// SPDX-License-Identifier: GPL-2.0-only
/******************************************************************************
*******************************************************************************
**
**  Copyright (C) Sistina Software, Inc.  1997-2003  All rights reserved.
**  Copyright (C) 2004-2009 Red Hat, Inc.  All rights reserved.
**
**
*******************************************************************************
******************************************************************************/

/*
 * lowcomms.c
 *
 * This is the "low-level" comms layer.
 *
 * It is responsible for sending/receiving messages
 * from other nodes in the cluster.
 *
 * Cluster nodes are referred to by their nodeids. nodeids are
 * simply 32 bit numbers to the locking module - if they need to
 * be expanded for the cluster infrastructure then that is its
 * responsibility. It is this layer's
 * responsibility to resolve these into IP address or
 * whatever it needs for inter-node communication.
 *
 * The comms level is two kernel threads that deal mainly with
 * the receiving of messages from other nodes and passing them
 * up to the mid-level comms layer (which understands the
 * message format) for execution by the locking core, and
 * a send thread which does all the setting up of connections
 * to remote nodes and the sending of data. Threads are not allowed
 * to send their own data because it may cause them to wait in times
 * of high load. Also, this way, the sending thread can collect together
 * messages bound for one node and send them in one block.
 *
 * lowcomms will choose to use either TCP or SCTP as its transport layer
 * depending on the configuration variable 'protocol'. This should be set
 * to 0 (default) for TCP or 1 for SCTP. It should be configured using a
 * cluster-wide mechanism as it must be the same on all nodes of the cluster
 * for the DLM to function.
 *
 */

#include <asm/ioctls.h>
#include <net/sock.h>
#include <net/tcp.h>
#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/mutex.h>
#include <linux/sctp.h>
#include <linux/slab.h>
#include <net/sctp/sctp.h>
#include <net/ipv6.h>

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

#define NEEDED_RMEM (4*1024*1024)
#define CONN_HASH_SIZE 32

/* Number of messages to send before rescheduling */
#define MAX_SEND_MSG_COUNT 25

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

static void cbuf_add(struct cbuf *cb, int n)
{
        cb->len += n;
}

static int cbuf_data(struct cbuf *cb)
{
        return ((cb->base + cb->len) & cb->mask);
}

static void cbuf_init(struct cbuf *cb, int size)
{
        cb->base = cb->len = 0;
        cb->mask = size-1;
}

static void cbuf_eat(struct cbuf *cb, int n)
{
        cb->len  -= n;
        cb->base += n;
        cb->base &= cb->mask;
}

static bool cbuf_empty(struct cbuf *cb)
{
        return cb->len == 0;
}

struct connection {
        struct socket *sock;    /* NULL if not connected */
        uint32_t nodeid;        /* So we know who we are in the list */
        struct mutex sock_mutex;
        unsigned long flags;
#define CF_READ_PENDING 1
#define CF_WRITE_PENDING 2
#define CF_INIT_PENDING 4
#define CF_IS_OTHERCON 5
#define CF_CLOSE 6
#define CF_APP_LIMITED 7
#define CF_CLOSING 8
        struct list_head writequeue;  /* List of outgoing writequeue_entries */
        spinlock_t writequeue_lock;
        int (*rx_action) (struct connection *); /* What to do when active */
        void (*connect_action) (struct connection *);   /* What to do to connect */
        struct page *rx_page;
        struct cbuf cb;
        int retries;
#define MAX_CONNECT_RETRIES 3
        struct hlist_node list;
        struct connection *othercon;
        struct work_struct rwork; /* Receive workqueue */
        struct work_struct swork; /* Send workqueue */
};
#define sock2con(x) ((struct connection *)(x)->sk_user_data)

/* An entry waiting to be sent */
struct writequeue_entry {
        struct list_head list;
        struct page *page;
        int offset;
        int len;
        int end;
        int users;
        struct connection *con;
};

struct dlm_node_addr {
        struct list_head list;
        int nodeid;
        int addr_count;
        int curr_addr_index;
        struct sockaddr_storage *addr[DLM_MAX_ADDR_COUNT];
};

static struct listen_sock_callbacks {
        void (*sk_error_report)(struct sock *);
        void (*sk_data_ready)(struct sock *);
        void (*sk_state_change)(struct sock *);
        void (*sk_write_space)(struct sock *);
} listen_sock;

static LIST_HEAD(dlm_node_addrs);
static DEFINE_SPINLOCK(dlm_node_addrs_spin);

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

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

static struct hlist_head connection_hash[CONN_HASH_SIZE];
static DEFINE_MUTEX(connections_lock);
static struct kmem_cache *con_cache;

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


/* This is deliberately very simple because most clusters have simple
   sequential nodeids, so we should be able to go straight to a connection
   struct in the array */
static inline int nodeid_hash(int nodeid)
{
        return nodeid & (CONN_HASH_SIZE-1);
}

static struct connection *__find_con(int nodeid)
{
        int r;
        struct connection *con;

        r = nodeid_hash(nodeid);

        hlist_for_each_entry(con, &connection_hash[r], list) {
                if (con->nodeid == nodeid)
                        return con;
        }
        return NULL;
}

/*
 * If 'allocation' is zero then we don't attempt to create a new
 * connection structure for this node.
 */
static struct connection *__nodeid2con(int nodeid, gfp_t alloc)
{
        struct connection *con = NULL;
        int r;

        con = __find_con(nodeid);
        if (con || !alloc)
                return con;

        con = kmem_cache_zalloc(con_cache, alloc);
        if (!con)
                return NULL;

        r = nodeid_hash(nodeid);
        hlist_add_head(&con->list, &connection_hash[r]);

        con->nodeid = nodeid;
        mutex_init(&con->sock_mutex);
        INIT_LIST_HEAD(&con->writequeue);
        spin_lock_init(&con->writequeue_lock);
        INIT_WORK(&con->swork, process_send_sockets);
        INIT_WORK(&con->rwork, process_recv_sockets);

