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lowcomms.c

/******************************************************************************
*******************************************************************************
**
**  Copyright (C) Sistina Software, Inc.  1997-2003  All rights reserved.
**  Copyright (C) 2004 Red Hat, Inc.  All rights reserved.
**
**  This copyrighted material is made available to anyone wishing to use,
**  modify, copy, or redistribute it subject to the terms and conditions
**  of the GNU General Public License v.2.
**
*******************************************************************************
******************************************************************************/

/*
 * lowcomms.c
 *
 * This is the "low-level" comms layer.
 *
 * It is responsible for sending/receiving messages
 * from other nodes in the cluster.
 *
 * Cluster nodes are referred to by their nodeids. nodeids are
 * simply 32 bit numbers to the locking module - if they need to
 * be expanded for the cluster infrastructure then that is it's
 * responsibility. It is this layer's
 * responsibility to resolve these into IP address or
 * whatever it needs for inter-node communication.
 *
 * The comms level is two kernel threads that deal mainly with
 * the receiving of messages from other nodes and passing them
 * up to the mid-level comms layer (which understands the
 * message format) for execution by the locking core, and
 * a send thread which does all the setting up of connections
 * to remote nodes and the sending of data. Threads are not allowed
 * to send their own data because it may cause them to wait in times
 * of high load. Also, this way, the sending thread can collect together
 * messages bound for one node and send them in one block.
 *
 * I don't see any problem with the recv thread executing the locking
 * code on behalf of remote processes as the locking code is
 * short, efficient and never waits.
 *
 */


#include <asm/ioctls.h>
#include <net/sock.h>
#include <net/tcp.h>
#include <linux/pagemap.h>
#include <cluster/cnxman.h>

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

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

#define CBUF_INIT(cb, size) do { (cb)->base = (cb)->len = 0; (cb)->mask = ((size)-1); } while(0)
#define CBUF_ADD(cb, n) do { (cb)->len += n; } while(0)
#define CBUF_EMPTY(cb) ((cb)->len == 0)
#define CBUF_MAY_ADD(cb, n) (((cb)->len + (n)) < ((cb)->mask + 1))
#define CBUF_EAT(cb, n) do { (cb)->len  -= (n); \
                             (cb)->base += (n); (cb)->base &= (cb)->mask; } while(0)
#define CBUF_DATA(cb) (((cb)->base + (cb)->len) & (cb)->mask)

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

struct connection {
      struct socket *sock;    /* NULL if not connected */
      uint32_t nodeid;  /* So we know who we are in the list */
      struct rw_semaphore sock_sem; /* Stop connect races */
      struct list_head read_list;   /* On this list when ready for reading */
      struct list_head write_list;  /* On this list when ready for writing */
      struct list_head state_list;  /* On this list when ready to connect */
      unsigned long flags;    /* bit 1,2 = We are on the read/write lists */
#define CF_READ_PENDING 1
#define CF_WRITE_PENDING 2
#define CF_CONNECT_PENDING 3
#define CF_IS_OTHERCON 4
      struct list_head writequeue;  /* List of outgoing writequeue_entries */
      struct list_head listenlist;    /* List of allocated listening sockets */
      spinlock_t writequeue_lock;
      int (*rx_action) (struct connection *);   /* What to do when active */
      struct page *rx_page;
      struct cbuf cb;
      int retries;
      atomic_t waiting_requests;
#define MAX_CONNECT_RETRIES 3
      struct connection *othercon;
};
#define sock2con(x) ((struct connection *)(x)->sk_user_data)

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

/* "Template" structure for IPv4 and IPv6 used to fill
 * in the missing bits when converting between cman (which knows
 * nothing about sockaddr structs) and real life where we actually
 * have to connect to these addresses. Also one of these structs
 * will hold the cached "us" address.
 *
 * It's an in6 sockaddr just so there's enough space for anything
 * we're likely to see here.
 */
static struct sockaddr_in6 local_addr;
static int our_nodeid = 0;

/* Manage daemons */
static struct task_struct *recv_task;
static struct task_struct *send_task;

static wait_queue_t lowcomms_send_waitq_head;
static wait_queue_head_t lowcomms_send_waitq;
static wait_queue_t lowcomms_recv_waitq_head;
static wait_queue_head_t lowcomms_recv_waitq;

