni;
	int r;
	int n;

	down_read(&nodeinfo_lock);
	ni = idr_find(&nodeinfo_idr, nodeid);
	up_read(&nodeinfo_lock);

	if (ni || !alloc)
		return ni;

	down_write(&nodeinfo_lock);

	ni = idr_find(&nodeinfo_idr, nodeid);
	if (ni)
		goto out_up;

	r = idr_pre_get(&nodeinfo_idr, alloc);
	if (!r)
		goto out_up;

	ni = kmalloc(sizeof(struct nodeinfo), alloc);
	if (!ni)
		goto out_up;

	r = idr_get_new_above(&nodeinfo_idr, ni, nodeid, &n);
	if (r) {
		kfree(ni);
		ni = NULL;
		goto out_up;
	}
	if (n != nodeid) {
		idr_remove(&nodeinfo_idr, n);
		kfree(ni);
		ni = NULL;
		goto out_up;
	}
	memset(ni, 0, sizeof(struct nodeinfo));
	spin_lock_init(&ni->lock);
	INIT_LIST_HEAD(&ni->writequeue);
	spin_lock_init(&ni->writequeue_lock);
	INIT_WORK(&ni->lwork, process_lock_request);
	INIT_WORK(&ni->swork, process_send_sockets);
	ni->nodeid = nodeid;

	if (nodeid > max_nodeid)
		max_nodeid = nodeid;
out_up:
	up_write(&nodeinfo_lock);

	return ni;
}

/* Don't call this too often... */
static struct nodeinfo *assoc2nodeinfo(sctp_assoc_t assoc)
{
	int i;
	struct nodeinfo *ni;

	for (i=1; i<=max_nodeid; i++) {
		ni = nodeid2nodeinfo(i, 0);
		if (ni && ni->assoc_id == assoc)
			return ni;
	}
	return NULL;
}

/* Data or notification available on socket */
static void lowcomms_data_ready(struct sock *sk, int count_unused)
{
	if (test_and_set_bit(CF_READ_PENDING, &sctp_con.flags))
		queue_work(recv_workqueue, &sctp_con.work);
}


/* Add the port number to an IP6 or 4 sockaddr and return the address length.
   Also padd out the struct with zeros to make comparisons meaningful */

static void make_sockaddr(struct sockaddr_storage *saddr, uint16_t port,
			  int *addr_len)
{
	struct sockaddr_in *local4_addr;
	struct sockaddr_in6 *local6_addr;

	if (!dlm_local_count)
		return;

	if (!port) {
		if (dlm_local_addr[0]->ss_family == AF_INET) {
			local4_addr = (struct sockaddr_in *)dlm_local_addr[0];
			port = be16_to_cpu(local4_addr->sin_port);
		} else {
			local6_addr = (struct sockaddr_in6 *)dlm_local_addr[0];
			port = be16_to_cpu(local6_addr->sin6_port);
		}
	}

	saddr->ss_family = dlm_local_addr[0]->ss_family;
	if (dlm_local_addr[0]->ss_family == AF_INET) {
		struct sockaddr_in *in4_addr = (struct sockaddr_in *)saddr;
		in4_addr->sin_port = cpu_to_be16(port);
		memset(&in4_addr->sin_zero, 0, sizeof(in4_addr->sin_zero));
		memset(in4_addr+1, 0, sizeof(struct sockaddr_storage) -
		       sizeof(struct sockaddr_in));
		*addr_len = sizeof(struct sockaddr_in);
	} else {
		struct sockaddr_in6 *in6_addr = (struct sockaddr_in6 *)saddr;
		in6_addr->sin6_port = cpu_to_be16(port);
		memset(in6_addr+1, 0, sizeof(struct sockaddr_storage) -
		       sizeof(struct sockaddr_in6));
		*addr_len = sizeof(struct sockaddr_in6);
	}
}

/* Close the connection and tidy up */
static void close_connection(void)
{
	if (sctp_con.sock) {
		sock_release(sctp_con.sock);
		sctp_con.sock = NULL;
	}

	if (sctp_con.rx_page) {
		__free_page(sctp_con.rx_page);
		sctp_con.rx_page = NULL;
	}
}

/* We only send shutdown messages to nodes that are not part of the cluster */
static void 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;

