[DLM] The core of the DLM for GFS2/CLVM

This is the core of the distributed lock manager which is required
to use GFS2 as a cluster filesystem. It is also used by CLVM and
can be used as a standalone lock manager independantly of either
of these two projects.

It implements VAX-style locking modes.

Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Steve Whitehouse <swhiteho@redhat.com>

1 files changed, 1218 insertions, 0 deletions

diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
new file mode 100644
index 000000000000..09b0124f7fc4
--- /dev/null
+++ b/fs/dlm/lowcomms.c
@@ -0,0 +1,1218 @@
+/******************************************************************************
+*******************************************************************************
+**
+**  Copyright (C) Sistina Software, Inc.  1997-2003  All rights reserved.
+**  Copyright (C) 2004-2005 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 *local_addr[DLM_MAX_ADDR_COUNT];
+static int			local_count;
+static int			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;
+};
+
+static DEFINE_IDR(nodeinfo_idr);
+static struct rw_semaphore	nodeinfo_lock;
+static int			max_nodeid;
+
+struct cbuf {
+	unsigned		base;
+	unsigned		len;
+	unsigned		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;
+};
+
+/* 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;
+};
+
+#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_DATA(cb) (((cb)->base + (cb)->len) & (cb)->mask)
+
+#define CBUF_INIT(cb, size) \
+do { \
+	(cb)->base = (cb)->len = 0; \
+	(cb)->mask = ((size)-1); \
+} while(0)
+
+#define CBUF_EAT(cb, n) \
+do { \
+	(cb)->len  -= (n); \
+	(cb)->base += (n); \
+	(cb)->base &= (cb)->mask; \
+} while(0)
+
+
+/* List of nodes which have writes pending */
+static struct list_head write_nodes;
+static spinlock_t write_nodes_lock;
+
+/* Maximum number of incoming messages to process before
+ * doing a schedule()
+ */
+#define MAX_RX_MSG_COUNT 25
+
+/* Manage daemons */
+static struct task_struct *recv_task;
+static struct task_struct *send_task;
+static wait_queue_head_t lowcomms_recv_wait;
+static atomic_t accepting;
+
+/* The SCTP connection */
+static struct connection sctp_con;
+
+
+static int nodeid_to_addr(int nodeid, struct sockaddr *retaddr)
+{
+	struct sockaddr_storage addr;
+	int error;
+
+	if (!local_count)
+		return -1;
+
+	error = dlm_nodeid_to_addr(nodeid, &addr);
+	if (error)
+		return error;
+
+	if (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;
+}
+
+static struct nodeinfo *nodeid2nodeinfo(int nodeid, int 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) {
+		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);
+		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)
+{
+	atomic_inc(&sctp_con.waiting_requests);
+	if (test_and_set_bit(CF_READ_PENDING, &sctp_con.flags))
+		return;
+
+	wake_up_interruptible(&lowcomms_recv_wait);
+}
+
+
+/* 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 (!local_count)
+		return;
+
+	if (!port) {
+		if (local_addr[0]->ss_family == AF_INET) {
+			local4_addr = (struct sockaddr_in *)local_addr[0];
+			port = be16_to_cpu(local4_addr->sin_port);
+		} else {
+			local6_addr = (struct sockaddr_in6 *)local_addr[0];
+			port = be16_to_cpu(local6_addr->sin6_port);
+		}
+	}
+
+	saddr->ss_family = local_addr[0]->ss_family;
+	if (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 = (struct sctp_sndrcvinfo *)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);
+			}
+		}
+	}
+	wake_up_process(send_task);
+}
+
+/* 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 */
+			spin_lock(&ni->lock);
+			ni->assoc_id = sn->sn_assoc_change.sac_assoc_id;
+			spin_unlock(&ni->lock);
+
+			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);
+			}
+			wake_up_process(send_task);
+		}
+		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));
+
+	memset(incmsg, 0, sizeof(incmsg));
+	msg.msg_name = &msgname;
+	msg.msg_namelen = sizeof(msgname);
+	msg.msg_flags = 0;
+	msg.msg_control = incmsg;
+	msg.msg_controllen = sizeof(incmsg);
+
+	/* 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, 1, 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 = (struct sctp_sndrcvinfo *)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);
+			}
+			wake_up_process(send_task);
+		}
+	}
+
+	/* INIT sends a message with length of 1 - ignore it */
+	if (r == 1)
+		return 0;
+
+	CBUF_ADD(&sctp_con.cb, ret);
+	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;
+	schedule();
+	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.tcp_port, num);
+
+	return result;
+}
+
+static void init_local(void)
+{