/* An array of pointers to connections, indexed by NODEID */
static struct connection **connections;
static struct semaphore connections_lock;
static kmem_cache_t *con_cache;
static int conn_array_size;
static atomic_t accepting;

/* List of sockets that have reads pending */
static struct list_head read_sockets;
static spinlock_t read_sockets_lock;

/* List of sockets which have writes pending */
static struct list_head write_sockets;
static spinlock_t write_sockets_lock;

/* List of sockets which have connects pending */
static struct list_head state_sockets;
static spinlock_t state_sockets_lock;

/* List of allocated listen sockets */
static struct list_head listen_sockets;

static int lowcomms_ipaddr_from_nodeid(int nodeid, struct sockaddr *retaddr);
static int lowcomms_nodeid_from_ipaddr(struct sockaddr *addr, int addr_len);


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

      down(&connections_lock);
      if (nodeid >= conn_array_size) {
            int new_size = nodeid + dlm_config.conn_increment;
            struct connection **new_conns;

            new_conns = kmalloc(sizeof(struct connection *) *
                            new_size, allocation);
            if (!new_conns)
                  goto finish;

            memset(new_conns, 0, sizeof(struct connection *) * new_size);
            memcpy(new_conns, connections,  sizeof(struct connection *) * conn_array_size);
            conn_array_size = new_size;
            kfree(connections);
            connections = new_conns;

      }

      con = connections[nodeid];
      if (con == NULL && allocation) {
            con = kmem_cache_alloc(con_cache, allocation);
            if (!con)
                  goto finish;

            memset(con, 0, sizeof(*con));
            con->nodeid = nodeid;
            init_rwsem(&con->sock_sem);
            INIT_LIST_HEAD(&con->writequeue);
            spin_lock_init(&con->writequeue_lock);

            connections[nodeid] = con;
      }

 finish:
      up(&connections_lock);
      return con;
}

/* Data available on socket or listen socket received a connect */
static void lowcomms_data_ready(struct sock *sk, int count_unused)
{
      struct connection *con = sock2con(sk);

      atomic_inc(&con->waiting_requests);
      if (test_and_set_bit(CF_READ_PENDING, &con->flags))
            return;

      spin_lock_bh(&read_sockets_lock);
      list_add_tail(&con->read_list, &read_sockets);
      spin_unlock_bh(&read_sockets_lock);

      wake_up_interruptible(&lowcomms_recv_waitq);
}

static void lowcomms_write_space(struct sock *sk)
{
      struct connection *con = sock2con(sk);

      if (test_and_set_bit(CF_WRITE_PENDING, &con->flags))
            return;

      spin_lock_bh(&write_sockets_lock);
      list_add_tail(&con->write_list, &write_sockets);
      spin_unlock_bh(&write_sockets_lock);

      wake_up_interruptible(&lowcomms_send_waitq);
}

static inline void lowcomms_connect_sock(struct connection *con)
{
      if (test_and_set_bit(CF_CONNECT_PENDING, &con->flags))
            return;
      if (!atomic_read(&accepting))
            return;

      spin_lock_bh(&state_sockets_lock);
      list_add_tail(&con->state_list, &state_sockets);
      spin_unlock_bh(&state_sockets_lock);

      wake_up_interruptible(&lowcomms_send_waitq);
}

static void lowcomms_state_change(struct sock *sk)
{
/*    struct connection *con = sock2con(sk); */

      switch (sk->sk_state) {
      case TCP_ESTABLISHED:
            lowcomms_write_space(sk);
            break;

      case TCP_FIN_WAIT1:
      case TCP_FIN_WAIT2:
      case TCP_TIME_WAIT:
      case TCP_CLOSE:
      case TCP_CLOSE_WAIT:
      case TCP_LAST_ACK:
      case TCP_CLOSING:
            /* FIXME: I think this causes more trouble than it solves.
               lowcomms wil reconnect anyway when there is something to
               send. This just attempts reconnection if a node goes down!
            */
            /* lowcomms_connect_sock(con); */
            break;

      default:
            printk("dlm: lowcomms_state_change: state=%d\n", sk->sk_state);
            break;
      }
}