	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(sctp_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 init_failed(void)
{
	int i;
	struct nodeinfo *ni;

	for (i=1; i<=max_nodeid; i++) {
		ni = nodeid2nodeinfo(i, 0);
		if (!ni)
			continue;

		if (test_and_clear_bit(NI_INIT_PENDING, &ni->flags)) {
			ni->assoc_id = 0;
			if (!test_and_set_bit(NI_WRITE_PENDING, &ni->flags)) {
				spin_lock_bh(&write_nodes_lock);
				list_add_tail(&ni->write_list, &write_nodes);
				spin_unlock_bh(&write_nodes_lock);
				queue_work(send_workqueue, &ni->swork);
			}
		}
	}
}

/* Something happened to an association */
static void process_sctp_notification(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;
			mm_segment_t fs;
			int nodeid;
			int prim_len, ret;
			int addr_len;
			struct nodeinfo *ni;

			/* This seems to happen when we received a connection
			 * too early... or something...  anyway, it happens but
			 * we always seem to get a real message too, see
			 * receive_from_sock */

			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);
				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;

			fs = get_fs();
			set_fs(get_ds());
			ret = sctp_con.sock->ops->getsockopt(sctp_con.sock,
							     IPPROTO_SCTP,
							     SCTP_PRIMARY_ADDR,
							     (char*)&prim,
							     &prim_len);
			set_fs(fs);
			if (ret < 0) {
				struct nodeinfo *ni;

				log_print("getsockopt/sctp_primary_addr on "
					  "new assoc %d failed : %d",
					  (int)sn->sn_assoc_change.sac_assoc_id,
					  ret);

				/* Retry INIT later */
				ni = assoc2nodeinfo(sn->sn_assoc_change.sac_assoc_id);
				if (ni)
					clear_bit(NI_INIT_PENDING, &ni->flags);
				return;
			}
			make_sockaddr(&prim.ssp_addr, 0, &addr_len);
			if (dlm_addr_to_nodeid(&prim.ssp_addr, &nodeid)) {
				log_print("reject connect from unknown addr");
				send_shutdown(prim.ssp_assoc_id);
				return;
			}

			ni = nodeid2nodeinfo(nodeid, GFP_KERNEL);
			if (!ni)
				return;

			/* Save the assoc ID */
			ni->assoc_id = sn->sn_assoc_change.sac_assoc_id;

			log_print("got new/restarted association %d nodeid %d",
				  (int)sn->sn_assoc_change.sac_assoc_id, nodeid);

			/* Send any pending writes */
			clear_bit(NI_INIT_PENDING, &ni->flags);
			if (!test_and_set_bit(NI_WRITE_PENDING, &ni->flags)) {
				spin_lock_bh(&write_nodes_lock);
				list_add_tail(&ni->write_list, &write_nodes);
				spin_unlock_bh(&write_nodes_lock);
				queue_work(send_workqueue, &ni->swork);
			}
		}
		break;

		case SCTP_COMM_LOST:
		case SCTP_SHUTDOWN_COMP:
		{
			struct nodeinfo *ni;

			ni = assoc2nodeinfo(sn->sn_assoc_change.sac_assoc_id);
			if (ni) {
				spin_lock(&ni->lock);
				ni->assoc_id = 0;
				spin_unlock(&ni->lock);
			}
		}
		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");
			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(void)
{
	int ret = 0;
	struct msghdr msg;
	struct kvec iov[2];
	unsigned len;
	int r;
	struct sctp_sndrcvinfo *sinfo;
	struct cmsghdr *cmsg;
	struct nodeinfo *ni;

	/* These two are marginally too big for stack allocation, but this
	 * function is (currently) only called by dlm_recvd so static should be
	 * OK.
	 */
	static struct sockaddr_storage msgname;
	static char incmsg[CMSG_SPACE(sizeof(struct sctp_sndrcvinfo))];

	if (sctp_con.sock == NULL)
		goto out;

	if (sctp_con.rx_page == NULL) {
		/*
		 * This doesn't need to be atomic, but I think it should
		 * improve performance if it is.
		 */
		sctp_con.rx_page = alloc_page(GFP_ATOMIC);
		if (sctp_con.rx_page == NULL)
			goto out_resched;
		cbuf_init(&sctp_con.cb, PAGE_CACHE_SIZE);
	}

	memset(&incmsg, 0, sizeof(incmsg));
	memset(&msgname, 0, sizeof(msgname));

	msg.msg_name = &msgname;
	msg.msg_namelen = sizeof(msgname);
	msg.msg_flags = 0;
	msg.msg_control = incmsg;
	msg.msg_controllen = sizeof(incmsg);
	msg.msg_iovlen = 1;

