ClabureDB: Classified Bug-Reports Database

  /*
   * IPVS         An implementation of the IP virtual server support for the
   *              LINUX operating system.  IPVS is now implemented as a module
   *              over the NetFilter framework. IPVS can be used to build a
   *              high-performance and highly available server based on a
   *              cluster of servers.
   *
   * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
   *
  * ip_vs_sync:  sync connection info from master load balancer to backups
  *              through multicast
  *
  * Changes:
  *        Alexandre Cassen        :        Added master & backup support at a time.
  *        Alexandre Cassen        :        Added SyncID support for incoming sync
  *                                        messages filtering.
  *        Justin Ossevoort        :        Fix endian problem on sync message size.
  */
 
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/inetdevice.h>
 #include <linux/net.h>
 #include <linux/completion.h>
 #include <linux/delay.h>
 #include <linux/skbuff.h>
 #include <linux/in.h>
 #include <linux/igmp.h>                 /* for ip_mc_join_group */
 #include <linux/udp.h>
 #include <linux/err.h>
 #include <linux/kthread.h>
 #include <linux/wait.h>
 #include <linux/kernel.h>
 
 #include <net/ip.h>
 #include <net/sock.h>
 
 #include <net/ip_vs.h>
 
 #define IP_VS_SYNC_GROUP 0xe0000051    /* multicast addr - 224.0.0.81 */
 #define IP_VS_SYNC_PORT  8848          /* multicast port */
 
 
 /*
  *        IPVS sync connection entry
  */
 struct ip_vs_sync_conn {
         __u8                        reserved;
 
         /* Protocol, addresses and port numbers */
         __u8                        protocol;       /* Which protocol (TCP/UDP) */
         __be16                        cport;
         __be16                  vport;
         __be16                  dport;
         __be32                  caddr;          /* client address */
         __be32                  vaddr;          /* virtual address */
         __be32                  daddr;          /* destination address */
 
         /* Flags and state transition */
         __be16                  flags;          /* status flags */
         __be16                  state;          /* state info */
 
         /* The sequence options start here */
 };
 
 struct ip_vs_sync_conn_options {
         struct ip_vs_seq        in_seq;         /* incoming seq. struct */
         struct ip_vs_seq        out_seq;        /* outgoing seq. struct */
 };
 
 struct ip_vs_sync_thread_data {
         struct socket *sock;
         char *buf;
 };
 
 #define SIMPLE_CONN_SIZE  (sizeof(struct ip_vs_sync_conn))
 #define FULL_CONN_SIZE  \
 (sizeof(struct ip_vs_sync_conn) + sizeof(struct ip_vs_sync_conn_options))
 
 
 /*
   The master mulitcasts messages to the backup load balancers in the
   following format.
 
        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Count Conns  |    SyncID     |            Size               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                    IPVS Sync Connection (1)                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            .                                  |
       |                            .                                  |
       |                            .                                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                    IPVS Sync Connection (n)                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*/

#define SYNC_MESG_HEADER_LEN        4
#define MAX_CONNS_PER_SYNCBUFF        255 /* nr_conns in ip_vs_sync_mesg is 8 bit */

struct ip_vs_sync_mesg {
        __u8                    nr_conns;
        __u8                    syncid;
        __u16                   size;

        /* ip_vs_sync_conn entries start here */
};

/* the maximum length of sync (sending/receiving) message */
static int sync_send_mesg_maxlen;
static int sync_recv_mesg_maxlen;

struct ip_vs_sync_buff {
        struct list_head        list;
        unsigned long           firstuse;

        /* pointers for the message data */
        struct ip_vs_sync_mesg  *mesg;
        unsigned char           *head;
        unsigned char           *end;
};


/* the sync_buff list head and the lock */
static LIST_HEAD(ip_vs_sync_queue);
static DEFINE_SPINLOCK(ip_vs_sync_lock);

/* current sync_buff for accepting new conn entries */
static struct ip_vs_sync_buff   *curr_sb = NULL;
static DEFINE_SPINLOCK(curr_sb_lock);

/* ipvs sync daemon state */
volatile int ip_vs_sync_state = IP_VS_STATE_NONE;
volatile int ip_vs_master_syncid = 0;
volatile int ip_vs_backup_syncid = 0;

/* multicast interface name */
char ip_vs_master_mcast_ifn[IP_VS_IFNAME_MAXLEN];
char ip_vs_backup_mcast_ifn[IP_VS_IFNAME_MAXLEN];

