Linux 4.19-rc7

[linux-2.6/btrfs-unstable.git] / net / rds / connection.c

/*
 * Copyright (c) 2006, 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - Redistributions in binary form must reproduce the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer in the documentation and/or other materials
 *        provided with the distribution.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 */
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <net/ipv6.h>
#include <net/inet6_hashtables.h>
#include <net/addrconf.h>

#include "rds.h"
#include "loop.h"

#define RDS_CONNECTION_HASH_BITS 12
#define RDS_CONNECTION_HASH_ENTRIES (1 << RDS_CONNECTION_HASH_BITS)
#define RDS_CONNECTION_HASH_MASK (RDS_CONNECTION_HASH_ENTRIES - 1)

/* converting this to RCU is a chore for another day.. */
static DEFINE_SPINLOCK(rds_conn_lock);
static unsigned long rds_conn_count;
static struct hlist_head rds_conn_hash[RDS_CONNECTION_HASH_ENTRIES];
static struct kmem_cache *rds_conn_slab;

static struct hlist_head *rds_conn_bucket(const struct in6_addr *laddr,
                                          const struct in6_addr *faddr)
{
        static u32 rds6_hash_secret __read_mostly;
        static u32 rds_hash_secret __read_mostly;

        u32 lhash, fhash, hash;

        net_get_random_once(&rds_hash_secret, sizeof(rds_hash_secret));
        net_get_random_once(&rds6_hash_secret, sizeof(rds6_hash_secret));

        lhash = (__force u32)laddr->s6_addr32[3];
#if IS_ENABLED(CONFIG_IPV6)
        fhash = __ipv6_addr_jhash(faddr, rds6_hash_secret);
#else
        fhash = (__force u32)faddr->s6_addr32[3];
#endif
        hash = __inet_ehashfn(lhash, 0, fhash, 0, rds_hash_secret);

        return &rds_conn_hash[hash & RDS_CONNECTION_HASH_MASK];
}

#define rds_conn_info_set(var, test, suffix) do {               \
        if (test)                                               \
                var |= RDS_INFO_CONNECTION_FLAG_##suffix;       \
} while (0)

/* rcu read lock must be held or the connection spinlock */
static struct rds_connection *rds_conn_lookup(struct net *net,
                                              struct hlist_head *head,
                                              const struct in6_addr *laddr,
                                              const struct in6_addr *faddr,
                                              struct rds_transport *trans,
                                              int dev_if)
{
        struct rds_connection *conn, *ret = NULL;

        hlist_for_each_entry_rcu(conn, head, c_hash_node) {
                if (ipv6_addr_equal(&conn->c_faddr, faddr) &&
                    ipv6_addr_equal(&conn->c_laddr, laddr) &&
                    conn->c_trans == trans &&
                    net == rds_conn_net(conn) &&
                    conn->c_dev_if == dev_if) {
                        ret = conn;
                        break;
                }
        }
        rdsdebug("returning conn %p for %pI6c -> %pI6c\n", ret,
                 laddr, faddr);
        return ret;
}

/*
 * This is called by transports as they're bringing down a connection.
 * It clears partial message state so that the transport can start sending
 * and receiving over this connection again in the future.  It is up to
 * the transport to have serialized this call with its send and recv.
 */
static void rds_conn_path_reset(struct rds_conn_path *cp)
{
        struct rds_connection *conn = cp->cp_conn;

        rdsdebug("connection %pI6c to %pI6c reset\n",
                 &conn->c_laddr, &conn->c_faddr);

        rds_stats_inc(s_conn_reset);
        rds_send_path_reset(cp);
        cp->cp_flags = 0;