	/* I don't see why this circular buffer stuff is necessary for SCTP
	 * which is a packet-based protocol, but the whole thing breaks under
	 * load without it! The overhead is minimal (and is in the TCP lowcomms
	 * anyway, of course) so I'll leave it in until I can figure out what's
	 * really happening.
	 */

	/*
	 * 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 = sctp_con.cb.base - cbuf_data(&sctp_con.cb);
	iov[0].iov_base = page_address(sctp_con.rx_page) +
		cbuf_data(&sctp_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(&sctp_con.cb) >= sctp_con.cb.base) {
		iov[0].iov_len = PAGE_CACHE_SIZE - cbuf_data(&sctp_con.cb);
		iov[1].iov_len = sctp_con.cb.base;
		iov[1].iov_base = page_address(sctp_con.rx_page);
		msg.msg_iovlen = 2;
	}
	len = iov[0].iov_len + iov[1].iov_len;

	r = ret = kernel_recvmsg(sctp_con.sock, &msg, iov, msg.msg_iovlen, len,
				 MSG_NOSIGNAL | MSG_DONTWAIT);
	if (ret <= 0)
		goto out_close;

	msg.msg_control = incmsg;
	msg.msg_controllen = sizeof(incmsg);
	cmsg = CMSG_FIRSTHDR(&msg);
	sinfo = CMSG_DATA(cmsg);

	if (msg.msg_flags & MSG_NOTIFICATION) {
		process_sctp_notification(&msg, page_address(sctp_con.rx_page));
		return 0;
	}

	/* Is this a new association ? */
	ni = nodeid2nodeinfo(le32_to_cpu(sinfo->sinfo_ppid), GFP_KERNEL);
	if (ni) {
		ni->assoc_id = sinfo->sinfo_assoc_id;
		if (test_and_clear_bit(NI_INIT_PENDING, &ni->flags)) {

			if (!test_and_set_bit(NI_WRITE_PENDING, &ni->flags)) {
				spin_lock_bh(&write_nodes_lock);
				list_add_tail(&ni->write_list, &write_nodes);
				spin_unlock_bh(&write_nodes_lock);
				queue_work(send_workqueue, &ni->swork);
			}
		}
	}

	/* INIT sends a message with length of 1 - ignore it */
	if (r == 1)
		return 0;

	cbuf_add(&sctp_con.cb, ret);
	// PJC: TODO: Add to node's workqueue....can we ??
	ret = dlm_process_incoming_buffer(cpu_to_le32(sinfo->sinfo_ppid),
					  page_address(sctp_con.rx_page),
					  sctp_con.cb.base, sctp_con.cb.len,
					  PAGE_CACHE_SIZE);
	if (ret < 0)
		goto out_close;
	cbuf_eat(&sctp_con.cb, ret);

out:
	ret = 0;
	goto out_ret;

out_resched:
	lowcomms_data_ready(sctp_con.sock->sk, 0);
	ret = 0;
	cond_resched();
	goto out_ret;

out_close:
	if (ret != -EAGAIN)
		log_print("error reading from sctp socket: %d", ret);
out_ret:
	return ret;
}

/* Bind to an IP address. SCTP allows multiple address so it can do multi-homing */
static int add_bind_addr(struct sockaddr_storage *addr, int addr_len, int num)
{
	mm_segment_t fs;
	int result = 0;

	fs = get_fs();
	set_fs(get_ds());
	if (num == 1)
		result = sctp_con.sock->ops->bind(sctp_con.sock,
						  (struct sockaddr *) addr,
						  addr_len);
	else
		result = sctp_con.sock->ops->setsockopt(sctp_con.sock, SOL_SCTP,
							SCTP_SOCKOPT_BINDX_ADD,
							(char *)addr, addr_len);
	set_fs(fs);

	if (result < 0)
		log_print("Can't bind to port %d addr number %d",
			  dlm_config.ci_tcp_port, num);

	return result;
}

static void init_local(void)
{
	struct sockaddr_storage sas, *addr;
	int i;

	dlm_local_nodeid = dlm_our_nodeid();