/* sync daemon tasks */
static struct task_struct *sync_master_thread;
static struct task_struct *sync_backup_thread;

/* multicast addr */
static struct sockaddr_in mcast_addr = {
        .sin_family                = AF_INET,
        .sin_port                = __constant_htons(IP_VS_SYNC_PORT),
        .sin_addr.s_addr        = __constant_htonl(IP_VS_SYNC_GROUP),
};


static inline struct ip_vs_sync_buff *sb_dequeue(void)
{
        struct ip_vs_sync_buff *sb;

        spin_lock_bh(&ip_vs_sync_lock);
        if (list_empty(&ip_vs_sync_queue)) {
                sb = NULL;
        } else {
                sb = list_entry(ip_vs_sync_queue.next,
                                struct ip_vs_sync_buff,
                                list);
                list_del(&sb->list);
        }
        spin_unlock_bh(&ip_vs_sync_lock);

        return sb;
}

static inline struct ip_vs_sync_buff * ip_vs_sync_buff_create(void)
{
        struct ip_vs_sync_buff *sb;

        if (!(sb=kmalloc(sizeof(struct ip_vs_sync_buff), GFP_ATOMIC)))
                return NULL;

        if (!(sb->mesg=kmalloc(sync_send_mesg_maxlen, GFP_ATOMIC))) {
                kfree(sb);
                return NULL;
        }
        sb->mesg->nr_conns = 0;
        sb->mesg->syncid = ip_vs_master_syncid;
        sb->mesg->size = 4;
        sb->head = (unsigned char *)sb->mesg + 4;
        sb->end = (unsigned char *)sb->mesg + sync_send_mesg_maxlen;
        sb->firstuse = jiffies;
        return sb;
}

static inline void ip_vs_sync_buff_release(struct ip_vs_sync_buff *sb)
{
        kfree(sb->mesg);
        kfree(sb);
}

static inline void sb_queue_tail(struct ip_vs_sync_buff *sb)
{
        spin_lock(&ip_vs_sync_lock);
        if (ip_vs_sync_state & IP_VS_STATE_MASTER)
                list_add_tail(&sb->list, &ip_vs_sync_queue);
        else
                ip_vs_sync_buff_release(sb);
        spin_unlock(&ip_vs_sync_lock);
}

/*
 *        Get the current sync buffer if it has been created for more
 *        than the specified time or the specified time is zero.
 */
static inline struct ip_vs_sync_buff *
get_curr_sync_buff(unsigned long time)
{
        struct ip_vs_sync_buff *sb;

        spin_lock_bh(&curr_sb_lock);
        if (curr_sb && (time == 0 ||
                        time_before(jiffies - curr_sb->firstuse, time))) {
                sb = curr_sb;
                curr_sb = NULL;
        } else
                sb = NULL;
        spin_unlock_bh(&curr_sb_lock);
        return sb;
}


/*
 *      Add an ip_vs_conn information into the current sync_buff.
 *      Called by ip_vs_in.
 */
void ip_vs_sync_conn(struct ip_vs_conn *cp)
{
        struct ip_vs_sync_mesg *m;
        struct ip_vs_sync_conn *s;
        int len;

        spin_lock(&curr_sb_lock);
        if (!curr_sb) {
                if (!(curr_sb=ip_vs_sync_buff_create())) {
                        spin_unlock(&curr_sb_lock);
                        IP_VS_ERR("ip_vs_sync_buff_create failed.\n");
                        return;
                }
        }

        len = (cp->flags & IP_VS_CONN_F_SEQ_MASK) ? FULL_CONN_SIZE :
                SIMPLE_CONN_SIZE;
        m = curr_sb->mesg;
        s = (struct ip_vs_sync_conn *)curr_sb->head;

        /* copy members */
        s->protocol = cp->protocol;
        s->cport = cp->cport;
        s->vport = cp->vport;
        s->dport = cp->dport;
        s->caddr = cp->caddr.ip;
        s->vaddr = cp->vaddr.ip;
        s->daddr = cp->daddr.ip;
        s->flags = htons(cp->flags & ~IP_VS_CONN_F_HASHED);
        s->state = htons(cp->state);
        if (cp->flags & IP_VS_CONN_F_SEQ_MASK) {
                struct ip_vs_sync_conn_options *opt =
                        (struct ip_vs_sync_conn_options *)&s[1];
                memcpy(opt, &cp->in_seq, sizeof(*opt));
        }

        m->nr_conns++;
        m->size += len;
        curr_sb->head += len;