        /* Do not clear next_rx_seq here, else we cannot distinguish
         * retransmitted packets from new packets, and will hand all
         * of them to the application. That is not consistent with the
         * reliability guarantees of RDS. */
}

static void __rds_conn_path_init(struct rds_connection *conn,
                                 struct rds_conn_path *cp, bool is_outgoing)
{
        spin_lock_init(&cp->cp_lock);
        cp->cp_next_tx_seq = 1;
        init_waitqueue_head(&cp->cp_waitq);
        INIT_LIST_HEAD(&cp->cp_send_queue);
        INIT_LIST_HEAD(&cp->cp_retrans);

        cp->cp_conn = conn;
        atomic_set(&cp->cp_state, RDS_CONN_DOWN);
        cp->cp_send_gen = 0;
        cp->cp_reconnect_jiffies = 0;
        INIT_DELAYED_WORK(&cp->cp_send_w, rds_send_worker);
        INIT_DELAYED_WORK(&cp->cp_recv_w, rds_recv_worker);
        INIT_DELAYED_WORK(&cp->cp_conn_w, rds_connect_worker);
        INIT_WORK(&cp->cp_down_w, rds_shutdown_worker);
        mutex_init(&cp->cp_cm_lock);
        cp->cp_flags = 0;
}

/*
 * There is only every one 'conn' for a given pair of addresses in the
 * system at a time.  They contain messages to be retransmitted and so
 * span the lifetime of the actual underlying transport connections.
 *
 * For now they are not garbage collected once they're created.  They
 * are torn down as the module is removed, if ever.
 */
static struct rds_connection *__rds_conn_create(struct net *net,
                                                const struct in6_addr *laddr,
                                                const struct in6_addr *faddr,
                                                struct rds_transport *trans,
                                                gfp_t gfp,
                                                int is_outgoing,
                                                int dev_if)
{
        struct rds_connection *conn, *parent = NULL;
        struct hlist_head *head = rds_conn_bucket(laddr, faddr);
        struct rds_transport *loop_trans;
        unsigned long flags;
        int ret, i;
        int npaths = (trans->t_mp_capable ? RDS_MPATH_WORKERS : 1);

        rcu_read_lock();
        conn = rds_conn_lookup(net, head, laddr, faddr, trans, dev_if);
        if (conn &&
            conn->c_loopback &&
            conn->c_trans != &rds_loop_transport &&
            ipv6_addr_equal(laddr, faddr) &&
            !is_outgoing) {
                /* This is a looped back IB connection, and we're
                 * called by the code handling the incoming connect.
                 * We need a second connection object into which we
                 * can stick the other QP. */
                parent = conn;
                conn = parent->c_passive;
        }
        rcu_read_unlock();
        if (conn)
                goto out;

        conn = kmem_cache_zalloc(rds_conn_slab, gfp);
        if (!conn) {
                conn = ERR_PTR(-ENOMEM);
                goto out;
        }
        conn->c_path = kcalloc(npaths, sizeof(struct rds_conn_path), gfp);
        if (!conn->c_path) {
                kmem_cache_free(rds_conn_slab, conn);
                conn = ERR_PTR(-ENOMEM);
                goto out;
        }

        INIT_HLIST_NODE(&conn->c_hash_node);
        conn->c_laddr = *laddr;
        conn->c_isv6 = !ipv6_addr_v4mapped(laddr);
        conn->c_faddr = *faddr;
        conn->c_dev_if = dev_if;

#if IS_ENABLED(CONFIG_IPV6)
        /* If the local address is link local, set c_bound_if to be the
         * index used for this connection.  Otherwise, set it to 0 as
         * the socket is not bound to an interface.  c_bound_if is used
         * to look up a socket when a packet is received
         */
        if (ipv6_addr_type(laddr) & IPV6_ADDR_LINKLOCAL)
                conn->c_bound_if = dev_if;
        else
#endif
                conn->c_bound_if = 0;

        rds_conn_net_set(conn, net);

        ret = rds_cong_get_maps(conn);
        if (ret) {
                kfree(conn->c_path);
                kmem_cache_free(rds_conn_slab, conn);
                conn = ERR_PTR(ret);
                goto out;
        }

