ofproto: Move bond files to ofproto

Relocating bond.[ch] to allow bond.c to make ofproto calls.
This is needed for upcoming patches that enable megaflow support
for bond ports.

Signed-off-by: Andy Zhou <azhou@nicira.com>

1 files changed, 1560 insertions, 0 deletions

diff --git a/ofproto/bond.c b/ofproto/bond.c
new file mode 100644
index 000000000..dc0d76b58
--- /dev/null
+++ b/ofproto/bond.c
@@ -0,0 +1,1560 @@
+/*
+ * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <config.h>
+
+#include "bond.h"
+
+#include <limits.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <math.h>
+
+#include "coverage.h"
+#include "dynamic-string.h"
+#include "flow.h"
+#include "hmap.h"
+#include "lacp.h"
+#include "list.h"
+#include "netdev.h"
+#include "odp-util.h"
+#include "ofpbuf.h"
+#include "packets.h"
+#include "poll-loop.h"
+#include "shash.h"
+#include "timeval.h"
+#include "unixctl.h"
+#include "vlog.h"
+
+VLOG_DEFINE_THIS_MODULE(bond);
+
+/* Bit-mask for hashing a flow down to a bucket.
+ * There are (BOND_MASK + 1) buckets. */
+#define BOND_MASK 0xff
+
+/* A hash bucket for mapping a flow to a slave.
+ * "struct bond" has an array of (BOND_MASK + 1) of these. */
+struct bond_entry {
+    struct bond_slave *slave;   /* Assigned slave, NULL if unassigned. */
+    uint64_t tx_bytes;          /* Count of bytes recently transmitted. */
+    struct list list_node;      /* In bond_slave's 'entries' list. */
+};
+
+/* A bond slave, that is, one of the links comprising a bond. */
+struct bond_slave {
+    struct hmap_node hmap_node; /* In struct bond's slaves hmap. */
+    struct bond *bond;          /* The bond that contains this slave. */
+    void *aux;                  /* Client-provided handle for this slave. */
+
+    struct netdev *netdev;      /* Network device, owned by the client. */
+    unsigned int change_seq;    /* Tracks changes in 'netdev'. */
+    char *name;                 /* Name (a copy of netdev_get_name(netdev)). */
+
+    /* Link status. */
+    long long delay_expires;    /* Time after which 'enabled' may change. */
+    bool enabled;               /* May be chosen for flows? */
+    bool may_enable;            /* Client considers this slave bondable. */
+
+    /* Rebalancing info.  Used only by bond_rebalance(). */
+    struct list bal_node;       /* In bond_rebalance()'s 'bals' list. */
+    struct list entries;        /* 'struct bond_entry's assigned here. */
+    uint64_t tx_bytes;          /* Sum across 'tx_bytes' of entries. */
+};
+
+/* A bond, that is, a set of network devices grouped to improve performance or
+ * robustness.  */
+struct bond {
+    struct hmap_node hmap_node; /* In 'all_bonds' hmap. */
+    char *name;                 /* Name provided by client. */
+
+    /* Slaves. */
+    struct hmap slaves;
+
+    /* Bonding info. */
+    enum bond_mode balance;     /* Balancing mode, one of BM_*. */
+    struct bond_slave *active_slave;
+    int updelay, downdelay;     /* Delay before slave goes up/down, in ms. */
+    enum lacp_status lacp_status; /* Status of LACP negotiations. */
+    bool bond_revalidate;       /* True if flows need revalidation. */
+    uint32_t basis;             /* Basis for flow hash function. */
+
+    /* SLB specific bonding info. */
+    struct bond_entry *hash;     /* An array of (BOND_MASK + 1) elements. */
+    int rebalance_interval;      /* Interval between rebalances, in ms. */
+    long long int next_rebalance; /* Next rebalancing time. */
+    bool send_learning_packets;
+
+    /* Legacy compatibility. */
+    long long int next_fake_iface_update; /* LLONG_MAX if disabled. */
+    bool lacp_fallback_ab; /* Fallback to active-backup on LACP failure. */
+
+    atomic_int ref_cnt;
+};
+
+static struct ovs_rwlock rwlock = OVS_RWLOCK_INITIALIZER;
+static struct hmap all_bonds__ = HMAP_INITIALIZER(&all_bonds__);
+static struct hmap *const all_bonds OVS_GUARDED_BY(rwlock) = &all_bonds__;
+