        /* Setup action pointers for child sockets */
        if (con->nodeid) {
                struct connection *zerocon = __find_con(0);

                con->connect_action = zerocon->connect_action;
                if (!con->rx_action)
                        con->rx_action = zerocon->rx_action;
        }

        return con;
}

/* Loop round all connections */
static void foreach_conn(void (*conn_func)(struct connection *c))
{
        int i;
        struct hlist_node *n;
        struct connection *con;

        for (i = 0; i < CONN_HASH_SIZE; i++) {
                hlist_for_each_entry_safe(con, n, &connection_hash[i], list)
                        conn_func(con);
        }
}

static struct connection *nodeid2con(int nodeid, gfp_t allocation)
{
        struct connection *con;

        mutex_lock(&connections_lock);
        con = __nodeid2con(nodeid, allocation);
        mutex_unlock(&connections_lock);

        return con;
}

static struct dlm_node_addr *find_node_addr(int nodeid)
{
        struct dlm_node_addr *na;

        list_for_each_entry(na, &dlm_node_addrs, list) {
                if (na->nodeid == nodeid)
                        return na;
        }
        return NULL;
}

static int addr_compare(struct sockaddr_storage *x, struct sockaddr_storage *y)
{
        switch (x->ss_family) {
        case AF_INET: {
                struct sockaddr_in *sinx = (struct sockaddr_in *)x;
                struct sockaddr_in *siny = (struct sockaddr_in *)y;
                if (sinx->sin_addr.s_addr != siny->sin_addr.s_addr)
                        return 0;
                if (sinx->sin_port != siny->sin_port)
                        return 0;
                break;
        }
        case AF_INET6: {
                struct sockaddr_in6 *sinx = (struct sockaddr_in6 *)x;
                struct sockaddr_in6 *siny = (struct sockaddr_in6 *)y;
                if (!ipv6_addr_equal(&sinx->sin6_addr, &siny->sin6_addr))
                        return 0;
                if (sinx->sin6_port != siny->sin6_port)
                        return 0;
                break;
        }
        default:
                return 0;
        }
        return 1;
}

static int nodeid_to_addr(int nodeid, struct sockaddr_storage *sas_out,
                          struct sockaddr *sa_out, bool try_new_addr)
{
        struct sockaddr_storage sas;
        struct dlm_node_addr *na;

        if (!dlm_local_count)
                return -1;

        spin_lock(&dlm_node_addrs_spin);
        na = find_node_addr(nodeid);
        if (na && na->addr_count) {
                memcpy(&sas, na->addr[na->curr_addr_index],
                       sizeof(struct sockaddr_storage));

                if (try_new_addr) {
                        na->curr_addr_index++;
                        if (na->curr_addr_index == na->addr_count)
                                na->curr_addr_index = 0;
                }
        }
        spin_unlock(&dlm_node_addrs_spin);

        if (!na)
                return -EEXIST;

        if (!na->addr_count)
                return -ENOENT;

        if (sas_out)
                memcpy(sas_out, &sas, sizeof(struct sockaddr_storage));

        if (!sa_out)
                return 0;

        if (dlm_local_addr[0]->ss_family == AF_INET) {
                struct sockaddr_in *in4  = (struct sockaddr_in *) &sas;
                struct sockaddr_in *ret4 = (struct sockaddr_in *) sa_out;
                ret4->sin_addr.s_addr = in4->sin_addr.s_addr;
        } else {
                struct sockaddr_in6 *in6  = (struct sockaddr_in6 *) &sas;
                struct sockaddr_in6 *ret6 = (struct sockaddr_in6 *) sa_out;
                ret6->sin6_addr = in6->sin6_addr;
        }

        return 0;
}

static int addr_to_nodeid(struct sockaddr_storage *addr, int *nodeid)
{
        struct dlm_node_addr *na;
        int rv = -EEXIST;
        int addr_i;

        spin_lock(&dlm_node_addrs_spin);
        list_for_each_entry(na, &dlm_node_addrs, list) {
                if (!na->addr_count)
                        continue;

                for (addr_i = 0; addr_i < na->addr_count; addr_i++) {
                        if (addr_compare(na->addr[addr_i], addr)) {
                                *nodeid = na->nodeid;
                                rv = 0;
                                goto unlock;
                        }
                }
        }
unlock:
        spin_unlock(&dlm_node_addrs_spin);
        return rv;
}

int dlm_lowcomms_addr(int nodeid, struct sockaddr_storage *addr, int len)
{
        struct sockaddr_storage *new_addr;
        struct dlm_node_addr *new_node, *na;

        new_node = kzalloc(sizeof(struct dlm_node_addr), GFP_NOFS);
        if (!new_node)
                return -ENOMEM;

        new_addr = kzalloc(sizeof(struct sockaddr_storage), GFP_NOFS);
        if (!new_addr) {
                kfree(new_node);
                return -ENOMEM;
        }

        memcpy(new_addr, addr, len);

        spin_lock(&dlm_node_addrs_spin);
        na = find_node_addr(nodeid);
        if (!na) {
                new_node->nodeid = nodeid;
                new_node->addr[0] = new_addr;
                new_node->addr_count = 1;
                list_add(&new_node->list, &dlm_node_addrs);
                spin_unlock(&dlm_node_addrs_spin);
                return 0;
        }

        if (na->addr_count >= DLM_MAX_ADDR_COUNT) {
                spin_unlock(&dlm_node_addrs_spin);
                kfree(new_addr);
                kfree(new_node);
                return -ENOSPC;
        }

        na->addr[na->addr_count++] = new_addr;
        spin_unlock(&dlm_node_addrs_spin);
        kfree(new_node);
        return 0;
}