        /* check if there is a space for next one */
        if (curr_sb->head+FULL_CONN_SIZE > curr_sb->end) {
                sb_queue_tail(curr_sb);
                curr_sb = NULL;
        }
        spin_unlock(&curr_sb_lock);

        /* synchronize its controller if it has */
        if (cp->control)
                ip_vs_sync_conn(cp->control);
}


/*
 *      Process received multicast message and create the corresponding
 *      ip_vs_conn entries.
 */
static void ip_vs_process_message(const char *buffer, const size_t buflen)
{
        struct ip_vs_sync_mesg *m = (struct ip_vs_sync_mesg *)buffer;
        struct ip_vs_sync_conn *s;
        struct ip_vs_sync_conn_options *opt;
        struct ip_vs_conn *cp;
        struct ip_vs_protocol *pp;
        struct ip_vs_dest *dest;
        char *p;
        int i;

        if (buflen < sizeof(struct ip_vs_sync_mesg)) {
                IP_VS_ERR_RL("sync message header too short\n");
                return;
        }

        /* Convert size back to host byte order */
        m->size = ntohs(m->size);

        if (buflen != m->size) {
                IP_VS_ERR_RL("bogus sync message size\n");
                return;
        }

        /* SyncID sanity check */
        if (ip_vs_backup_syncid != 0 && m->syncid != ip_vs_backup_syncid) {
                IP_VS_DBG(7, "Ignoring incoming msg with syncid = %d\n",
                          m->syncid);
                return;
        }

        p = (char *)buffer + sizeof(struct ip_vs_sync_mesg);
        for (i=0; i<m->nr_conns; i++) {
                unsigned flags, state;

                if (p + SIMPLE_CONN_SIZE > buffer+buflen) {
                        IP_VS_ERR_RL("bogus conn in sync message\n");
                        return;
                }
                s = (struct ip_vs_sync_conn *) p;
                flags = ntohs(s->flags) | IP_VS_CONN_F_SYNC;
                flags &= ~IP_VS_CONN_F_HASHED;
                if (flags & IP_VS_CONN_F_SEQ_MASK) {
                        opt = (struct ip_vs_sync_conn_options *)&s[1];
                        p += FULL_CONN_SIZE;
                        if (p > buffer+buflen) {
                                IP_VS_ERR_RL("bogus conn options in sync message\n");
                                return;
                        }
                } else {
                        opt = NULL;
                        p += SIMPLE_CONN_SIZE;
                }

                state = ntohs(s->state);
                if (!(flags & IP_VS_CONN_F_TEMPLATE)) {
                        pp = ip_vs_proto_get(s->protocol);
                        if (!pp) {
                                IP_VS_ERR_RL("Unsupported protocol %u in sync msg\n",
                                        s->protocol);
                                continue;
                        }
                        if (state >= pp->num_states) {
                                IP_VS_DBG(2, "Invalid %s state %u in sync msg\n",
                                        pp->name, state);
                                continue;
                        }
                } else {
                        /* protocol in templates is not used for state/timeout */
                        pp = NULL;
                        if (state > 0) {
                                IP_VS_DBG(2, "Invalid template state %u in sync msg\n",
                                        state);
                                state = 0;
                        }
                }