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

      /* Install a data_ready callback */
      con->sock->sk->sk_data_ready = lowcomms_data_ready;
      con->sock->sk->sk_write_space = lowcomms_write_space;
      con->sock->sk->sk_state_change = lowcomms_state_change;

      return 0;
}

/* Add the port number to an IP6 or 4 sockaddr and return the address
   length */
static void make_sockaddr(struct sockaddr_in6 *saddr, uint16_t port,
                    int *addr_len)
{
        saddr->sin6_family = local_addr.sin6_family;
        if (local_addr.sin6_family == AF_INET) {
            struct sockaddr_in *in4_addr = (struct sockaddr_in *)saddr;
            in4_addr->sin_port = cpu_to_be16(port);
            *addr_len = sizeof(struct sockaddr_in);
      }
      else {
            saddr->sin6_port = cpu_to_be16(port);
            *addr_len = sizeof(struct sockaddr_in6);
      }
}

/* Close a remote connection and tidy up */
static void close_connection(struct connection *con, int and_other)
{
      down_write(&con->sock_sem);

      if (con->sock) {
            sock_release(con->sock);
            con->sock = NULL;
      }
      if (con->othercon && and_other) {
            /* Argh! recursion in kernel code!
               Actually, this isn't a list so it
               will only re-enter once.
            */
            close_connection(con->othercon, FALSE);
      }
      if (con->rx_page) {
            __free_page(con->rx_page);
            con->rx_page = NULL;
      }
      con->retries = 0;
      up_write(&con->sock_sem);
}

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

      down_read(&con->sock_sem);

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

      /*
       * To avoid doing too many short reads, we will reschedule for
       * another time if there are less than 20 bytes left in the buffer.
       */
      if (!CBUF_MAY_ADD(&con->cb, 20))
            goto out_resched;

      msg.msg_control = NULL;
      msg.msg_controllen = 0;
      msg.msg_iovlen = 1;
      msg.msg_iov = iov;
      msg.msg_name = NULL;
      msg.msg_namelen = 0;
      msg.msg_flags = 0;

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

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

      fs = get_fs();
      set_fs(get_ds());
      r = ret = sock_recvmsg(con->sock, &msg, len,
                         MSG_DONTWAIT | MSG_NOSIGNAL);
      set_fs(fs);

      if (ret <= 0)
            goto out_close;
      if (ret == len)
            call_again_soon = 1;
      CBUF_ADD(&con->cb, ret);
      ret = midcomms_process_incoming_buffer(con->nodeid,
                                     page_address(con->rx_page),
                                     con->cb.base, con->cb.len,
                                     PAGE_CACHE_SIZE);
      if (ret == -EBADMSG) {
            printk(KERN_INFO "dlm: lowcomms: addr=%p, base=%u, len=%u, "
                   "iov_len=%u, iov_base[0]=%p, read=%d\n",
                   page_address(con->rx_page), con->cb.base, con->cb.len,
                   len, iov[0].iov_base, r);
      }
      if (ret < 0)
            goto out_close;
      CBUF_EAT(&con->cb, ret);

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

      out:
      if (call_again_soon)
            goto out_resched;
      up_read(&con->sock_sem);
      ret = 0;
      goto out_ret;

      out_resched:
      lowcomms_data_ready(con->sock->sk, 0);
      up_read(&con->sock_sem);
      ret = 0;
      schedule();
      goto out_ret;

      out_close:
      up_read(&con->sock_sem);
      if (ret != -EAGAIN && !test_bit(CF_IS_OTHERCON, &con->flags)) {
            close_connection(con, FALSE);
            /* Reconnect when there is something to send */
      }

      out_ret:
      return ret;
}

/* Listening socket is busy, accept a connection */
static int accept_from_sock(struct connection *con)
{
      int result;
      struct sockaddr_in6 peeraddr;
      struct socket *newsock;
      int len;
      int nodeid;
      struct connection *newcon;

      memset(&peeraddr, 0, sizeof(peeraddr));
      result = sock_create_kern(local_addr.sin6_family, SOCK_STREAM, IPPROTO_TCP, &newsock);
      if (result < 0)
            return -ENOMEM;

      down_read(&con->sock_sem);

      result = -ENOTCONN;
      if (con->sock == NULL)
            goto accept_err;

      newsock->type = con->sock->type;
      newsock->ops = con->sock->ops;

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

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

      /* Get the new node's NODEID */
      nodeid = lowcomms_nodeid_from_ipaddr((struct sockaddr *)&peeraddr, len);
      if (nodeid == 0) {
            printk("dlm: connect from non cluster node\n");
            sock_release(newsock);
            up_read(&con->sock_sem);
            return -1;
      }

      log_debug2("got connection from %d", nodeid);