+static void bond_entry_reset(struct bond *) OVS_REQ_WRLOCK(rwlock);
+static struct bond_slave *bond_slave_lookup(struct bond *, const void *slave_)
+    OVS_REQ_RDLOCK(rwlock);
+static void bond_enable_slave(struct bond_slave *, bool enable)
+    OVS_REQ_WRLOCK(rwlock);
+static void bond_link_status_update(struct bond_slave *)
+    OVS_REQ_WRLOCK(rwlock);
+static void bond_choose_active_slave(struct bond *)
+    OVS_REQ_WRLOCK(rwlock);;
+static unsigned int bond_hash_src(const uint8_t mac[ETH_ADDR_LEN],
+                                  uint16_t vlan, uint32_t basis);
+static unsigned int bond_hash_tcp(const struct flow *, uint16_t vlan,
+                                  uint32_t basis);
+static struct bond_entry *lookup_bond_entry(const struct bond *,
+                                            const struct flow *,
+                                            uint16_t vlan)
+    OVS_REQ_RDLOCK(rwlock);
+static struct bond_slave *choose_output_slave(const struct bond *,
+                                              const struct flow *,
+                                              struct flow_wildcards *,
+                                              uint16_t vlan)
+    OVS_REQ_RDLOCK(rwlock);
+static void bond_update_fake_slave_stats(struct bond *)
+    OVS_REQ_RDLOCK(rwlock);
+
+/* Attempts to parse 's' as the name of a bond balancing mode.  If successful,
+ * stores the mode in '*balance' and returns true.  Otherwise returns false
+ * without modifying '*balance'. */
+bool
+bond_mode_from_string(enum bond_mode *balance, const char *s)
+{
+    if (!strcmp(s, bond_mode_to_string(BM_TCP))) {
+        *balance = BM_TCP;
+    } else if (!strcmp(s, bond_mode_to_string(BM_SLB))) {
+        *balance = BM_SLB;
+    } else if (!strcmp(s, bond_mode_to_string(BM_AB))) {
+        *balance = BM_AB;
+    } else {
+        return false;
+    }
+    return true;
+}
+
+/* Returns a string representing 'balance'. */
+const char *
+bond_mode_to_string(enum bond_mode balance) {
+    switch (balance) {
+    case BM_TCP:
+        return "balance-tcp";
+    case BM_SLB:
+        return "balance-slb";
+    case BM_AB:
+        return "active-backup";
+    }
+    NOT_REACHED();
+}
+
+
+/* Creates and returns a new bond whose configuration is initially taken from
+ * 's'.
+ *
+ * The caller should register each slave on the new bond by calling
+ * bond_slave_register().  */
+struct bond *
+bond_create(const struct bond_settings *s)
+{
+    struct bond *bond;
+
+    bond = xzalloc(sizeof *bond);
+    hmap_init(&bond->slaves);
+    bond->next_fake_iface_update = LLONG_MAX;
+    atomic_init(&bond->ref_cnt, 1);
+
+    bond_reconfigure(bond, s);
+    return bond;
+}
+
+struct bond *
+bond_ref(const struct bond *bond_)
+{
+    struct bond *bond = CONST_CAST(struct bond *, bond_);
+
+    if (bond) {
+        int orig;
+        atomic_add(&bond->ref_cnt, 1, &orig);
+        ovs_assert(orig > 0);
+    }
+    return bond;
+}
+
+/* Frees 'bond'. */
+void
+bond_unref(struct bond *bond)
+{
+    struct bond_slave *slave, *next_slave;
+    int orig;
+
+    if (!bond) {
+        return;
+    }
+
+    atomic_sub(&bond->ref_cnt, 1, &orig);
+    ovs_assert(orig > 0);
+    if (orig != 1) {
+        return;
+    }
+
+    ovs_rwlock_wrlock(&rwlock);
+    hmap_remove(all_bonds, &bond->hmap_node);
+    ovs_rwlock_unlock(&rwlock);
+
+    HMAP_FOR_EACH_SAFE (slave, next_slave, hmap_node, &bond->slaves) {
+        hmap_remove(&bond->slaves, &slave->hmap_node);
+        /* Client owns 'slave->netdev'. */
+        free(slave->name);
+        free(slave);
+    }
+    hmap_destroy(&bond->slaves);
+
+    free(bond->hash);
+    free(bond->name);
+    free(bond);
+}
+
+/* Updates 'bond''s overall configuration to 's'.
+ *
+ * The caller should register each slave on 'bond' by calling
+ * bond_slave_register().  This is optional if none of the slaves'
+ * configuration has changed.  In any case it can't hurt.