                if (!(flags & IP_VS_CONN_F_TEMPLATE))
                        cp = ip_vs_conn_in_get(AF_INET, s->protocol,
                                               (union nf_inet_addr *)&s->caddr,
                                               s->cport,
                                               (union nf_inet_addr *)&s->vaddr,
                                               s->vport);
                else
                        cp = ip_vs_ct_in_get(AF_INET, s->protocol,
                                             (union nf_inet_addr *)&s->caddr,
                                             s->cport,
                                             (union nf_inet_addr *)&s->vaddr,
                                             s->vport);
                if (!cp) {
                        /*
                         * Find the appropriate destination for the connection.
                         * If it is not found the connection will remain unbound
                         * but still handled.
                         */
                        dest = ip_vs_find_dest(AF_INET,
                                               (union nf_inet_addr *)&s->daddr,
                                               s->dport,
                                               (union nf_inet_addr *)&s->vaddr,
                                               s->vport,
                                               s->protocol);
                        /*  Set the approprite ativity flag */
                        if (s->protocol == IPPROTO_TCP) {
                                if (state != IP_VS_TCP_S_ESTABLISHED)
                                        flags |= IP_VS_CONN_F_INACTIVE;
                                else
                                        flags &= ~IP_VS_CONN_F_INACTIVE;
                        }
                        cp = ip_vs_conn_new(AF_INET, s->protocol,
                                            (union nf_inet_addr *)&s->caddr,
                                            s->cport,
                                            (union nf_inet_addr *)&s->vaddr,
                                            s->vport,
                                            (union nf_inet_addr *)&s->daddr,
                                            s->dport,
                                            flags, dest);
                        if (dest)
                                atomic_dec(&dest->refcnt);
                        if (!cp) {
                                IP_VS_ERR("ip_vs_conn_new failed\n");
                                return;
                        }
                } else if (!cp->dest) {
                        dest = ip_vs_try_bind_dest(cp);
                        if (dest)
                                atomic_dec(&dest->refcnt);
                } else if ((cp->dest) && (cp->protocol == IPPROTO_TCP) &&
                           (cp->state != state)) {
                        /* update active/inactive flag for the connection */
                        dest = cp->dest;
                        if (!(cp->flags & IP_VS_CONN_F_INACTIVE) &&
                                (state != IP_VS_TCP_S_ESTABLISHED)) {
                                atomic_dec(&dest->activeconns);
                                atomic_inc(&dest->inactconns);
                                cp->flags |= IP_VS_CONN_F_INACTIVE;
                        } else if ((cp->flags & IP_VS_CONN_F_INACTIVE) &&
                                (state == IP_VS_TCP_S_ESTABLISHED)) {
                                atomic_inc(&dest->activeconns);
                                atomic_dec(&dest->inactconns);
                                cp->flags &= ~IP_VS_CONN_F_INACTIVE;
                        }
                }

                if (opt)
                        memcpy(&cp->in_seq, opt, sizeof(*opt));
                atomic_set(&cp->in_pkts, sysctl_ip_vs_sync_threshold[0]);
                cp->state = state;
                cp->old_state = cp->state;
                /*
                 * We can not recover the right timeout for templates
                 * in all cases, we can not find the right fwmark
                 * virtual service. If needed, we can do it for
                 * non-fwmark persistent services.
                 */
                if (!(flags & IP_VS_CONN_F_TEMPLATE) && pp->timeout_table)
                        cp->timeout = pp->timeout_table[state];
                else
                        cp->timeout = (3*60*HZ);
                ip_vs_conn_put(cp);
        }
}


/*
 *      Setup loopback of outgoing multicasts on a sending socket
 */
static void set_mcast_loop(struct sock *sk, u_char loop)
{
        struct inet_sock *inet = inet_sk(sk);

        /* setsockopt(sock, SOL_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop)); */
        lock_sock(sk);
        inet->mc_loop = loop ? 1 : 0;
        release_sock(sk);
}

/*
 *      Specify TTL for outgoing multicasts on a sending socket
 */
static void set_mcast_ttl(struct sock *sk, u_char ttl)
{
        struct inet_sock *inet = inet_sk(sk);

        /* setsockopt(sock, SOL_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl)); */
        lock_sock(sk);
        inet->mc_ttl = ttl;
        release_sock(sk);
}

/*
 *      Specifiy default interface for outgoing multicasts
 */
static int set_mcast_if(struct sock *sk, char *ifname)
{
        struct net_device *dev;
        struct inet_sock *inet = inet_sk(sk);

        if ((dev = __dev_get_by_name(&init_net, ifname)) == NULL)
                return -ENODEV;

        if (sk->sk_bound_dev_if && dev->ifindex != sk->sk_bound_dev_if)
                return -EINVAL;

        lock_sock(sk);
        inet->mc_index = dev->ifindex;
        /*  inet->mc_addr  = 0; */
        release_sock(sk);

        return 0;
}


/*
 *        Set the maximum length of sync message according to the
 *        specified interface's MTU.
 */
static int set_sync_mesg_maxlen(int sync_state)
{
        struct net_device *dev;
        int num;

        if (sync_state == IP_VS_STATE_MASTER) {
                if ((dev = __dev_get_by_name(&init_net, ip_vs_master_mcast_ifn)) == NULL)
                        return -ENODEV;