        /*
         * This is where a connection becomes loopback.  If *any* RDS sockets
         * can bind to the destination address then we'd rather the messages
         * flow through loopback rather than either transport.
         */
        loop_trans = rds_trans_get_preferred(net, faddr, conn->c_dev_if);
        if (loop_trans) {
                rds_trans_put(loop_trans);
                conn->c_loopback = 1;
                if (is_outgoing && trans->t_prefer_loopback) {
                        /* "outgoing" connection - and the transport
                         * says it wants the connection handled by the
                         * loopback transport. This is what TCP does.
                         */
                        trans = &rds_loop_transport;
                }
        }

        conn->c_trans = trans;

        init_waitqueue_head(&conn->c_hs_waitq);
        for (i = 0; i < npaths; i++) {
                __rds_conn_path_init(conn, &conn->c_path[i],
                                     is_outgoing);
                conn->c_path[i].cp_index = i;
        }
        rcu_read_lock();
        if (rds_destroy_pending(conn))
                ret = -ENETDOWN;
        else
                ret = trans->conn_alloc(conn, GFP_ATOMIC);
        if (ret) {
                rcu_read_unlock();
                kfree(conn->c_path);
                kmem_cache_free(rds_conn_slab, conn);
                conn = ERR_PTR(ret);
                goto out;
        }

        rdsdebug("allocated conn %p for %pI6c -> %pI6c over %s %s\n",
                 conn, laddr, faddr,
                 strnlen(trans->t_name, sizeof(trans->t_name)) ?
                 trans->t_name : "[unknown]", is_outgoing ? "(outgoing)" : "");

        /*
         * Since we ran without holding the conn lock, someone could
         * have created the same conn (either normal or passive) in the
         * interim. We check while holding the lock. If we won, we complete
         * init and return our conn. If we lost, we rollback and return the
         * other one.
         */
        spin_lock_irqsave(&rds_conn_lock, flags);
        if (parent) {
                /* Creating passive conn */
                if (parent->c_passive) {
                        trans->conn_free(conn->c_path[0].cp_transport_data);
                        kfree(conn->c_path);
                        kmem_cache_free(rds_conn_slab, conn);
                        conn = parent->c_passive;
                } else {
                        parent->c_passive = conn;
                        rds_cong_add_conn(conn);
                        rds_conn_count++;
                }
        } else {
                /* Creating normal conn */
                struct rds_connection *found;

                found = rds_conn_lookup(net, head, laddr, faddr, trans,
                                        dev_if);
                if (found) {
                        struct rds_conn_path *cp;
                        int i;

                        for (i = 0; i < npaths; i++) {
                                cp = &conn->c_path[i];
                                /* The ->conn_alloc invocation may have
                                 * allocated resource for all paths, so all
                                 * of them may have to be freed here.
                                 */
                                if (cp->cp_transport_data)
                                        trans->conn_free(cp->cp_transport_data);
                        }
                        kfree(conn->c_path);
                        kmem_cache_free(rds_conn_slab, conn);
                        conn = found;
                } else {
                        conn->c_my_gen_num = rds_gen_num;
                        conn->c_peer_gen_num = 0;
                        hlist_add_head_rcu(&conn->c_hash_node, head);
                        rds_cong_add_conn(conn);
                        rds_conn_count++;
                }
        }
        spin_unlock_irqrestore(&rds_conn_lock, flags);
        rcu_read_unlock();

out:
        return conn;
}

struct rds_connection *rds_conn_create(struct net *net,
                                       const struct in6_addr *laddr,
                                       const struct in6_addr *faddr,
                                       struct rds_transport *trans, gfp_t gfp,
                                       int dev_if)
{
        return __rds_conn_create(net, laddr, faddr, trans, gfp, 0, dev_if);
}
EXPORT_SYMBOL_GPL(rds_conn_create);

struct rds_connection *rds_conn_create_outgoing(struct net *net,
                                                const struct in6_addr *laddr,
                                                const struct in6_addr *faddr,
                                                struct rds_transport *trans,
                                                gfp_t gfp, int dev_if)
{
        return __rds_conn_create(net, laddr, faddr, trans, gfp, 1, dev_if);
}
EXPORT_SYMBOL_GPL(rds_conn_create_outgoing);

void rds_conn_shutdown(struct rds_conn_path *cp)
{
        struct rds_connection *conn = cp->cp_conn;