	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;
	}
}

/* Initialise SCTP socket and bind to all interfaces */
static int init_sock(void)
{
	mm_segment_t fs;
	struct socket *sock = NULL;
	struct sockaddr_storage localaddr;
	struct sctp_event_subscribe subscribe;
	int result = -EINVAL, num = 1, i, addr_len;

	if (!dlm_local_count) {
		init_local();
		if (!dlm_local_count) {
			log_print("no local IP address has been set");
			goto out;
		}
	}

	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;

	fs = get_fs();
	set_fs(get_ds());
	result = sock->ops->setsockopt(sock, SOL_SCTP, SCTP_EVENTS,
				       (char *)&subscribe, sizeof(subscribe));
	set_fs(fs);

	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 = &sctp_con;
	sctp_con.sock = sock;
	sctp_con.sock->sk->sk_data_ready = lowcomms_data_ready;

	/* 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_bind_addr(&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);
	sctp_con.sock = NULL;
out:
	return result;
}


static struct writequeue_entry *new_writequeue_entry(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;

	return entry;
}

void *dlm_lowcomms_get_buffer(int nodeid, int len, gfp_t allocation, char **ppc)
{
	struct writequeue_entry *e;
	int offset = 0;
	int users = 0;
	struct nodeinfo *ni;

	ni = nodeid2nodeinfo(nodeid, allocation);
	if (!ni)
		return NULL;

	spin_lock(&ni->writequeue_lock);
	e = list_entry(ni->writequeue.prev, struct writequeue_entry, list);
	if ((&e->list == &ni->writequeue) ||
	    (PAGE_CACHE_SIZE - e->end < len)) {
		e = NULL;
	} else {
		offset = e->end;
		e->end += len;
		users = e->users++;
	}
	spin_unlock(&ni->writequeue_lock);

	if (e) {
	got_one:
		if (users == 0)
			kmap(e->page);
		*ppc = page_address(e->page) + offset;
		return e;
	}

	e = new_writequeue_entry(allocation);
	if (e) {
		spin_lock(&ni->writequeue_lock);
		offset = e->end;
		e->end += len;
		e->ni = ni;
		users = e->users++;
		list_add_tail(&e->list, &ni->writequeue);
		spin_unlock(&ni->writequeue_lock);
		goto got_one;
	}
	return NULL;
}

void dlm_lowcomms_commit_buffer(void *arg)
{
	struct writequeue_entry *e = (struct writequeue_entry *) arg;
	int users;
	struct nodeinfo *ni = e->ni;

	spin_lock(&ni->writequeue_lock);
	users = --e->users;
	if (users)
		goto out;
	e->len = e->end - e->offset;
	kunmap(e->page);
	spin_unlock(&ni->writequeue_lock);

	if (!test_and_set_bit(NI_WRITE_PENDING, &ni->flags)) {
		spin_lock_bh(&write_nodes_lock);
		list_add_tail(&ni->write_list, &write_nodes);
		spin_unlock_bh(&write_nodes_lock);

		queue_work(send_workqueue, &ni->swork);
	}
	return;

out:
	spin_unlock(&ni->writequeue_lock);
	return;
}

static void free_entry(struct writequeue_entry *e)
{
	__free_page(e->page);
	kfree(e);
}

/* Initiate an SCTP association. In theory we could just use sendmsg() on
   the first IP address and it should work, but this allows us to set up the
   association before sending any valuable data that we can't afford to lose.
   It also keeps the send path clean as it can now always use the association ID */
static void initiate_association(int nodeid)
{
	struct sockaddr_storage rem_addr;
	static char outcmsg[CMSG_SPACE(sizeof(struct sctp_sndrcvinfo))];
	struct msghdr outmessage;
	struct cmsghdr *cmsg;
	struct sctp_sndrcvinfo *sinfo;
	int ret;
	int addrlen;
	char buf[1];
	struct kvec iov[1];
	struct nodeinfo *ni;

	log_print("Initiating association with node %d", nodeid);

	ni = nodeid2nodeinfo(nodeid, GFP_KERNEL);
	if (!ni)
		return;

	if (nodeid_to_addr(nodeid, (struct sockaddr *)&rem_addr)) {
		log_print("no address for nodeid %d", nodeid);
		return;
	}