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

            if (!othercon) {
                  othercon = kmem_cache_alloc(con_cache, GFP_KERNEL);
                  if (!othercon) {
                        printk("dlm: failed to allocate incoming socket\n");
                        up_write(&newcon->sock_sem);
                        result = -ENOMEM;
                        goto accept_err;
                  }
                  memset(othercon, 0, sizeof(*othercon));
                  othercon->nodeid = nodeid;
                  othercon->rx_action = receive_from_sock;
                  init_rwsem(&othercon->sock_sem);
                  set_bit(CF_IS_OTHERCON, &othercon->flags);
                  newcon->othercon = othercon;
            }
            othercon->sock = newsock;
            newsock->sk->sk_user_data = othercon;
            add_sock(newsock, othercon);
      }
      else {
            newsock->sk->sk_user_data = newcon;
            newcon->rx_action = receive_from_sock;
            add_sock(newsock, newcon);

      }

      up_write(&newcon->sock_sem);

      /*
       * Add it to the active queue in case we got data
       * beween processing the accept adding the socket
       * to the read_sockets list
       */
      lowcomms_data_ready(newsock->sk, 0);
      up_read(&con->sock_sem);

      return 0;

      accept_err:
      up_read(&con->sock_sem);
      sock_release(newsock);

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

/* Connect a new socket to its peer */
static int connect_to_sock(struct connection *con)
{
      int result = -EHOSTUNREACH;
      struct sockaddr_in6 saddr;
      int addr_len;
      struct socket *sock;

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

      down_write(&con->sock_sem);
      if (con->retries++ > MAX_CONNECT_RETRIES)
            goto out;

      /* Some odd races can cause double-connects, ignore them */
      if (con->sock) {
            result = 0;
            goto out;
      }

      /* Create a socket to communicate with */
      result = sock_create_kern(local_addr.sin6_family, SOCK_STREAM, IPPROTO_TCP, &sock);
      if (result < 0)
            goto out_err;

      memset(&saddr, 0, sizeof(saddr));
      if (lowcomms_ipaddr_from_nodeid(con->nodeid, (struct sockaddr *)&saddr) < 0)
              goto out_err;

      sock->sk->sk_user_data = con;
      con->rx_action = receive_from_sock;

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

      add_sock(sock, con);

      log_debug2("connecting to %d", con->nodeid);
      result =
          sock->ops->connect(sock, (struct sockaddr *) &saddr, addr_len,
                         O_NONBLOCK);
      if (result == -EINPROGRESS)
            result = 0;
      if (result != 0)
            goto out_err;

      out:
      up_write(&con->sock_sem);
      /*
       * Returning an error here means we've given up trying to connect to
       * a remote node, otherwise we return 0 and reschedule the connetion
       * attempt
       */
      return result;

      out_err:
      if (con->sock) {
            sock_release(con->sock);
            con->sock = NULL;
      }
      /*
       * Some errors are fatal and this list might need adjusting. For other
       * errors we try again until the max number of retries is reached.
       */
      if (result != -EHOSTUNREACH && result != -ENETUNREACH &&
          result != -ENETDOWN && result != EINVAL
          && result != -EPROTONOSUPPORT) {
            lowcomms_connect_sock(con);
            result = 0;
      }
      goto out;
}

static struct socket *create_listen_sock(struct connection *con, char *addr, int addr_len)
{
        struct socket *sock = NULL;
      mm_segment_t fs;
      int result = 0;
      int one = 1;
      struct sockaddr_in6 *saddr = (struct sockaddr_in6 *)addr;

      /* Create a socket to communicate with */
      result = sock_create_kern(local_addr.sin6_family, SOCK_STREAM, IPPROTO_TCP, &sock);
      if (result < 0) {
            printk("dlm: Can't create listening comms socket\n");
            goto create_out;
      }

      fs = get_fs();
      set_fs(get_ds());
      result = sock_setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (char *)&one, sizeof(one));
      set_fs(fs);
      if (result < 0) {
            printk("dlm: Failed to set SO_REUSEADDR on socket: result=%d\n",result);
      }
      sock->sk->sk_user_data = con;
      con->rx_action = accept_from_sock;
      con->sock = sock;