                num = (dev->mtu - sizeof(struct iphdr) -
                       sizeof(struct udphdr) -
                       SYNC_MESG_HEADER_LEN - 20) / SIMPLE_CONN_SIZE;
                sync_send_mesg_maxlen = SYNC_MESG_HEADER_LEN +
                        SIMPLE_CONN_SIZE * min(num, MAX_CONNS_PER_SYNCBUFF);
                IP_VS_DBG(7, "setting the maximum length of sync sending "
                          "message %d.\n", sync_send_mesg_maxlen);
        } else if (sync_state == IP_VS_STATE_BACKUP) {
                if ((dev = __dev_get_by_name(&init_net, ip_vs_backup_mcast_ifn)) == NULL)
                        return -ENODEV;

                sync_recv_mesg_maxlen = dev->mtu -
                        sizeof(struct iphdr) - sizeof(struct udphdr);
                IP_VS_DBG(7, "setting the maximum length of sync receiving "
                          "message %d.\n", sync_recv_mesg_maxlen);
        }

        return 0;
}


/*
 *      Join a multicast group.
 *      the group is specified by a class D multicast address 224.0.0.0/8
 *      in the in_addr structure passed in as a parameter.
 */
static int
join_mcast_group(struct sock *sk, struct in_addr *addr, char *ifname)
{
        struct ip_mreqn mreq;
        struct net_device *dev;
        int ret;

        memset(&mreq, 0, sizeof(mreq));
        memcpy(&mreq.imr_multiaddr, addr, sizeof(struct in_addr));

        if ((dev = __dev_get_by_name(&init_net, ifname)) == NULL)
                return -ENODEV;
        if (sk->sk_bound_dev_if && dev->ifindex != sk->sk_bound_dev_if)
                return -EINVAL;

        mreq.imr_ifindex = dev->ifindex;

        lock_sock(sk);
        ret = ip_mc_join_group(sk, &mreq);
        release_sock(sk);

        return ret;
}


static int bind_mcastif_addr(struct socket *sock, char *ifname)
{
        struct net_device *dev;
        __be32 addr;
        struct sockaddr_in sin;

        if ((dev = __dev_get_by_name(&init_net, ifname)) == NULL)
                return -ENODEV;

        addr = inet_select_addr(dev, 0, RT_SCOPE_UNIVERSE);
        if (!addr)
                IP_VS_ERR("You probably need to specify IP address on "
                          "multicast interface.\n");

        IP_VS_DBG(7, "binding socket with (%s) %u.%u.%u.%u\n",
                  ifname, NIPQUAD(addr));

        /* Now bind the socket with the address of multicast interface */
        sin.sin_family             = AF_INET;
        sin.sin_addr.s_addr  = addr;
        sin.sin_port         = 0;

        return sock->ops->bind(sock, (struct sockaddr*)&sin, sizeof(sin));
}

/*
 *      Set up sending multicast socket over UDP
 */
static struct socket * make_send_sock(void)
{
        struct socket *sock;
        int result;

        /* First create a socket */
        result = sock_create_kern(PF_INET, SOCK_DGRAM, IPPROTO_UDP, &sock);
        if (result < 0) {
                IP_VS_ERR("Error during creation of socket; terminating\n");
                return ERR_PTR(result);
        }

        result = set_mcast_if(sock->sk, ip_vs_master_mcast_ifn);
        if (result < 0) {
                IP_VS_ERR("Error setting outbound mcast interface\n");
                goto error;
        }

        set_mcast_loop(sock->sk, 0);
        set_mcast_ttl(sock->sk, 1);

        result = bind_mcastif_addr(sock, ip_vs_master_mcast_ifn);
        if (result < 0) {
                IP_VS_ERR("Error binding address of the mcast interface\n");
                goto error;
        }

        result = sock->ops->connect(sock, (struct sockaddr *) &mcast_addr,
                        sizeof(struct sockaddr), 0);
        if (result < 0) {
                IP_VS_ERR("Error connecting to the multicast addr\n");
                goto error;
        }

        return sock;

  error:
        sock_release(sock);
        return ERR_PTR(result);
}


/*
 *      Set up receiving multicast socket over UDP
 */
static struct socket * make_receive_sock(void)
{
        struct socket *sock;
        int result;

        /* First create a socket */
        result = sock_create_kern(PF_INET, SOCK_DGRAM, IPPROTO_UDP, &sock);
        if (result < 0) {
                IP_VS_ERR("Error during creation of socket; terminating\n");
                return ERR_PTR(result);
        }