        /* shut it down unless it's down already */
        if (!rds_conn_path_transition(cp, RDS_CONN_DOWN, RDS_CONN_DOWN)) {
                /*
                 * Quiesce the connection mgmt handlers before we start tearing
                 * things down. We don't hold the mutex for the entire
                 * duration of the shutdown operation, else we may be
                 * deadlocking with the CM handler. Instead, the CM event
                 * handler is supposed to check for state DISCONNECTING
                 */
                mutex_lock(&cp->cp_cm_lock);
                if (!rds_conn_path_transition(cp, RDS_CONN_UP,
                                              RDS_CONN_DISCONNECTING) &&
                    !rds_conn_path_transition(cp, RDS_CONN_ERROR,
                                              RDS_CONN_DISCONNECTING)) {
                        rds_conn_path_error(cp,
                                            "shutdown called in state %d\n",
                                            atomic_read(&cp->cp_state));
                        mutex_unlock(&cp->cp_cm_lock);
                        return;
                }
                mutex_unlock(&cp->cp_cm_lock);

                wait_event(cp->cp_waitq,
                           !test_bit(RDS_IN_XMIT, &cp->cp_flags));
                wait_event(cp->cp_waitq,
                           !test_bit(RDS_RECV_REFILL, &cp->cp_flags));

                conn->c_trans->conn_path_shutdown(cp);
                rds_conn_path_reset(cp);

                if (!rds_conn_path_transition(cp, RDS_CONN_DISCONNECTING,
                                              RDS_CONN_DOWN) &&
                    !rds_conn_path_transition(cp, RDS_CONN_ERROR,
                                              RDS_CONN_DOWN)) {
                        /* This can happen - eg when we're in the middle of tearing
                         * down the connection, and someone unloads the rds module.
                         * Quite reproducible with loopback connections.
                         * Mostly harmless.
                         *
                         * Note that this also happens with rds-tcp because
                         * we could have triggered rds_conn_path_drop in irq
                         * mode from rds_tcp_state change on the receipt of
                         * a FIN, thus we need to recheck for RDS_CONN_ERROR
                         * here.
                         */
                        rds_conn_path_error(cp, "%s: failed to transition "
                                            "to state DOWN, current state "
                                            "is %d\n", __func__,
                                            atomic_read(&cp->cp_state));
                        return;
                }
        }

        /* Then reconnect if it's still live.
         * The passive side of an IB loopback connection is never added
         * to the conn hash, so we never trigger a reconnect on this
         * conn - the reconnect is always triggered by the active peer. */
        cancel_delayed_work_sync(&cp->cp_conn_w);
        rcu_read_lock();
        if (!hlist_unhashed(&conn->c_hash_node)) {
                rcu_read_unlock();
                rds_queue_reconnect(cp);
        } else {
                rcu_read_unlock();
        }
}

/* destroy a single rds_conn_path. rds_conn_destroy() iterates over
 * all paths using rds_conn_path_destroy()
 */
static void rds_conn_path_destroy(struct rds_conn_path *cp)
{
        struct rds_message *rm, *rtmp;

        if (!cp->cp_transport_data)
                return;

        /* make sure lingering queued work won't try to ref the conn */
        cancel_delayed_work_sync(&cp->cp_send_w);
        cancel_delayed_work_sync(&cp->cp_recv_w);

        rds_conn_path_drop(cp, true);
        flush_work(&cp->cp_down_w);

        /* tear down queued messages */
        list_for_each_entry_safe(rm, rtmp,
                                 &cp->cp_send_queue,
                                 m_conn_item) {
                list_del_init(&rm->m_conn_item);
                BUG_ON(!list_empty(&rm->m_sock_item));
                rds_message_put(rm);
        }
        if (cp->cp_xmit_rm)
                rds_message_put(cp->cp_xmit_rm);