/* Data available on socket or listen socket received a connect */
static void lowcomms_data_ready(struct sock *sk)
{
        struct connection *con;

        read_lock_bh(&sk->sk_callback_lock);
        con = sock2con(sk);
        if (con && !test_and_set_bit(CF_READ_PENDING, &con->flags))
                queue_work(recv_workqueue, &con->rwork);
        read_unlock_bh(&sk->sk_callback_lock);
}

static void lowcomms_write_space(struct sock *sk)
{
        struct connection *con;

        read_lock_bh(&sk->sk_callback_lock);
        con = sock2con(sk);
        if (!con)
                goto out;

        clear_bit(SOCK_NOSPACE, &con->sock->flags);

        if (test_and_clear_bit(CF_APP_LIMITED, &con->flags)) {
                con->sock->sk->sk_write_pending--;
                clear_bit(SOCKWQ_ASYNC_NOSPACE, &con->sock->flags);
        }

        queue_work(send_workqueue, &con->swork);
out:
        read_unlock_bh(&sk->sk_callback_lock);
}

static inline void lowcomms_connect_sock(struct connection *con)
{
        if (test_bit(CF_CLOSE, &con->flags))
                return;
        queue_work(send_workqueue, &con->swork);
        cond_resched();
}

static void lowcomms_state_change(struct sock *sk)
{
        /* SCTP layer is not calling sk_data_ready when the connection
         * is done, so we catch the signal through here. Also, it
         * doesn't switch socket state when entering shutdown, so we
         * skip the write in that case.
         */
        if (sk->sk_shutdown) {
                if (sk->sk_shutdown == RCV_SHUTDOWN)
                        lowcomms_data_ready(sk);
        } else if (sk->sk_state == TCP_ESTABLISHED) {
                lowcomms_write_space(sk);
        }
}

int dlm_lowcomms_connect_node(int nodeid)
{
        struct connection *con;

        if (nodeid == dlm_our_nodeid())
                return 0;

        con = nodeid2con(nodeid, GFP_NOFS);
        if (!con)
                return -ENOMEM;
        lowcomms_connect_sock(con);
        return 0;
}

static void lowcomms_error_report(struct sock *sk)
{
        struct connection *con;
        struct sockaddr_storage saddr;
        void (*orig_report)(struct sock *) = NULL;

        read_lock_bh(&sk->sk_callback_lock);
        con = sock2con(sk);
        if (con == NULL)
                goto out;

        orig_report = listen_sock.sk_error_report;
        if (con->sock == NULL ||
            kernel_getpeername(con->sock, (struct sockaddr *)&saddr) < 0) {
                printk_ratelimited(KERN_ERR "dlm: node %d: socket error "
                                   "sending to node %d, port %d, "
                                   "sk_err=%d/%d\n", dlm_our_nodeid(),
                                   con->nodeid, dlm_config.ci_tcp_port,
                                   sk->sk_err, sk->sk_err_soft);
        } else if (saddr.ss_family == AF_INET) {
                struct sockaddr_in *sin4 = (struct sockaddr_in *)&saddr;

                printk_ratelimited(KERN_ERR "dlm: node %d: socket error "
                                   "sending to node %d at %pI4, port %d, "
                                   "sk_err=%d/%d\n", dlm_our_nodeid(),
                                   con->nodeid, &sin4->sin_addr.s_addr,
                                   dlm_config.ci_tcp_port, sk->sk_err,
                                   sk->sk_err_soft);
        } else {
                struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)&saddr;

                printk_ratelimited(KERN_ERR "dlm: node %d: socket error "
                                   "sending to node %d at %u.%u.%u.%u, "
                                   "port %d, sk_err=%d/%d\n", dlm_our_nodeid(),
                                   con->nodeid, sin6->sin6_addr.s6_addr32[0],
                                   sin6->sin6_addr.s6_addr32[1],
                                   sin6->sin6_addr.s6_addr32[2],
                                   sin6->sin6_addr.s6_addr32[3],
                                   dlm_config.ci_tcp_port, sk->sk_err,
                                   sk->sk_err_soft);
        }
out:
        read_unlock_bh(&sk->sk_callback_lock);
        if (orig_report)
                orig_report(sk);
}

/* Note: sk_callback_lock must be locked before calling this function. */
static void save_listen_callbacks(struct socket *sock)
{
        struct sock *sk = sock->sk;

        listen_sock.sk_data_ready = sk->sk_data_ready;
        listen_sock.sk_state_change = sk->sk_state_change;
        listen_sock.sk_write_space = sk->sk_write_space;
        listen_sock.sk_error_report = sk->sk_error_report;
}

static void restore_callbacks(struct socket *sock)
{
        struct sock *sk = sock->sk;

        write_lock_bh(&sk->sk_callback_lock);
        sk->sk_user_data = NULL;
        sk->sk_data_ready = listen_sock.sk_data_ready;
        sk->sk_state_change = listen_sock.sk_state_change;
        sk->sk_write_space = listen_sock.sk_write_space;
        sk->sk_error_report = listen_sock.sk_error_report;
        write_unlock_bh(&sk->sk_callback_lock);
}

/* Make a socket active */
static void add_sock(struct socket *sock, struct connection *con)
{
        struct sock *sk = sock->sk;

        write_lock_bh(&sk->sk_callback_lock);
        con->sock = sock;

        sk->sk_user_data = con;
        /* Install a data_ready callback */
        sk->sk_data_ready = lowcomms_data_ready;
        sk->sk_write_space = lowcomms_write_space;
        sk->sk_state_change = lowcomms_state_change;
        sk->sk_allocation = GFP_NOFS;
        sk->sk_error_report = lowcomms_error_report;
        write_unlock_bh(&sk->sk_callback_lock);
}

/* Add the port number to an IPv6 or 4 sockaddr and return the address
   length */
static void make_sockaddr(struct sockaddr_storage *saddr, uint16_t port,
                          int *addr_len)
{
        saddr->ss_family =  dlm_local_addr[0]->ss_family;
        if (saddr->ss_family == AF_INET) {
                struct sockaddr_in *in4_addr = (struct sockaddr_in *)saddr;
                in4_addr->sin_port = cpu_to_be16(port);
                *addr_len = sizeof(struct sockaddr_in);
                memset(&in4_addr->sin_zero, 0, sizeof(in4_addr->sin_zero));
        } else {
                struct sockaddr_in6 *in6_addr = (struct sockaddr_in6 *)saddr;
                in6_addr->sin6_port = cpu_to_be16(port);
                *addr_len = sizeof(struct sockaddr_in6);
        }
        memset((char *)saddr + *addr_len, 0, sizeof(struct sockaddr_storage) - *addr_len);
}