        /* it is equivalent to the REUSEADDR option in user-space */
        sock->sk->sk_reuse = 1;

        result = sock->ops->bind(sock, (struct sockaddr *) &mcast_addr,
                        sizeof(struct sockaddr));
        if (result < 0) {
                IP_VS_ERR("Error binding to the multicast addr\n");
                goto error;
        }

        /* join the multicast group */
        result = join_mcast_group(sock->sk,
                        (struct in_addr *) &mcast_addr.sin_addr,
                        ip_vs_backup_mcast_ifn);
        if (result < 0) {
                IP_VS_ERR("Error joining to the multicast group\n");
                goto error;
        }

        return sock;

  error:
        sock_release(sock);
        return ERR_PTR(result);
}


static int
ip_vs_send_async(struct socket *sock, const char *buffer, const size_t length)
{
        struct msghdr        msg = {.msg_flags = MSG_DONTWAIT|MSG_NOSIGNAL};
        struct kvec        iov;
        int                len;

        EnterFunction(7);
        iov.iov_base     = (void *)buffer;
        iov.iov_len      = length;

        len = kernel_sendmsg(sock, &msg, &iov, 1, (size_t)(length));

        LeaveFunction(7);
        return len;
}

static void
ip_vs_send_sync_msg(struct socket *sock, struct ip_vs_sync_mesg *msg)
{
        int msize;

        msize = msg->size;

        /* Put size in network byte order */
        msg->size = htons(msg->size);

        if (ip_vs_send_async(sock, (char *)msg, msize) != msize)
                IP_VS_ERR("ip_vs_send_async error\n");
}

static int
ip_vs_receive(struct socket *sock, char *buffer, const size_t buflen)
{
        struct msghdr                msg = {NULL,};
        struct kvec                iov;
        int                        len;

        EnterFunction(7);

        /* Receive a packet */
        iov.iov_base     = buffer;
        iov.iov_len      = (size_t)buflen;

        len = kernel_recvmsg(sock, &msg, &iov, 1, buflen, 0);

        if (len < 0)
                return -1;

        LeaveFunction(7);
        return len;
}


static int sync_thread_master(void *data)
{
        struct ip_vs_sync_thread_data *tinfo = data;
        struct ip_vs_sync_buff *sb;

        IP_VS_INFO("sync thread started: state = MASTER, mcast_ifn = %s, "
                   "syncid = %d\n",
                   ip_vs_master_mcast_ifn, ip_vs_master_syncid);

        while (!kthread_should_stop()) {
                while ((sb = sb_dequeue())) {
                        ip_vs_send_sync_msg(tinfo->sock, sb->mesg);
                        ip_vs_sync_buff_release(sb);
                }

                /* check if entries stay in curr_sb for 2 seconds */
                sb = get_curr_sync_buff(2 * HZ);
                if (sb) {
                        ip_vs_send_sync_msg(tinfo->sock, sb->mesg);
                        ip_vs_sync_buff_release(sb);
                }

                schedule_timeout_interruptible(HZ);
        }

        /* clean up the sync_buff queue */
        while ((sb=sb_dequeue())) {
                ip_vs_sync_buff_release(sb);
        }

        /* clean up the current sync_buff */
        if ((sb = get_curr_sync_buff(0))) {
                ip_vs_sync_buff_release(sb);
        }

        /* release the sending multicast socket */
        sock_release(tinfo->sock);
        kfree(tinfo);

        return 0;
}


static int sync_thread_backup(void *data)
{
        struct ip_vs_sync_thread_data *tinfo = data;
        int len;

        IP_VS_INFO("sync thread started: state = BACKUP, mcast_ifn = %s, "
                   "syncid = %d\n",
                   ip_vs_backup_mcast_ifn, ip_vs_backup_syncid);

        while (!kthread_should_stop()) {
                wait_event_interruptible(*tinfo->sock->sk->sk_sleep,
                         !skb_queue_empty(&tinfo->sock->sk->sk_receive_queue)
                         || kthread_should_stop());

                /* do we have data now? */
                while (!skb_queue_empty(&(tinfo->sock->sk->sk_receive_queue))) {
                        len = ip_vs_receive(tinfo->sock, tinfo->buf,
                                        sync_recv_mesg_maxlen);
                        if (len <= 0) {
                                IP_VS_ERR("receiving message error\n");
                                break;
                        }