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

      fs = get_fs();
      set_fs(get_ds());

      result = sock_setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, (char *)&one, sizeof(one));
      set_fs(fs);
      if (result < 0) {
            printk("dlm: Set keepalive failed: %d\n", result);
      }

      result = sock->ops->listen(sock, 5);
      if (result < 0) {
            printk("dlm: Can't listen on port %d\n", dlm_config.tcp_port);
            sock_release(sock);
            sock = NULL;
            goto create_out;
      }

      create_out:
      return sock;
}


/* Listen on all interfaces */
static int listen_for_all(void)
{
      int result = 0;
      int nodeid;
      struct socket *sock = NULL;
      struct list_head *addr_list;
      struct connection *con = nodeid2con(0, GFP_KERNEL);
      struct cluster_node_addr *node_addr;
      char local_addr[sizeof(struct sockaddr_in6)];

      /* This will also fill in local_addr */
      nodeid = lowcomms_our_nodeid();

      addr_list = kcl_get_node_addresses(nodeid);
      if (!addr_list) {
              printk("dlm: cannot initialise comms layer\n");
            result = -ENOTCONN;
            goto create_out;
      }

      list_for_each_entry(node_addr, addr_list, list) {

            if (!con) {
                  con = kmem_cache_alloc(con_cache, GFP_KERNEL);
                  if (!con) {
                        printk("dlm: failed to allocate listen socket\n");
                        result = -ENOMEM;
                        goto create_out;
                  }
                  memset(con, 0, sizeof(*con));
                  init_rwsem(&con->sock_sem);
                  spin_lock_init(&con->writequeue_lock);
                  INIT_LIST_HEAD(&con->writequeue);
                  set_bit(CF_IS_OTHERCON, &con->flags);
            }

            memcpy(local_addr, node_addr->addr, node_addr->addr_len);
              sock = create_listen_sock(con, local_addr,
                                node_addr->addr_len);
            if (sock) {
                  add_sock(sock, con);

                  /* Keep a list of dynamically allocated listening sockets
                     so we can free them at shutdown */
                  if (test_bit(CF_IS_OTHERCON, &con->flags)) {
                        list_add_tail(&con->listenlist, &listen_sockets);
                  }
            }
            else {
                  result = -EADDRINUSE;
                  if (test_bit(CF_IS_OTHERCON, &con->flags))
                        kmem_cache_free(con_cache, con);
                  goto create_out;
            }

            con = NULL;
      }

      create_out:
      return result;
}



static struct writequeue_entry *new_writequeue_entry(struct connection *con,
                                         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;
      entry->con = con;

      return entry;
}

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

      if (!atomic_read(&accepting))
            return NULL;

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

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

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

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

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

      if (!atomic_read(&accepting))
            return;

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

      if (test_and_set_bit(CF_WRITE_PENDING, &con->flags) == 0) {
            spin_lock_bh(&write_sockets_lock);
            list_add_tail(&con->write_list, &write_sockets);
            spin_unlock_bh(&write_sockets_lock);

            wake_up_interruptible(&lowcomms_send_waitq);
      }
      return;

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

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

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

      down_read(&con->sock_sem);
      if (con->sock == NULL)
            goto out_connect;

      sendpage = con->sock->ops->sendpage;

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

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

            ret = 0;
            if (len) {
                  ret = sendpage(con->sock, e->page, offset, len,
                               msg_flags);
                  if (ret == -EAGAIN || ret == 0)
                        goto out;
                  if (ret <= 0)
                        goto send_error;
            }
            else {
                  /* Don't starve people filling buffers */
                  schedule();
            }

            spin_lock(&con->writequeue_lock);
            e->offset += ret;
            e->len -= ret;

            if (e->len == 0 && e->users == 0) {
                  list_del(&e->list);
                  free_entry(e);
                  continue;
            }
      }
      spin_unlock(&con->writequeue_lock);
      out:
      up_read(&con->sock_sem);
      return ret;

      send_error:
      up_read(&con->sock_sem);
      close_connection(con, FALSE);
      lowcomms_connect_sock(con);
      return ret;

      out_connect:
      up_read(&con->sock_sem);
      lowcomms_connect_sock(con);
      return 0;
}

static void clean_one_writequeue(struct connection *con)
{
      struct list_head *list;
      struct list_head *temp;