/* Close a remote connection and tidy up */
static void close_connection(struct connection *con, bool and_other,
                             bool tx, bool rx)
{
        bool closing = test_and_set_bit(CF_CLOSING, &con->flags);

        if (tx && !closing && cancel_work_sync(&con->swork)) {
                log_print("canceled swork for node %d", con->nodeid);
                clear_bit(CF_WRITE_PENDING, &con->flags);
        }
        if (rx && !closing && cancel_work_sync(&con->rwork)) {
                log_print("canceled rwork for node %d", con->nodeid);
                clear_bit(CF_READ_PENDING, &con->flags);
        }

        mutex_lock(&con->sock_mutex);
        if (con->sock) {
                restore_callbacks(con->sock);
                sock_release(con->sock);
                con->sock = NULL;
        }
        if (con->othercon && and_other) {
                /* Will only re-enter once. */
                close_connection(con->othercon, false, true, true);
        }
        if (con->rx_page) {
                __free_page(con->rx_page);
                con->rx_page = NULL;
        }

        con->retries = 0;
        mutex_unlock(&con->sock_mutex);
        clear_bit(CF_CLOSING, &con->flags);
}

/* Data received from remote end */
static int receive_from_sock(struct connection *con)
{
        int ret = 0;
        struct msghdr msg = {};
        struct kvec iov[2];
        unsigned len;
        int r;
        int call_again_soon = 0;
        int nvec;

        mutex_lock(&con->sock_mutex);

        if (con->sock == NULL) {
                ret = -EAGAIN;
                goto out_close;
        }
        if (con->nodeid == 0) {
                ret = -EINVAL;
                goto out_close;
        }

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

        /*
         * iov[0] is the bit of the circular buffer between the current end
         * point (cb.base + cb.len) and the end of the buffer.
         */
        iov[0].iov_len = con->cb.base - cbuf_data(&con->cb);
        iov[0].iov_base = page_address(con->rx_page) + cbuf_data(&con->cb);
        iov[1].iov_len = 0;
        nvec = 1;

        /*
         * iov[1] is the bit of the circular buffer between the start of the
         * buffer and the start of the currently used section (cb.base)
         */
        if (cbuf_data(&con->cb) >= con->cb.base) {
                iov[0].iov_len = PAGE_SIZE - cbuf_data(&con->cb);
                iov[1].iov_len = con->cb.base;
                iov[1].iov_base = page_address(con->rx_page);
                nvec = 2;
        }
        len = iov[0].iov_len + iov[1].iov_len;
        iov_iter_kvec(&msg.msg_iter, READ, iov, nvec, len);

        r = ret = sock_recvmsg(con->sock, &msg, MSG_DONTWAIT | MSG_NOSIGNAL);
        if (ret <= 0)
                goto out_close;
        else if (ret == len)
                call_again_soon = 1;

        cbuf_add(&con->cb, ret);
        ret = dlm_process_incoming_buffer(con->nodeid,
                                          page_address(con->rx_page),
                                          con->cb.base, con->cb.len,
                                          PAGE_SIZE);
        if (ret == -EBADMSG) {
                log_print("lowcomms: addr=%p, base=%u, len=%u, read=%d",
                          page_address(con->rx_page), con->cb.base,
                          con->cb.len, r);
        }
        if (ret < 0)
                goto out_close;
        cbuf_eat(&con->cb, ret);

        if (cbuf_empty(&con->cb) && !call_again_soon) {
                __free_page(con->rx_page);
                con->rx_page = NULL;
        }

        if (call_again_soon)
                goto out_resched;
        mutex_unlock(&con->sock_mutex);
        return 0;

out_resched:
        if (!test_and_set_bit(CF_READ_PENDING, &con->flags))
                queue_work(recv_workqueue, &con->rwork);
        mutex_unlock(&con->sock_mutex);
        return -EAGAIN;

out_close:
        mutex_unlock(&con->sock_mutex);
        if (ret != -EAGAIN) {
                close_connection(con, true, true, false);
                /* Reconnect when there is something to send */
        }
        /* Don't return success if we really got EOF */
        if (ret == 0)
                ret = -EAGAIN;

        return ret;
}

/* Listening socket is busy, accept a connection */
static int accept_from_sock(struct connection *con)
{
        int result;
        struct sockaddr_storage peeraddr;
        struct socket *newsock;
        int len;
        int nodeid;
        struct connection *newcon;
        struct connection *addcon;

        mutex_lock(&connections_lock);
        if (!dlm_allow_conn) {
                mutex_unlock(&connections_lock);
                return -1;
        }
        mutex_unlock(&connections_lock);

        mutex_lock_nested(&con->sock_mutex, 0);

        if (!con->sock) {
                mutex_unlock(&con->sock_mutex);
                return -ENOTCONN;
        }

        result = kernel_accept(con->sock, &newsock, O_NONBLOCK);
        if (result < 0)
                goto accept_err;

        /* Get the connected socket's peer */
        memset(&peeraddr, 0, sizeof(peeraddr));
        len = newsock->ops->getname(newsock, (struct sockaddr *)&peeraddr, 2);
        if (len < 0) {
                result = -ECONNABORTED;
                goto accept_err;
        }

        /* Get the new node's NODEID */
        make_sockaddr(&peeraddr, 0, &len);
        if (addr_to_nodeid(&peeraddr, &nodeid)) {
                unsigned char *b=(unsigned char *)&peeraddr;
                log_print("connect from non cluster node");
                print_hex_dump_bytes("ss: ", DUMP_PREFIX_NONE, 
                                     b, sizeof(struct sockaddr_storage));
                sock_release(newsock);
                mutex_unlock(&con->sock_mutex);
                return -1;
        }

        log_print("got connection from %d", nodeid);