        WARN_ON(delayed_work_pending(&cp->cp_send_w));
        WARN_ON(delayed_work_pending(&cp->cp_recv_w));
        WARN_ON(delayed_work_pending(&cp->cp_conn_w));
        WARN_ON(work_pending(&cp->cp_down_w));

        cp->cp_conn->c_trans->conn_free(cp->cp_transport_data);
}

/*
 * Stop and free a connection.
 *
 * This can only be used in very limited circumstances.  It assumes that once
 * the conn has been shutdown that no one else is referencing the connection.
 * We can only ensure this in the rmmod path in the current code.
 */
void rds_conn_destroy(struct rds_connection *conn)
{
        unsigned long flags;
        int i;
        struct rds_conn_path *cp;
        int npaths = (conn->c_trans->t_mp_capable ? RDS_MPATH_WORKERS : 1);

        rdsdebug("freeing conn %p for %pI4 -> "
                 "%pI4\n", conn, &conn->c_laddr,
                 &conn->c_faddr);

        /* Ensure conn will not be scheduled for reconnect */
        spin_lock_irq(&rds_conn_lock);
        hlist_del_init_rcu(&conn->c_hash_node);
        spin_unlock_irq(&rds_conn_lock);
        synchronize_rcu();

        /* shut the connection down */
        for (i = 0; i < npaths; i++) {
                cp = &conn->c_path[i];
                rds_conn_path_destroy(cp);
                BUG_ON(!list_empty(&cp->cp_retrans));
        }

        /*
         * The congestion maps aren't freed up here.  They're
         * freed by rds_cong_exit() after all the connections
         * have been freed.
         */
        rds_cong_remove_conn(conn);

        kfree(conn->c_path);
        kmem_cache_free(rds_conn_slab, conn);

        spin_lock_irqsave(&rds_conn_lock, flags);
        rds_conn_count--;
        spin_unlock_irqrestore(&rds_conn_lock, flags);
}
EXPORT_SYMBOL_GPL(rds_conn_destroy);

static void __rds_inc_msg_cp(struct rds_incoming *inc,
                             struct rds_info_iterator *iter,
                             void *saddr, void *daddr, int flip, bool isv6)
{
#if IS_ENABLED(CONFIG_IPV6)
        if (isv6)
                rds6_inc_info_copy(inc, iter, saddr, daddr, flip);
        else
#endif
                rds_inc_info_copy(inc, iter, *(__be32 *)saddr,
                                  *(__be32 *)daddr, flip);
}

static void rds_conn_message_info_cmn(struct socket *sock, unsigned int len,
                                      struct rds_info_iterator *iter,
                                      struct rds_info_lengths *lens,
                                      int want_send, bool isv6)
{
        struct hlist_head *head;
        struct list_head *list;
        struct rds_connection *conn;
        struct rds_message *rm;
        unsigned int total = 0;
        unsigned long flags;
        size_t i;
        int j;

        if (isv6)
                len /= sizeof(struct rds6_info_message);
        else
                len /= sizeof(struct rds_info_message);

        rcu_read_lock();

        for (i = 0, head = rds_conn_hash; i < ARRAY_SIZE(rds_conn_hash);
             i++, head++) {
                hlist_for_each_entry_rcu(conn, head, c_hash_node) {
                        struct rds_conn_path *cp;
                        int npaths;

                        if (!isv6 && conn->c_isv6)
                                continue;

                        npaths = (conn->c_trans->t_mp_capable ?
                                 RDS_MPATH_WORKERS : 1);

                        for (j = 0; j < npaths; j++) {
                                cp = &conn->c_path[j];
                                if (want_send)
                                        list = &cp->cp_send_queue;
                                else
                                        list = &cp->cp_retrans;

                                spin_lock_irqsave(&cp->cp_lock, flags);

                                /* XXX too lazy to maintain counts.. */
                                list_for_each_entry(rm, list, m_conn_item) {
                                        total++;
                                        if (total <= len)
                                                __rds_inc_msg_cp(&rm->m_inc,
                                                                 iter,
                                                                 &conn->c_laddr,
                                                                 &conn->c_faddr,
                                                                 0, isv6);
                                }