                        /* disable bottom half, because it accesses the data
                           shared by softirq while getting/creating conns */
                        local_bh_disable();
                        ip_vs_process_message(tinfo->buf, len);
                        local_bh_enable();
                }
        }

        /* release the sending multicast socket */
        sock_release(tinfo->sock);
        kfree(tinfo->buf);
        kfree(tinfo);

        return 0;
}


int start_sync_thread(int state, char *mcast_ifn, __u8 syncid)
{
        struct ip_vs_sync_thread_data *tinfo;
        struct task_struct **realtask, *task;
        struct socket *sock;
        char *name, *buf = NULL;
        int (*threadfn)(void *data);
        int result = -ENOMEM;

        IP_VS_DBG(7, "%s: pid %d\n", __func__, task_pid_nr(current));
        IP_VS_DBG(7, "Each ip_vs_sync_conn entry needs %Zd bytes\n",
                  sizeof(struct ip_vs_sync_conn));

        if (state == IP_VS_STATE_MASTER) {
                if (sync_master_thread)
                        return -EEXIST;

                strlcpy(ip_vs_master_mcast_ifn, mcast_ifn,
                        sizeof(ip_vs_master_mcast_ifn));
                ip_vs_master_syncid = syncid;
                realtask = &sync_master_thread;
                name = "ipvs_syncmaster";
                threadfn = sync_thread_master;
                sock = make_send_sock();
        } else if (state == IP_VS_STATE_BACKUP) {
                if (sync_backup_thread)
                        return -EEXIST;

                strlcpy(ip_vs_backup_mcast_ifn, mcast_ifn,
                        sizeof(ip_vs_backup_mcast_ifn));
                ip_vs_backup_syncid = syncid;
                realtask = &sync_backup_thread;
                name = "ipvs_syncbackup";
                threadfn = sync_thread_backup;
                sock = make_receive_sock();
        } else {
                return -EINVAL;
        }

        if (IS_ERR(sock)) {
                result = PTR_ERR(sock);
                goto out;
        }

        set_sync_mesg_maxlen(state);
        if (state == IP_VS_STATE_BACKUP) {
                buf = kmalloc(sync_recv_mesg_maxlen, GFP_KERNEL);
                if (!buf)
                        goto outsocket;
        }

        tinfo = kmalloc(sizeof(*tinfo), GFP_KERNEL);
        if (!tinfo)
                goto outbuf;

        tinfo->sock = sock;
        tinfo->buf = buf;

        task = kthread_run(threadfn, tinfo, name);
        if (IS_ERR(task)) {
                result = PTR_ERR(task);
                goto outtinfo;
        }

        /* mark as active */
        *realtask = task;
        ip_vs_sync_state |= state;

        /* increase the module use count */
        ip_vs_use_count_inc();

        return 0;

outtinfo:
        kfree(tinfo);
outbuf:
        kfree(buf);
outsocket:
        sock_release(sock);
out:
        return result;
}


int stop_sync_thread(int state)
{
        IP_VS_DBG(7, "%s: pid %d\n", __func__, task_pid_nr(current));

        if (state == IP_VS_STATE_MASTER) {
                if (!sync_master_thread)
                        return -ESRCH;

                IP_VS_INFO("stopping master sync thread %d ...\n",
                           task_pid_nr(sync_master_thread));

                /*
                 * The lock synchronizes with sb_queue_tail(), so that we don't
                 * add sync buffers to the queue, when we are already in
                 * progress of stopping the master sync daemon.
                 */

                spin_lock_bh(&ip_vs_sync_lock);
                ip_vs_sync_state &= ~IP_VS_STATE_MASTER;
                spin_unlock_bh(&ip_vs_sync_lock);
                kthread_stop(sync_master_thread);
                sync_master_thread = NULL;
        } else if (state == IP_VS_STATE_BACKUP) {
                if (!sync_backup_thread)
                        return -ESRCH;

                IP_VS_INFO("stopping backup sync thread %d ...\n",
                           task_pid_nr(sync_backup_thread));

                ip_vs_sync_state &= ~IP_VS_STATE_BACKUP;
                kthread_stop(sync_backup_thread);
                sync_backup_thread = NULL;
        } else {
                return -EINVAL;
        }

        /* decrease the module use count */
        ip_vs_use_count_dec();

        return 0;
}