        /*  Check to see if we already have a connection to this node. This
         *  could happen if the two nodes initiate a connection at roughly
         *  the same time and the connections cross on the wire.
         *  In this case we store the incoming one in "othercon"
         */
        newcon = nodeid2con(nodeid, GFP_NOFS);
        if (!newcon) {
                result = -ENOMEM;
                goto accept_err;
        }
        mutex_lock_nested(&newcon->sock_mutex, 1);
        if (newcon->sock) {
                struct connection *othercon = newcon->othercon;

                if (!othercon) {
                        othercon = kmem_cache_zalloc(con_cache, GFP_NOFS);
                        if (!othercon) {
                                log_print("failed to allocate incoming socket");
                                mutex_unlock(&newcon->sock_mutex);
                                result = -ENOMEM;
                                goto accept_err;
                        }
                        othercon->nodeid = nodeid;
                        othercon->rx_action = receive_from_sock;
                        mutex_init(&othercon->sock_mutex);
                        INIT_LIST_HEAD(&othercon->writequeue);
                        spin_lock_init(&othercon->writequeue_lock);
                        INIT_WORK(&othercon->swork, process_send_sockets);
                        INIT_WORK(&othercon->rwork, process_recv_sockets);
                        set_bit(CF_IS_OTHERCON, &othercon->flags);
                }
                mutex_lock_nested(&othercon->sock_mutex, 2);
                if (!othercon->sock) {
                        newcon->othercon = othercon;
                        add_sock(newsock, othercon);
                        addcon = othercon;
                        mutex_unlock(&othercon->sock_mutex);
                }
                else {
                        printk("Extra connection from node %d attempted\n", nodeid);
                        result = -EAGAIN;
                        mutex_unlock(&othercon->sock_mutex);
                        mutex_unlock(&newcon->sock_mutex);
                        goto accept_err;
                }
        }
        else {
                newcon->rx_action = receive_from_sock;
                /* accept copies the sk after we've saved the callbacks, so we
                   don't want to save them a second time or comm errors will
                   result in calling sk_error_report recursively. */
                add_sock(newsock, newcon);
                addcon = newcon;
        }

        mutex_unlock(&newcon->sock_mutex);

        /*
         * Add it to the active queue in case we got data
         * between processing the accept adding the socket
         * to the read_sockets list
         */
        if (!test_and_set_bit(CF_READ_PENDING, &addcon->flags))
                queue_work(recv_workqueue, &addcon->rwork);
        mutex_unlock(&con->sock_mutex);

        return 0;

accept_err:
        mutex_unlock(&con->sock_mutex);
        if (newsock)
                sock_release(newsock);

        if (result != -EAGAIN)
                log_print("error accepting connection from node: %d", result);
        return result;
}

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

/*
 * writequeue_entry_complete - try to delete and free write queue entry
 * @e: write queue entry to try to delete
 * @completed: bytes completed
 *
 * writequeue_lock must be held.
 */
static void writequeue_entry_complete(struct writequeue_entry *e, int completed)
{
        e->offset += completed;
        e->len -= completed;

        if (e->len == 0 && e->users == 0) {
                list_del(&e->list);
                free_entry(e);
        }
}

/*
 * sctp_bind_addrs - bind a SCTP socket to all our addresses
 */
static int sctp_bind_addrs(struct connection *con, uint16_t port)
{
        struct sockaddr_storage localaddr;
        struct sockaddr *addr = (struct sockaddr *)&localaddr;
        int i, addr_len, result = 0;

        for (i = 0; i < dlm_local_count; i++) {
                memcpy(&localaddr, dlm_local_addr[i], sizeof(localaddr));
                make_sockaddr(&localaddr, port, &addr_len);

                if (!i)
                        result = kernel_bind(con->sock, addr, addr_len);
                else
                        result = sock_bind_add(con->sock->sk, addr, addr_len);

                if (result < 0) {
                        log_print("Can't bind to %d addr number %d, %d.\n",
                                  port, i + 1, result);
                        break;
                }
        }
        return result;
}

/* Initiate an SCTP association.
   This is a special case of send_to_sock() in that we don't yet have a
   peeled-off socket for this association, so we use the listening socket
   and add the primary IP address of the remote node.
 */
static void sctp_connect_to_sock(struct connection *con)
{
        struct sockaddr_storage daddr;
        int result;
        int addr_len;
        struct socket *sock;

        if (con->nodeid == 0) {
                log_print("attempt to connect sock 0 foiled");
                return;
        }

        mutex_lock(&con->sock_mutex);

        /* Some odd races can cause double-connects, ignore them */
        if (con->retries++ > MAX_CONNECT_RETRIES)
                goto out;

        if (con->sock) {
                log_print("node %d already connected.", con->nodeid);
                goto out;
        }

        memset(&daddr, 0, sizeof(daddr));
        result = nodeid_to_addr(con->nodeid, &daddr, NULL, true);
        if (result < 0) {
                log_print("no address for nodeid %d", con->nodeid);
                goto out;
        }

        /* Create a socket to communicate with */
        result = sock_create_kern(&init_net, dlm_local_addr[0]->ss_family,
                                  SOCK_STREAM, IPPROTO_SCTP, &sock);
        if (result < 0)
                goto socket_err;

        con->rx_action = receive_from_sock;
        con->connect_action = sctp_connect_to_sock;
        add_sock(sock, con);

        /* Bind to all addresses. */
        if (sctp_bind_addrs(con, 0))
                goto bind_err;

        make_sockaddr(&daddr, dlm_config.ci_tcp_port, &addr_len);

        log_print("connecting to %d", con->nodeid);

        /* Turn off Nagle's algorithm */
        sctp_sock_set_nodelay(sock->sk);