                                spin_unlock_irqrestore(&cp->cp_lock, flags);
                        }
                }
        }
        rcu_read_unlock();

        lens->nr = total;
        if (isv6)
                lens->each = sizeof(struct rds6_info_message);
        else
                lens->each = sizeof(struct rds_info_message);
}

static void rds_conn_message_info(struct socket *sock, unsigned int len,
                                  struct rds_info_iterator *iter,
                                  struct rds_info_lengths *lens,
                                  int want_send)
{
        rds_conn_message_info_cmn(sock, len, iter, lens, want_send, false);
}

#if IS_ENABLED(CONFIG_IPV6)
static void rds6_conn_message_info(struct socket *sock, unsigned int len,
                                   struct rds_info_iterator *iter,
                                   struct rds_info_lengths *lens,
                                   int want_send)
{
        rds_conn_message_info_cmn(sock, len, iter, lens, want_send, true);
}
#endif

static void rds_conn_message_info_send(struct socket *sock, unsigned int len,
                                       struct rds_info_iterator *iter,
                                       struct rds_info_lengths *lens)
{
        rds_conn_message_info(sock, len, iter, lens, 1);
}

#if IS_ENABLED(CONFIG_IPV6)
static void rds6_conn_message_info_send(struct socket *sock, unsigned int len,
                                        struct rds_info_iterator *iter,
                                        struct rds_info_lengths *lens)
{
        rds6_conn_message_info(sock, len, iter, lens, 1);
}
#endif

static void rds_conn_message_info_retrans(struct socket *sock,
                                          unsigned int len,
                                          struct rds_info_iterator *iter,
                                          struct rds_info_lengths *lens)
{
        rds_conn_message_info(sock, len, iter, lens, 0);
}

#if IS_ENABLED(CONFIG_IPV6)
static void rds6_conn_message_info_retrans(struct socket *sock,
                                           unsigned int len,
                                           struct rds_info_iterator *iter,
                                           struct rds_info_lengths *lens)
{
        rds6_conn_message_info(sock, len, iter, lens, 0);
}
#endif

void rds_for_each_conn_info(struct socket *sock, unsigned int len,
                          struct rds_info_iterator *iter,
                          struct rds_info_lengths *lens,
                          int (*visitor)(struct rds_connection *, void *),
                          u64 *buffer,
                          size_t item_len)
{
        struct hlist_head *head;
        struct rds_connection *conn;
        size_t i;

        rcu_read_lock();

        lens->nr = 0;
        lens->each = item_len;

        for (i = 0, head = rds_conn_hash; i < ARRAY_SIZE(rds_conn_hash);
             i++, head++) {
                hlist_for_each_entry_rcu(conn, head, c_hash_node) {

                        /* XXX no c_lock usage.. */
                        if (!visitor(conn, buffer))
                                continue;

                        /* We copy as much as we can fit in the buffer,
                         * but we count all items so that the caller
                         * can resize the buffer. */
                        if (len >= item_len) {
                                rds_info_copy(iter, buffer, item_len);
                                len -= item_len;
                        }
                        lens->nr++;
                }
        }
        rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(rds_for_each_conn_info);

static void rds_walk_conn_path_info(struct socket *sock, unsigned int len,
                                    struct rds_info_iterator *iter,
                                    struct rds_info_lengths *lens,
                                    int (*visitor)(struct rds_conn_path *, void *),
                                    u64 *buffer,
                                    size_t item_len)
{
        struct hlist_head *head;
        struct rds_connection *conn;
        size_t i;

        rcu_read_lock();

        lens->nr = 0;
        lens->each = item_len;

        for (i = 0, head = rds_conn_hash; i < ARRAY_SIZE(rds_conn_hash);
             i++, head++) {
                hlist_for_each_entry_rcu(conn, head, c_hash_node) {
                        struct rds_conn_path *cp;

                        /* XXX We only copy the information from the first
                         * path for now.  The problem is that if there are
                         * more than one underlying paths, we cannot report
                         * information of all of them using the existing
                         * API.  For example, there is only one next_tx_seq,
                         * which path's next_tx_seq should we report?  It is
                         * a bug in the design of MPRDS.
                         */
                        cp = conn->c_path;