+	struct sockaddr_storage sas, *addr;
+	int i;
+
+	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));
+		local_addr[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 (!local_count) {
+		init_local();
+		if (!local_count) {
+			log_print("no local IP address has been set");
+			goto out;
+		}
+	}
+
+	result = sock_create_kern(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 < local_count; i++) {
+		memcpy(&localaddr, local_addr[i], sizeof(localaddr));
+		make_sockaddr(&localaddr, dlm_config.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(int 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, int allocation, char **ppc)
+{
+	struct writequeue_entry *e;
+	int offset = 0;
+	int users = 0;
+	struct nodeinfo *ni;
+
+	if (!atomic_read(&accepting))
+		return NULL;
+
+	ni = nodeid2nodeinfo(nodeid, allocation);
+	if (!ni)
+		return NULL;
+
+	spin_lock(&ni->writequeue_lock);
+	e = list_entry(ni->writequeue.prev, struct writequeue_entry, list);
+	if (((struct list_head *) e == &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;
+
+	if (!atomic_read(&accepting))
+		return;
+
+	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);
+		wake_up_process(send_task);
+	}
+	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.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 = (struct sctp_sndrcvinfo *)CMSG_DATA(cmsg);
+	memset(sinfo, 0x00, sizeof(struct sctp_sndrcvinfo));
+	sinfo->sinfo_ppid = cpu_to_le32(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 int 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 0;
+	}
+	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 = (struct sctp_sndrcvinfo *)CMSG_DATA(cmsg);
+	memset(sinfo, 0x00, sizeof(struct sctp_sndrcvinfo));
+	sinfo->sinfo_ppid = cpu_to_le32(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);
+		kmap(e->page);
+		len = e->len;
+		offset = e->offset;
+		BUG_ON(len == 0 && e->users == 0);
+		spin_unlock(&ni->writequeue_lock);
+
+		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 */
+			schedule();
+		}
+
+		spin_lock(&ni->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(&ni->writequeue_lock);
+ out:
+	return ret;
+
+ 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 ret;
+}
+
+/* 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);
+		}
+	}
+}
+
+static int write_list_empty(void)
+{
+	int status;
+
+	spin_lock_bh(&write_nodes_lock);
+	status = list_empty(&write_nodes);
+	spin_unlock_bh(&write_nodes_lock);
+
+	return status;
+}
+
+static int dlm_recvd(void *data)
+{
+	DECLARE_WAITQUEUE(wait, current);
+
+	while (!kthread_should_stop()) {
+		int count = 0;
+
+		set_current_state(TASK_INTERRUPTIBLE);
+		add_wait_queue(&lowcomms_recv_wait, &wait);
+		if (!test_bit(CF_READ_PENDING, &sctp_con.flags))
+			schedule();
+		remove_wait_queue(&lowcomms_recv_wait, &wait);
+		set_current_state(TASK_RUNNING);
+
+		if (test_and_clear_bit(CF_READ_PENDING, &sctp_con.flags)) {
+			int ret;
+
+			do {
+				ret = receive_from_sock();
+
+				/* Don't starve out everyone else */
+				if (++count >= MAX_RX_MSG_COUNT) {
+					schedule();
+					count = 0;
+				}
+			} while (!kthread_should_stop() && ret >=0);
+		}
+		schedule();
+	}
+
+	return 0;
+}
+
+static int dlm_sendd(void *data)
+{
+	DECLARE_WAITQUEUE(wait, current);
+
+	add_wait_queue(sctp_con.sock->sk->sk_sleep, &wait);
+
+	while (!kthread_should_stop()) {
+		set_current_state(TASK_INTERRUPTIBLE);
+		if (write_list_empty())
+			schedule();
+		set_current_state(TASK_RUNNING);
+
+		if (sctp_con.eagain_flag) {
+			sctp_con.eagain_flag = 0;
+			refill_write_queue();
+		}
+		process_output_queue();
+	}
+
+	remove_wait_queue(sctp_con.sock->sk->sk_sleep, &wait);
+
+	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;
+}
+
+/*
+ * This is quite likely to sleep...
+ */
+int dlm_lowcomms_start(void)
+{
+	int error;
+
+	spin_lock_init(&write_nodes_lock);
+	INIT_LIST_HEAD(&write_nodes);
+	init_rwsem(&nodeinfo_lock);
+
+	error = init_sock();
+	if (error)
+		goto fail_sock;
+	error = daemons_start();
+	if (error)
+		goto fail_sock;
+	atomic_set(&accepting, 1);
+	return 0;
+
+ fail_sock:
+	close_connection();
+	return error;
+}
+
+/* Set all the activity flags to prevent any socket activity. */
+
+void dlm_lowcomms_stop(void)
+{
+	atomic_set(&accepting, 0);
+	sctp_con.flags = 0x7;
+	daemons_stop();
+	clean_writequeues();
+	close_connection();
+	dealloc_nodeinfo();
+	max_nodeid = 0;
+}
+
+int dlm_lowcomms_init(void)
+{
+	init_waitqueue_head(&lowcomms_recv_wait);
+	return 0;
+}
+
+void dlm_lowcomms_exit(void)
+{
+	int i;
+
+	for (i = 0; i < local_count; i++)
+		kfree(local_addr[i]);
+	local_count = 0;
+	local_nodeid = 0;
+}
+