        /*
         * Make sock->ops->connect() function return in specified time,
         * since O_NONBLOCK argument in connect() function does not work here,
         * then, we should restore the default value of this attribute.
         */
        sock_set_sndtimeo(sock->sk, 5);
        result = sock->ops->connect(sock, (struct sockaddr *)&daddr, addr_len,
                                   0);
        sock_set_sndtimeo(sock->sk, 0);

        if (result == -EINPROGRESS)
                result = 0;
        if (result == 0)
                goto out;

bind_err:
        con->sock = NULL;
        sock_release(sock);

socket_err:
        /*
         * Some errors are fatal and this list might need adjusting. For other
         * errors we try again until the max number of retries is reached.
         */
        if (result != -EHOSTUNREACH &&
            result != -ENETUNREACH &&
            result != -ENETDOWN &&
            result != -EINVAL &&
            result != -EPROTONOSUPPORT) {
                log_print("connect %d try %d error %d", con->nodeid,
                          con->retries, result);
                mutex_unlock(&con->sock_mutex);
                msleep(1000);
                lowcomms_connect_sock(con);
                return;
        }

out:
        mutex_unlock(&con->sock_mutex);

}

/* Connect a new socket to its peer */
static void tcp_connect_to_sock(struct connection *con)
{
        struct sockaddr_storage saddr, src_addr;
        int addr_len;
        struct socket *sock = NULL;
        int result;

        if (con->nodeid == 0) {
                log_print("attempt to connect sock 0 foiled");
                return;
        }

        mutex_lock(&con->sock_mutex);
        if (con->retries++ > MAX_CONNECT_RETRIES)
                goto out;

        /* Some odd races can cause double-connects, ignore them */
        if (con->sock)
                goto out;

        /* Create a socket to communicate with */
        result = sock_create_kern(&init_net, dlm_local_addr[0]->ss_family,
                                  SOCK_STREAM, IPPROTO_TCP, &sock);
        if (result < 0)
                goto out_err;

        memset(&saddr, 0, sizeof(saddr));
        result = nodeid_to_addr(con->nodeid, &saddr, NULL, false);
        if (result < 0) {
                log_print("no address for nodeid %d", con->nodeid);
                goto out_err;
        }

        con->rx_action = receive_from_sock;
        con->connect_action = tcp_connect_to_sock;
        add_sock(sock, con);

        /* Bind to our cluster-known address connecting to avoid
           routing problems */
        memcpy(&src_addr, dlm_local_addr[0], sizeof(src_addr));
        make_sockaddr(&src_addr, 0, &addr_len);
        result = sock->ops->bind(sock, (struct sockaddr *) &src_addr,
                                 addr_len);
        if (result < 0) {
                log_print("could not bind for connect: %d", result);
                /* This *may* not indicate a critical error */
        }

        make_sockaddr(&saddr, dlm_config.ci_tcp_port, &addr_len);

        log_print("connecting to %d", con->nodeid);

        /* Turn off Nagle's algorithm */
        tcp_sock_set_nodelay(sock->sk);

        result = sock->ops->connect(sock, (struct sockaddr *)&saddr, addr_len,
                                   O_NONBLOCK);
        if (result == -EINPROGRESS)
                result = 0;
        if (result == 0)
                goto out;

out_err:
        if (con->sock) {
                sock_release(con->sock);
                con->sock = NULL;
        } else if (sock) {
                sock_release(sock);
        }
        /*
         * Some errors are fatal and this list might need adjusting. For other
         * errors we try again until the max number of retries is reached.
         */
        if (result != -EHOSTUNREACH &&
            result != -ENETUNREACH &&
            result != -ENETDOWN && 
            result != -EINVAL &&
            result != -EPROTONOSUPPORT) {
                log_print("connect %d try %d error %d", con->nodeid,
                          con->retries, result);
                mutex_unlock(&con->sock_mutex);
                msleep(1000);
                lowcomms_connect_sock(con);
                return;
        }
out:
        mutex_unlock(&con->sock_mutex);
        return;
}

static struct socket *tcp_create_listen_sock(struct connection *con,
                                             struct sockaddr_storage *saddr)
{
        struct socket *sock = NULL;
        int result = 0;
        int addr_len;

        if (dlm_local_addr[0]->ss_family == AF_INET)
                addr_len = sizeof(struct sockaddr_in);
        else
                addr_len = sizeof(struct sockaddr_in6);

        /* Create a socket to communicate with */
        result = sock_create_kern(&init_net, dlm_local_addr[0]->ss_family,
                                  SOCK_STREAM, IPPROTO_TCP, &sock);
        if (result < 0) {
                log_print("Can't create listening comms socket");
                goto create_out;
        }

        /* Turn off Nagle's algorithm */
        tcp_sock_set_nodelay(sock->sk);

        sock_set_reuseaddr(sock->sk);

        write_lock_bh(&sock->sk->sk_callback_lock);
        sock->sk->sk_user_data = con;
        save_listen_callbacks(sock);
        con->rx_action = accept_from_sock;
        con->connect_action = tcp_connect_to_sock;
        write_unlock_bh(&sock->sk->sk_callback_lock);

        /* Bind to our port */
        make_sockaddr(saddr, dlm_config.ci_tcp_port, &addr_len);
        result = sock->ops->bind(sock, (struct sockaddr *) saddr, addr_len);
        if (result < 0) {
                log_print("Can't bind to port %d", dlm_config.ci_tcp_port);
                sock_release(sock);
                sock = NULL;
                con->sock = NULL;
                goto create_out;
        }
        sock_set_keepalive(sock->sk);

        result = sock->ops->listen(sock, 5);
        if (result < 0) {
                log_print("Can't listen on port %d", dlm_config.ci_tcp_port);
                sock_release(sock);
                sock = NULL;
                goto create_out;
        }

create_out:
        return sock;
}

/* Get local addresses */
static void init_local(void)
{
        struct sockaddr_storage sas, *addr;
        int i;

        dlm_local_count = 0;
        for (i = 0; i < DLM_MAX_ADDR_COUNT; i++) {
                if (dlm_our_addr(&sas, i))
                        break;

                addr = kmemdup(&sas, sizeof(*addr), GFP_NOFS);
                if (!addr)
                        break;
                dlm_local_addr[dlm_local_count++] = addr;
        }
}