                        /* XXX no cp_lock usage.. */
                        if (!visitor(cp, buffer))
                                continue;

                        /* We copy as much as we can fit in the buffer,
                         * but we count all items so that the caller
                         * can resize the buffer.
                         */
                        if (len >= item_len) {
                                rds_info_copy(iter, buffer, item_len);
                                len -= item_len;
                        }
                        lens->nr++;
                }
        }
        rcu_read_unlock();
}

static int rds_conn_info_visitor(struct rds_conn_path *cp, void *buffer)
{
        struct rds_info_connection *cinfo = buffer;
        struct rds_connection *conn = cp->cp_conn;

        if (conn->c_isv6)
                return 0;

        cinfo->next_tx_seq = cp->cp_next_tx_seq;
        cinfo->next_rx_seq = cp->cp_next_rx_seq;
        cinfo->laddr = conn->c_laddr.s6_addr32[3];
        cinfo->faddr = conn->c_faddr.s6_addr32[3];
        strncpy(cinfo->transport, conn->c_trans->t_name,
                sizeof(cinfo->transport));
        cinfo->flags = 0;

        rds_conn_info_set(cinfo->flags, test_bit(RDS_IN_XMIT, &cp->cp_flags),
                          SENDING);
        /* XXX Future: return the state rather than these funky bits */
        rds_conn_info_set(cinfo->flags,
                          atomic_read(&cp->cp_state) == RDS_CONN_CONNECTING,
                          CONNECTING);
        rds_conn_info_set(cinfo->flags,
                          atomic_read(&cp->cp_state) == RDS_CONN_UP,
                          CONNECTED);
        return 1;
}

#if IS_ENABLED(CONFIG_IPV6)
static int rds6_conn_info_visitor(struct rds_conn_path *cp, void *buffer)
{
        struct rds6_info_connection *cinfo6 = buffer;
        struct rds_connection *conn = cp->cp_conn;

        cinfo6->next_tx_seq = cp->cp_next_tx_seq;
        cinfo6->next_rx_seq = cp->cp_next_rx_seq;
        cinfo6->laddr = conn->c_laddr;
        cinfo6->faddr = conn->c_faddr;
        strncpy(cinfo6->transport, conn->c_trans->t_name,
                sizeof(cinfo6->transport));
        cinfo6->flags = 0;

        rds_conn_info_set(cinfo6->flags, test_bit(RDS_IN_XMIT, &cp->cp_flags),
                          SENDING);
        /* XXX Future: return the state rather than these funky bits */
        rds_conn_info_set(cinfo6->flags,
                          atomic_read(&cp->cp_state) == RDS_CONN_CONNECTING,
                          CONNECTING);
        rds_conn_info_set(cinfo6->flags,
                          atomic_read(&cp->cp_state) == RDS_CONN_UP,
                          CONNECTED);
        /* Just return 1 as there is no error case. This is a helper function
         * for rds_walk_conn_path_info() and it wants a return value.
         */
        return 1;
}
#endif

static void rds_conn_info(struct socket *sock, unsigned int len,
                          struct rds_info_iterator *iter,
                          struct rds_info_lengths *lens)
{
        u64 buffer[(sizeof(struct rds_info_connection) + 7) / 8];

        rds_walk_conn_path_info(sock, len, iter, lens,
                                rds_conn_info_visitor,
                                buffer,
                                sizeof(struct rds_info_connection));
}