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

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

      if (!connections)
            goto out;

      log_debug2("closing connection to node %d", nodeid);
      con = nodeid2con(nodeid, 0);
      if (con) {
            clean_one_writequeue(con);
            close_connection(con, TRUE);
            atomic_set(&con->waiting_requests, 0);
      }
      return 0;

      out:
      return -1;
}

/* API send message call, may queue the request */
/* N.B. This is the old interface - use the new one for new calls */
int lowcomms_send_message(int nodeid, char *buf, int len, int allocation)
{
      struct writequeue_entry *e;
      char *b;

      e = lowcomms_get_buffer(nodeid, len, allocation, &b);
      if (e) {
            memcpy(b, buf, len);
            lowcomms_commit_buffer(e);
            return 0;
      }
      return -ENOBUFS;
}

/* Look for activity on active sockets */
static void process_sockets(void)
{
      struct list_head *list;
      struct list_head *temp;
      int count = 0;

      spin_lock_bh(&read_sockets_lock);
      list_for_each_safe(list, temp, &read_sockets) {

            struct connection *con =
                list_entry(list, struct connection, read_list);
            list_del(&con->read_list);
            clear_bit(CF_READ_PENDING, &con->flags);

            spin_unlock_bh(&read_sockets_lock);

            /* This can reach zero if we are processing requests
             * as they come in.
             */
            if (atomic_read(&con->waiting_requests) == 0) {
                  spin_lock_bh(&read_sockets_lock);
                  continue;
            }

            do {
                  con->rx_action(con);

                  /* Don't starve out everyone else */
                  if (++count >= MAX_RX_MSG_COUNT) {
                        schedule();
                        count = 0;
                  }

            } while (!atomic_dec_and_test(&con->waiting_requests) &&
                   !kthread_should_stop());

            spin_lock_bh(&read_sockets_lock);
      }
      spin_unlock_bh(&read_sockets_lock);
}

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

      spin_lock_bh(&write_sockets_lock);
      list_for_each_safe(list, temp, &write_sockets) {
            struct connection *con =
                list_entry(list, struct connection, write_list);
            clear_bit(CF_WRITE_PENDING, &con->flags);
            list_del(&con->write_list);

            spin_unlock_bh(&write_sockets_lock);

            ret = send_to_sock(con);
            if (ret < 0) {
            }
            spin_lock_bh(&write_sockets_lock);
      }
      spin_unlock_bh(&write_sockets_lock);
}

static void process_state_queue(void)
{
      struct list_head *list;
      struct list_head *temp;
      int ret;

      spin_lock_bh(&state_sockets_lock);
      list_for_each_safe(list, temp, &state_sockets) {
            struct connection *con =
                list_entry(list, struct connection, state_list);
            list_del(&con->state_list);
            clear_bit(CF_CONNECT_PENDING, &con->flags);
            spin_unlock_bh(&state_sockets_lock);

            ret = connect_to_sock(con);
            if (ret < 0) {
            }
            spin_lock_bh(&state_sockets_lock);
      }
      spin_unlock_bh(&state_sockets_lock);
}


/* Discard all entries on the write queues */
static void clean_writequeues(void)
{
      int nodeid;

      for (nodeid = 1; nodeid < conn_array_size; nodeid++) {
            struct connection *con = nodeid2con(nodeid, 0);

            if (con)
                  clean_one_writequeue(con);
      }
}

static int read_list_empty(void)
{
      int status;

      spin_lock_bh(&read_sockets_lock);
      status = list_empty(&read_sockets);
      spin_unlock_bh(&read_sockets_lock);

      return status;
}

/* DLM Transport comms receive daemon */
static int dlm_recvd(void *data)
{
      init_waitqueue_head(&lowcomms_recv_waitq);
      init_waitqueue_entry(&lowcomms_recv_waitq_head, current);
      add_wait_queue(&lowcomms_recv_waitq, &lowcomms_recv_waitq_head);

      while (!kthread_should_stop()) {
            set_current_state(TASK_INTERRUPTIBLE);
            if (read_list_empty())
                  schedule();
            set_current_state(TASK_RUNNING);

            process_sockets();
      }

      return 0;
}

static int write_and_state_lists_empty(void)
{
      int status;

      spin_lock_bh(&write_sockets_lock);
      status = list_empty(&write_sockets);
      spin_unlock_bh(&write_sockets_lock);