/* Initialise SCTP socket and bind to all interfaces */
static int sctp_listen_for_all(void)
{
        struct socket *sock = NULL;
        int result = -EINVAL;
        struct connection *con = nodeid2con(0, GFP_NOFS);

        if (!con)
                return -ENOMEM;

        log_print("Using SCTP for communications");

        result = sock_create_kern(&init_net, dlm_local_addr[0]->ss_family,
                                  SOCK_STREAM, IPPROTO_SCTP, &sock);
        if (result < 0) {
                log_print("Can't create comms socket, check SCTP is loaded");
                goto out;
        }

        sock_set_rcvbuf(sock->sk, NEEDED_RMEM);
        sctp_sock_set_nodelay(sock->sk);

        write_lock_bh(&sock->sk->sk_callback_lock);
        /* Init con struct */
        sock->sk->sk_user_data = con;
        save_listen_callbacks(sock);
        con->sock = sock;
        con->sock->sk->sk_data_ready = lowcomms_data_ready;
        con->rx_action = accept_from_sock;
        con->connect_action = sctp_connect_to_sock;

        write_unlock_bh(&sock->sk->sk_callback_lock);

        /* Bind to all addresses. */
        if (sctp_bind_addrs(con, dlm_config.ci_tcp_port))
                goto create_delsock;

        result = sock->ops->listen(sock, 5);
        if (result < 0) {
                log_print("Can't set socket listening");
                goto create_delsock;
        }

        return 0;

create_delsock:
        sock_release(sock);
        con->sock = NULL;
out:
        return result;
}

static int tcp_listen_for_all(void)
{
        struct socket *sock = NULL;
        struct connection *con = nodeid2con(0, GFP_NOFS);
        int result = -EINVAL;

        if (!con)
                return -ENOMEM;

        /* We don't support multi-homed hosts */
        if (dlm_local_addr[1] != NULL) {
                log_print("TCP protocol can't handle multi-homed hosts, "
                          "try SCTP");
                return -EINVAL;
        }

        log_print("Using TCP for communications");

        sock = tcp_create_listen_sock(con, dlm_local_addr[0]);
        if (sock) {
                add_sock(sock, con);
                result = 0;
        }
        else {
                result = -EADDRINUSE;
        }

        return result;
}



static struct writequeue_entry *new_writequeue_entry(struct connection *con,
                                                     gfp_t allocation)
{
        struct writequeue_entry *entry;

        entry = kmalloc(sizeof(struct writequeue_entry), allocation);
        if (!entry)
                return NULL;

        entry->page = alloc_page(allocation);
        if (!entry->page) {
                kfree(entry);
                return NULL;
        }

        entry->offset = 0;
        entry->len = 0;
        entry->end = 0;
        entry->users = 0;
        entry->con = con;

        return entry;
}

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

        con = nodeid2con(nodeid, allocation);
        if (!con)
                return NULL;

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

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

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

void dlm_lowcomms_commit_buffer(void *mh)
{
        struct writequeue_entry *e = (struct writequeue_entry *)mh;
        struct connection *con = e->con;
        int users;

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

        queue_work(send_workqueue, &con->swork);
        return;

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

/* Send a message */
static void send_to_sock(struct connection *con)
{
        int ret = 0;
        const int msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL;
        struct writequeue_entry *e;
        int len, offset;
        int count = 0;

        mutex_lock(&con->sock_mutex);
        if (con->sock == NULL)
                goto out_connect;

        spin_lock(&con->writequeue_lock);
        for (;;) {
                e = list_entry(con->writequeue.next, struct writequeue_entry,
                               list);
                if ((struct list_head *) e == &con->writequeue)
                        break;

                len = e->len;
                offset = e->offset;
                BUG_ON(len == 0 && e->users == 0);
                spin_unlock(&con->writequeue_lock);

                ret = 0;
                if (len) {
                        ret = kernel_sendpage(con->sock, e->page, offset, len,
                                              msg_flags);
                        if (ret == -EAGAIN || ret == 0) {
                                if (ret == -EAGAIN &&
                                    test_bit(SOCKWQ_ASYNC_NOSPACE, &con->sock->flags) &&
                                    !test_and_set_bit(CF_APP_LIMITED, &con->flags)) {
                                        /* Notify TCP that we're limited by the
                                         * application window size.
                                         */
                                        set_bit(SOCK_NOSPACE, &con->sock->flags);
                                        con->sock->sk->sk_write_pending++;
                                }
                                cond_resched();
                                goto out;
                        } else if (ret < 0)
                                goto send_error;
                }

                /* Don't starve people filling buffers */
                if (++count >= MAX_SEND_MSG_COUNT) {
                        cond_resched();
                        count = 0;
                }

                spin_lock(&con->writequeue_lock);
                writequeue_entry_complete(e, ret);
        }
        spin_unlock(&con->writequeue_lock);
out:
        mutex_unlock(&con->sock_mutex);
        return;

send_error:
        mutex_unlock(&con->sock_mutex);
        close_connection(con, true, false, true);
        /* Requeue the send work. When the work daemon runs again, it will try
           a new connection, then call this function again. */
        queue_work(send_workqueue, &con->swork);
        return;

out_connect:
        mutex_unlock(&con->sock_mutex);
        queue_work(send_workqueue, &con->swork);
        cond_resched();
}

static void clean_one_writequeue(struct connection *con)
{
        struct writequeue_entry *e, *safe;

        spin_lock(&con->writequeue_lock);
        list_for_each_entry_safe(e, safe, &con->writequeue, list) {
                list_del(&e->list);
                free_entry(e);
        }
        spin_unlock(&con->writequeue_lock);
}