#if IS_ENABLED(CONFIG_IPV6)
static void rds6_conn_info(struct socket *sock, unsigned int len,
                           struct rds_info_iterator *iter,
                           struct rds_info_lengths *lens)
{
        u64 buffer[(sizeof(struct rds6_info_connection) + 7) / 8];

        rds_walk_conn_path_info(sock, len, iter, lens,
                                rds6_conn_info_visitor,
                                buffer,
                                sizeof(struct rds6_info_connection));
}
#endif

int rds_conn_init(void)
{
        int ret;

        ret = rds_loop_net_init(); /* register pernet callback */
        if (ret)
                return ret;

        rds_conn_slab = kmem_cache_create("rds_connection",
                                          sizeof(struct rds_connection),
                                          0, 0, NULL);
        if (!rds_conn_slab) {
                rds_loop_net_exit();
                return -ENOMEM;
        }

        rds_info_register_func(RDS_INFO_CONNECTIONS, rds_conn_info);
        rds_info_register_func(RDS_INFO_SEND_MESSAGES,
                               rds_conn_message_info_send);
        rds_info_register_func(RDS_INFO_RETRANS_MESSAGES,
                               rds_conn_message_info_retrans);
#if IS_ENABLED(CONFIG_IPV6)
        rds_info_register_func(RDS6_INFO_CONNECTIONS, rds6_conn_info);
        rds_info_register_func(RDS6_INFO_SEND_MESSAGES,
                               rds6_conn_message_info_send);
        rds_info_register_func(RDS6_INFO_RETRANS_MESSAGES,
                               rds6_conn_message_info_retrans);
#endif
        return 0;
}

void rds_conn_exit(void)
{
        rds_loop_net_exit(); /* unregister pernet callback */
        rds_loop_exit();

        WARN_ON(!hlist_empty(rds_conn_hash));

        kmem_cache_destroy(rds_conn_slab);

        rds_info_deregister_func(RDS_INFO_CONNECTIONS, rds_conn_info);
        rds_info_deregister_func(RDS_INFO_SEND_MESSAGES,
                                 rds_conn_message_info_send);
        rds_info_deregister_func(RDS_INFO_RETRANS_MESSAGES,
                                 rds_conn_message_info_retrans);
#if IS_ENABLED(CONFIG_IPV6)
        rds_info_deregister_func(RDS6_INFO_CONNECTIONS, rds6_conn_info);
        rds_info_deregister_func(RDS6_INFO_SEND_MESSAGES,
                                 rds6_conn_message_info_send);
        rds_info_deregister_func(RDS6_INFO_RETRANS_MESSAGES,
                                 rds6_conn_message_info_retrans);
#endif
}

/*
 * Force a disconnect
 */
void rds_conn_path_drop(struct rds_conn_path *cp, bool destroy)
{
        atomic_set(&cp->cp_state, RDS_CONN_ERROR);

        rcu_read_lock();
        if (!destroy && rds_destroy_pending(cp->cp_conn)) {
                rcu_read_unlock();
                return;
        }
        queue_work(rds_wq, &cp->cp_down_w);
        rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(rds_conn_path_drop);

void rds_conn_drop(struct rds_connection *conn)
{
        WARN_ON(conn->c_trans->t_mp_capable);
        rds_conn_path_drop(&conn->c_path[0], false);
}
EXPORT_SYMBOL_GPL(rds_conn_drop);

/*
 * If the connection is down, trigger a connect. We may have scheduled a
 * delayed reconnect however - in this case we should not interfere.
 */
void rds_conn_path_connect_if_down(struct rds_conn_path *cp)
{
        rcu_read_lock();
        if (rds_destroy_pending(cp->cp_conn)) {
                rcu_read_unlock();
                return;
        }
        if (rds_conn_path_state(cp) == RDS_CONN_DOWN &&
            !test_and_set_bit(RDS_RECONNECT_PENDING, &cp->cp_flags))
                queue_delayed_work(rds_wq, &cp->cp_conn_w, 0);
        rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(rds_conn_path_connect_if_down);

void rds_conn_connect_if_down(struct rds_connection *conn)
{
        WARN_ON(conn->c_trans->t_mp_capable);
        rds_conn_path_connect_if_down(&conn->c_path[0]);
}
EXPORT_SYMBOL_GPL(rds_conn_connect_if_down);

void
__rds_conn_path_error(struct rds_conn_path *cp, const char *fmt, ...)
{
        va_list ap;

        va_start(ap, fmt);
        vprintk(fmt, ap);
        va_end(ap);

        rds_conn_path_drop(cp, false);
}