      spin_lock_bh(&state_sockets_lock);
      if (list_empty(&state_sockets) == 0)
            status = 0;
      spin_unlock_bh(&state_sockets_lock);

      return status;
}

/* DLM Transport send daemon */
static int dlm_sendd(void *data)
{
      init_waitqueue_head(&lowcomms_send_waitq);
      init_waitqueue_entry(&lowcomms_send_waitq_head, current);
      add_wait_queue(&lowcomms_send_waitq, &lowcomms_send_waitq_head);

      while (!kthread_should_stop()) {
            set_current_state(TASK_INTERRUPTIBLE);
            if (write_and_state_lists_empty())
                  schedule();
            set_current_state(TASK_RUNNING);

            process_state_queue();
            process_output_queue();
      }

      return 0;
}

static void daemons_stop(void)
{
      kthread_stop(recv_task);
      kthread_stop(send_task);
}

static int daemons_start(void)
{
      struct task_struct *p;
      int error;

      p = kthread_run(dlm_recvd, NULL, "dlm_recvd");
      error = IS_ERR(p);
            if (error) {
            log_print("can't start dlm_recvd %d", error);
            return error;
      }
      recv_task = p;

      p = kthread_run(dlm_sendd, NULL, "dlm_sendd");
      error = IS_ERR(p);
            if (error) {
            log_print("can't start dlm_sendd %d", error);
            kthread_stop(recv_task);
            return error;
      }
      send_task = p;

      return 0;
}

/*
 * Return the largest buffer size we can cope with.
 */
int lowcomms_max_buffer_size(void)
{
      return PAGE_CACHE_SIZE;
}

void lowcomms_stop(void)
{
      int i;
      struct connection *temp;
      struct connection *lcon;

      atomic_set(&accepting, 0);

      /* Set all the activity flags to prevent any
         socket activity.
      */
      for (i = 0; i < conn_array_size; i++) {
            if (connections[i])
                  connections[i]->flags |= 0x7;
      }
      daemons_stop();
      clean_writequeues();

      for (i = 0; i < conn_array_size; i++) {
            if (connections[i]) {
                  close_connection(connections[i], TRUE);
                  if (connections[i]->othercon)
                        kmem_cache_free(con_cache, connections[i]->othercon);
                  kmem_cache_free(con_cache, connections[i]);
            }
      }

      kfree(connections);
      connections = NULL;

      /* Free up any dynamically allocated listening sockets */
      list_for_each_entry_safe(lcon, temp, &listen_sockets, listenlist) {
            sock_release(lcon->sock);
            kmem_cache_free(con_cache, lcon);
      }

      kmem_cache_destroy(con_cache);
      kcl_releaseref_cluster();
      our_nodeid = 0;
}

/* This is quite likely to sleep... */
int lowcomms_start(void)
{
      int error = 0;
      struct connection *temp;
      struct connection *lcon;

      INIT_LIST_HEAD(&read_sockets);
      INIT_LIST_HEAD(&write_sockets);
      INIT_LIST_HEAD(&state_sockets);
      INIT_LIST_HEAD(&listen_sockets);

      spin_lock_init(&read_sockets_lock);
      spin_lock_init(&write_sockets_lock);
      spin_lock_init(&state_sockets_lock);
      init_MUTEX(&connections_lock);

      error = -ENOTCONN;
      if (kcl_addref_cluster())
            goto out;

      /*
       * Temporarily initialise the waitq head so that lowcomms_send_message
       * doesn't crash if it gets called before the thread is fully
       * initialised
       */
      init_waitqueue_head(&lowcomms_send_waitq);

      error = -ENOMEM;
      connections = kmalloc(sizeof(struct connection *) *
                        dlm_config.conn_increment, GFP_KERNEL);
      if (!connections)
            goto out;

      memset(connections, 0,
             sizeof(struct connection *) * dlm_config.conn_increment);

      conn_array_size = dlm_config.conn_increment;

      con_cache = kmem_cache_create("dlm_conn", sizeof(struct connection),
                              __alignof__(struct connection), 0, NULL, NULL);
      if (!con_cache)
            goto fail_free_conn;