/* Called from recovery when it knows that a node has
   left the cluster */
int dlm_lowcomms_close(int nodeid)
{
        struct connection *con;
        struct dlm_node_addr *na;

        log_print("closing connection to node %d", nodeid);
        con = nodeid2con(nodeid, 0);
        if (con) {
                set_bit(CF_CLOSE, &con->flags);
                close_connection(con, true, true, true);
                clean_one_writequeue(con);
        }

        spin_lock(&dlm_node_addrs_spin);
        na = find_node_addr(nodeid);
        if (na) {
                list_del(&na->list);
                while (na->addr_count--)
                        kfree(na->addr[na->addr_count]);
                kfree(na);
        }
        spin_unlock(&dlm_node_addrs_spin);

        return 0;
}

/* Receive workqueue function */
static void process_recv_sockets(struct work_struct *work)
{
        struct connection *con = container_of(work, struct connection, rwork);
        int err;

        clear_bit(CF_READ_PENDING, &con->flags);
        do {
                err = con->rx_action(con);
        } while (!err);
}

/* Send workqueue function */
static void process_send_sockets(struct work_struct *work)
{
        struct connection *con = container_of(work, struct connection, swork);

        clear_bit(CF_WRITE_PENDING, &con->flags);
        if (con->sock == NULL) /* not mutex protected so check it inside too */
                con->connect_action(con);
        if (!list_empty(&con->writequeue))
                send_to_sock(con);
}


/* Discard all entries on the write queues */
static void clean_writequeues(void)
{
        foreach_conn(clean_one_writequeue);
}

static void work_stop(void)
{
        if (recv_workqueue)
                destroy_workqueue(recv_workqueue);
        if (send_workqueue)
                destroy_workqueue(send_workqueue);
}

static int work_start(void)
{
        recv_workqueue = alloc_workqueue("dlm_recv",
                                         WQ_UNBOUND | WQ_MEM_RECLAIM, 1);
        if (!recv_workqueue) {
                log_print("can't start dlm_recv");
                return -ENOMEM;
        }

        send_workqueue = alloc_workqueue("dlm_send",
                                         WQ_UNBOUND | WQ_MEM_RECLAIM, 1);
        if (!send_workqueue) {
                log_print("can't start dlm_send");
                destroy_workqueue(recv_workqueue);
                return -ENOMEM;
        }

        return 0;
}

static void _stop_conn(struct connection *con, bool and_other)
{
        mutex_lock(&con->sock_mutex);
        set_bit(CF_CLOSE, &con->flags);
        set_bit(CF_READ_PENDING, &con->flags);
        set_bit(CF_WRITE_PENDING, &con->flags);
        if (con->sock && con->sock->sk) {
                write_lock_bh(&con->sock->sk->sk_callback_lock);
                con->sock->sk->sk_user_data = NULL;
                write_unlock_bh(&con->sock->sk->sk_callback_lock);
        }
        if (con->othercon && and_other)
                _stop_conn(con->othercon, false);
        mutex_unlock(&con->sock_mutex);
}

static void stop_conn(struct connection *con)
{
        _stop_conn(con, true);
}

static void free_conn(struct connection *con)
{
        close_connection(con, true, true, true);
        if (con->othercon)
                kmem_cache_free(con_cache, con->othercon);
        hlist_del(&con->list);
        kmem_cache_free(con_cache, con);
}

static void work_flush(void)
{
        int ok;
        int i;
        struct hlist_node *n;
        struct connection *con;

        if (recv_workqueue)
                flush_workqueue(recv_workqueue);
        if (send_workqueue)
                flush_workqueue(send_workqueue);
        do {
                ok = 1;
                foreach_conn(stop_conn);
                if (recv_workqueue)
                        flush_workqueue(recv_workqueue);
                if (send_workqueue)
                        flush_workqueue(send_workqueue);
                for (i = 0; i < CONN_HASH_SIZE && ok; i++) {
                        hlist_for_each_entry_safe(con, n,
                                                  &connection_hash[i], list) {
                                ok &= test_bit(CF_READ_PENDING, &con->flags);
                                ok &= test_bit(CF_WRITE_PENDING, &con->flags);
                                if (con->othercon) {
                                        ok &= test_bit(CF_READ_PENDING,
                                                       &con->othercon->flags);
                                        ok &= test_bit(CF_WRITE_PENDING,
                                                       &con->othercon->flags);
                                }
                        }
                }
        } while (!ok);
}

void dlm_lowcomms_stop(void)
{
        /* Set all the flags to prevent any
           socket activity.
        */
        mutex_lock(&connections_lock);
        dlm_allow_conn = 0;
        mutex_unlock(&connections_lock);
        work_flush();
        clean_writequeues();
        foreach_conn(free_conn);
        work_stop();

        kmem_cache_destroy(con_cache);
}

int dlm_lowcomms_start(void)
{
        int error = -EINVAL;
        struct connection *con;
        int i;

        for (i = 0; i < CONN_HASH_SIZE; i++)
                INIT_HLIST_HEAD(&connection_hash[i]);

        init_local();
        if (!dlm_local_count) {
                error = -ENOTCONN;
                log_print("no local IP address has been set");
                goto fail;
        }

        error = -ENOMEM;
        con_cache = kmem_cache_create("dlm_conn", sizeof(struct connection),
                                      __alignof__(struct connection), 0,
                                      NULL);
        if (!con_cache)
                goto fail;

        error = work_start();
        if (error)
                goto fail_destroy;

        dlm_allow_conn = 1;

        /* Start listening */
        if (dlm_config.ci_protocol == 0)
                error = tcp_listen_for_all();
        else
                error = sctp_listen_for_all();
        if (error)
                goto fail_unlisten;

        return 0;

fail_unlisten:
        dlm_allow_conn = 0;
        con = nodeid2con(0,0);
        if (con) {
                close_connection(con, false, true, true);
                kmem_cache_free(con_cache, con);
        }
fail_destroy:
        kmem_cache_destroy(con_cache);
fail:
        return error;
}

void dlm_lowcomms_exit(void)
{
        struct dlm_node_addr *na, *safe;

        spin_lock(&dlm_node_addrs_spin);
        list_for_each_entry_safe(na, safe, &dlm_node_addrs, list) {
                list_del(&na->list);
                while (na->addr_count--)
                        kfree(na->addr[na->addr_count]);
                kfree(na);
        }
        spin_unlock(&dlm_node_addrs_spin);
}