	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;

	iov[0].iov_base = buf;
	iov[0].iov_len = 1;

	/* Real INIT messages seem to cause trouble. Just send a 1 byte message
	   we can afford to lose */
	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_local_nodeid);

	outmessage.msg_controllen = cmsg->cmsg_len;
	ret = kernel_sendmsg(sctp_con.sock, &outmessage, iov, 1, 1);
	if (ret < 0) {
		log_print("send INIT to node failed: %d", ret);
		/* Try again later */
		clear_bit(NI_INIT_PENDING, &ni->flags);
	}
}

/* Send a message */
static void send_to_sock(struct nodeinfo *ni)
{
	int ret = 0;
	struct writequeue_entry *e;
	int len, offset;
	struct msghdr outmsg;
	static char outcmsg[CMSG_SPACE(sizeof(struct sctp_sndrcvinfo))];
	struct cmsghdr *cmsg;
	struct sctp_sndrcvinfo *sinfo;
	struct kvec iov;

	/* See if we need to init an association before we start
	   sending precious messages */
	spin_lock(&ni->lock);
	if (!ni->assoc_id && !test_and_set_bit(NI_INIT_PENDING, &ni->flags)) {
		spin_unlock(&ni->lock);
		initiate_association(ni->nodeid);
		return;
	}
	spin_unlock(&ni->lock);

	outmsg.msg_name = NULL; /* We use assoc_id */
	outmsg.msg_namelen = 0;
	outmsg.msg_control = outcmsg;
	outmsg.msg_controllen = sizeof(outcmsg);
	outmsg.msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL | MSG_EOR;

	cmsg = CMSG_FIRSTHDR(&outmsg);
	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_local_nodeid);
	sinfo->sinfo_assoc_id = ni->assoc_id;
	outmsg.msg_controllen = cmsg->cmsg_len;

	spin_lock(&ni->writequeue_lock);
	for (;;) {
		if (list_empty(&ni->writequeue))
			break;
		e = list_entry(ni->writequeue.next, struct writequeue_entry,
			       list);
		len = e->len;
		offset = e->offset;
		BUG_ON(len == 0 && e->users == 0);
		spin_unlock(&ni->writequeue_lock);
		kmap(e->page);

		ret = 0;
		if (len) {
			iov.iov_base = page_address(e->page)+offset;
			iov.iov_len = len;

			ret = kernel_sendmsg(sctp_con.sock, &outmsg, &iov, 1,
					     len);
			if (ret == -EAGAIN) {
				sctp_con.eagain_flag = 1;
				goto out;
			} else if (ret < 0)
				goto send_error;
		} else {
			/* Don't starve people filling buffers */
			cond_resched();
		}

		spin_lock(&ni->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(&ni->writequeue_lock);
out:
	return;

send_error:
	log_print("Error sending to node %d %d", ni->nodeid, ret);
	spin_lock(&ni->lock);
	if (!test_and_set_bit(NI_INIT_PENDING, &ni->flags)) {
		ni->assoc_id = 0;
		spin_unlock(&ni->lock);
		initiate_association(ni->nodeid);
	} else
		spin_unlock(&ni->lock);

	return;
}

/* Try to send any messages that are pending */
static void process_output_queue(void)
{
	struct list_head *list;
	struct list_head *temp;

	spin_lock_bh(&write_nodes_lock);
	list_for_each_safe(list, temp, &write_nodes) {
		struct nodeinfo *ni =
			list_entry(list, struct nodeinfo, write_list);
		clear_bit(NI_WRITE_PENDING, &ni->flags);
		list_del(&ni->write_list);

		spin_unlock_bh(&write_nodes_lock);

		send_to_sock(ni);
		spin_lock_bh(&write_nodes_lock);
	}
	spin_unlock_bh(&write_nodes_lock);
}