      /* Start listening */
      error = listen_for_all();
      if (error)
            goto fail_unlisten;

      error = daemons_start();
      if (error)
            goto fail_unlisten;

      atomic_set(&accepting, 1);

      return 0;

      fail_unlisten:
      close_connection(connections[0], 0);
      kmem_cache_free(con_cache, connections[0]);
      list_for_each_entry_safe(lcon, temp, &listen_sockets, listenlist) {
            sock_release(lcon->sock);
            kmem_cache_free(con_cache, lcon);
      }

      kmem_cache_destroy(con_cache);

      fail_free_conn:
      kcl_releaseref_cluster();
      kfree(connections);

      out:
      return error;
}

/* Don't accept any more outgoing work */
void lowcomms_stop_accept()
{
        atomic_set(&accepting, 0);
}

/* Cluster Manager interface functions for looking up
   nodeids and IP addresses by each other
*/

/* Return the IP address of a node given its NODEID */
static int lowcomms_ipaddr_from_nodeid(int nodeid, struct sockaddr *retaddr)
{
      struct list_head *addrs;
      struct cluster_node_addr *node_addr;
      struct cluster_node_addr *current_addr = NULL;
      struct sockaddr_in6 *saddr;
      int interface;
      int i;

      addrs = kcl_get_node_addresses(nodeid);
      if (!addrs)
            return -1;

      interface = kcl_get_current_interface();

      /* Look for address number <interface> */
      i=0; /* i/f numbers start at 1 */
      list_for_each_entry(node_addr, addrs, list) {
              if (interface == ++i) {
                    current_addr = node_addr;
                  break;
            }
      }

      /* If that failed then just use the first one */
      if (!current_addr)
              current_addr = (struct cluster_node_addr *)addrs->next;

      saddr = (struct sockaddr_in6 *)current_addr->addr;

      /* Extract the IP address */
      if (local_addr.sin6_family == AF_INET) {
              struct sockaddr_in *in4  = (struct sockaddr_in *)saddr;
            struct sockaddr_in *ret4 = (struct sockaddr_in *)retaddr;
            ret4->sin_addr.s_addr = in4->sin_addr.s_addr;
      }
      else {
              struct sockaddr_in6 *ret6 = (struct sockaddr_in6 *)retaddr;
            memcpy(&ret6->sin6_addr, &saddr->sin6_addr, sizeof(saddr->sin6_addr));
      }

      return 0;
}

/* Return the NODEID for a node given its sockaddr */
static int lowcomms_nodeid_from_ipaddr(struct sockaddr *addr, int addr_len)
{
      struct kcl_cluster_node node;
      struct sockaddr_in6 ipv6_addr;
      struct sockaddr_in  ipv4_addr;

      if (local_addr.sin6_family == AF_INET) {
              struct sockaddr_in *in4 = (struct sockaddr_in *)addr;
            memcpy(&ipv4_addr, &local_addr, addr_len);
            memcpy(&ipv4_addr.sin_addr, &in4->sin_addr, sizeof(ipv4_addr.sin_addr));

            addr = (struct sockaddr *)&ipv4_addr;
      }
      else {
              struct sockaddr_in6 *in6 = (struct sockaddr_in6 *)addr;
            memcpy(&ipv6_addr, &local_addr, addr_len);
            memcpy(&ipv6_addr.sin6_addr, &in6->sin6_addr, sizeof(ipv6_addr.sin6_addr));

            addr = (struct sockaddr *)&ipv6_addr;
      }

      if (kcl_get_node_by_addr((char *)addr, addr_len, &node) == 0)
            return node.node_id;
      else
            return 0;
}

int lowcomms_our_nodeid(void)
{
      struct kcl_cluster_node node;
      struct list_head *addrs;
      struct cluster_node_addr *first_addr;

      if (our_nodeid)
            return our_nodeid;

      if (kcl_get_node_by_nodeid(0, &node) == -1)
            return 0;

      our_nodeid = node.node_id;

      /* Fill in the "template" structure */
      addrs = kcl_get_node_addresses(our_nodeid);
      if (!addrs)
            return 0;

      first_addr = (struct cluster_node_addr *) addrs->next;
      memcpy(&local_addr, &first_addr->addr, first_addr->addr_len);

      return node.node_id;
}
/*
 * Overrides for Emacs so that we follow Linus's tabbing style.
 * Emacs will notice this stuff at the end of the file and automatically
 * adjust the settings for this buffer only.  This must remain at the end
 * of the file.
 * ---------------------------------------------------------------------------
 * Local variables:
 * c-file-style: "linux"
 * End:
 */

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