/* Called after we've had -EAGAIN and been woken up */
static void refill_write_queue(void)
{
	int i;

	for (i=1; i<=max_nodeid; i++) {
		struct nodeinfo *ni = nodeid2nodeinfo(i, 0);

		if (ni) {
			if (!test_and_set_bit(NI_WRITE_PENDING, &ni->flags)) {
				spin_lock_bh(&write_nodes_lock);
				list_add_tail(&ni->write_list, &write_nodes);
				spin_unlock_bh(&write_nodes_lock);
			}
		}
	}
}

static void clean_one_writequeue(struct nodeinfo *ni)
{
	struct list_head *list;
	struct list_head *temp;

	spin_lock(&ni->writequeue_lock);
	list_for_each_safe(list, temp, &ni->writequeue) {
		struct writequeue_entry *e =
			list_entry(list, struct writequeue_entry, list);
		list_del(&e->list);
		free_entry(e);
	}
	spin_unlock(&ni->writequeue_lock);
}

static void clean_writequeues(void)
{
	int i;

	for (i=1; i<=max_nodeid; i++) {
		struct nodeinfo *ni = nodeid2nodeinfo(i, 0);
		if (ni)
			clean_one_writequeue(ni);
	}
}


static void dealloc_nodeinfo(void)
{
	int i;

	for (i=1; i<=max_nodeid; i++) {
		struct nodeinfo *ni = nodeid2nodeinfo(i, 0);
		if (ni) {
			idr_remove(&nodeinfo_idr, i);
			kfree(ni);
		}
	}
}

int dlm_lowcomms_close(int nodeid)
{
	struct nodeinfo *ni;

	ni = nodeid2nodeinfo(nodeid, 0);
	if (!ni)
		return -1;

	spin_lock(&ni->lock);
	if (ni->assoc_id) {
		ni->assoc_id = 0;
		/* Don't send shutdown here, sctp will just queue it
		   till the node comes back up! */
	}
	spin_unlock(&ni->lock);

	clean_one_writequeue(ni);
	clear_bit(NI_INIT_PENDING, &ni->flags);
	return 0;
}

// PJC: The work queue function for receiving.
static void process_recv_sockets(struct work_struct *work)
{
	if (test_and_clear_bit(CF_READ_PENDING, &sctp_con.flags)) {
		int ret;
		int count = 0;

		do {
			ret = receive_from_sock();

			/* Don't starve out everyone else */
			if (++count >= MAX_RX_MSG_COUNT) {
				cond_resched();
				count = 0;
			}
		} while (!kthread_should_stop() && ret >=0);
	}
	cond_resched();
}

// PJC: the work queue function for sending
static void process_send_sockets(struct work_struct *work)
{
	if (sctp_con.eagain_flag) {
		sctp_con.eagain_flag = 0;
		refill_write_queue();
	}
	process_output_queue();
}

// PJC: Process lock requests from a particular node.
// TODO: can we optimise this out on UP ??
static void process_lock_request(struct work_struct *work)
{
}

static void daemons_stop(void)
{
	destroy_workqueue(recv_workqueue);
	destroy_workqueue(send_workqueue);
	destroy_workqueue(lock_workqueue);
}

static int daemons_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;
	}

	lock_workqueue = create_workqueue("dlm_rlock");
	error = IS_ERR(lock_workqueue);
	if (error) {
		log_print("can't start dlm_rlock %d", error);
		destroy_workqueue(send_workqueue);
		destroy_workqueue(recv_workqueue);
		return error;
	}

	return 0;
}

/*
 * This is quite likely to sleep...
 */
int dlm_lowcomms_start(void)
{
	int error;

	INIT_WORK(&sctp_con.work, process_recv_sockets);

	error = init_sock();
	if (error)
		goto fail_sock;
	error = daemons_start();
	if (error)
		goto fail_sock;
	return 0;

fail_sock:
	close_connection();
	return error;
}

void dlm_lowcomms_stop(void)
{
	int i;

	sctp_con.flags = 0x7;
	daemons_stop();
	clean_writequeues();
	close_connection();
	dealloc_nodeinfo();
	max_nodeid = 0;

	dlm_local_count = 0;
	dlm_local_nodeid = 0;

	for (i = 0; i < dlm_local_count; i++)
		kfree(dlm_local_addr[i]);
}