+ *
+ * Returns true if the configuration has changed in such a way that requires
+ * flow revalidation.
+ * */
+bool
+bond_reconfigure(struct bond *bond, const struct bond_settings *s)
+{
+    bool revalidate = false;
+
+    ovs_rwlock_wrlock(&rwlock);
+    if (!bond->name || strcmp(bond->name, s->name)) {
+        if (bond->name) {
+            hmap_remove(all_bonds, &bond->hmap_node);
+            free(bond->name);
+        }
+        bond->name = xstrdup(s->name);
+        hmap_insert(all_bonds, &bond->hmap_node, hash_string(bond->name, 0));
+    }
+
+    bond->updelay = s->up_delay;
+    bond->downdelay = s->down_delay;
+
+    if (bond->lacp_fallback_ab != s->lacp_fallback_ab_cfg) {
+        bond->lacp_fallback_ab = s->lacp_fallback_ab_cfg;
+        revalidate = true;
+    }
+
+    if (bond->rebalance_interval != s->rebalance_interval) {
+        bond->rebalance_interval = s->rebalance_interval;
+        revalidate = true;
+    }
+
+    if (bond->balance != s->balance) {
+        bond->balance = s->balance;
+        revalidate = true;
+    }
+
+    if (bond->basis != s->basis) {
+        bond->basis = s->basis;
+        revalidate = true;
+    }
+
+    if (s->fake_iface) {
+        if (bond->next_fake_iface_update == LLONG_MAX) {
+            bond->next_fake_iface_update = time_msec();
+        }
+    } else {
+        bond->next_fake_iface_update = LLONG_MAX;
+    }
+
+    if (bond->bond_revalidate) {
+        revalidate = true;
+        bond->bond_revalidate = false;
+    }
+
+    if (bond->balance == BM_AB || !bond->hash || revalidate) {
+        bond_entry_reset(bond);
+    }
+
+    ovs_rwlock_unlock(&rwlock);
+    return revalidate;
+}
+
+static void
+bond_slave_set_netdev__(struct bond_slave *slave, struct netdev *netdev)
+    OVS_REQ_WRLOCK(rwlock)
+{
+    if (slave->netdev != netdev) {
+        slave->netdev = netdev;
+        slave->change_seq = 0;
+    }
+}
+
+/* Registers 'slave_' as a slave of 'bond'.  The 'slave_' pointer is an
+ * arbitrary client-provided pointer that uniquely identifies a slave within a
+ * bond.  If 'slave_' already exists within 'bond' then this function
+ * reconfigures the existing slave.
+ *
+ * 'netdev' must be the network device that 'slave_' represents.  It is owned
+ * by the client, so the client must not close it before either unregistering
+ * 'slave_' or destroying 'bond'.
+ */
+void
+bond_slave_register(struct bond *bond, void *slave_, struct netdev *netdev)
+{
+    struct bond_slave *slave;
+
+    ovs_rwlock_wrlock(&rwlock);
+    slave = bond_slave_lookup(bond, slave_);
+    if (!slave) {
+        slave = xzalloc(sizeof *slave);
+
+        hmap_insert(&bond->slaves, &slave->hmap_node, hash_pointer(slave_, 0));
+        slave->bond = bond;
+        slave->aux = slave_;
+        slave->delay_expires = LLONG_MAX;
+        slave->name = xstrdup(netdev_get_name(netdev));
+        bond->bond_revalidate = true;
+
+        slave->enabled = false;
+        bond_enable_slave(slave, netdev_get_carrier(netdev));
+    }
+
+    bond_slave_set_netdev__(slave, netdev);
+
+    free(slave->name);
+    slave->name = xstrdup(netdev_get_name(netdev));
+    ovs_rwlock_unlock(&rwlock);
+}
+
+/* Updates the network device to be used with 'slave_' to 'netdev'.
+ *
+ * This is useful if the caller closes and re-opens the network device
+ * registered with bond_slave_register() but doesn't need to change anything
+ * else. */
+void
+bond_slave_set_netdev(struct bond *bond, void *slave_, struct netdev *netdev)
+{
+    struct bond_slave *slave;
+
+    ovs_rwlock_wrlock(&rwlock);
+    slave = bond_slave_lookup(bond, slave_);
+    if (slave) {
+        bond_slave_set_netdev__(slave, netdev);
+    }
+    ovs_rwlock_unlock(&rwlock);
+}
+
+/* Unregisters 'slave_' from 'bond'.  If 'bond' does not contain such a slave
+ * then this function has no effect.
+ *
+ * Unregistering a slave invalidates all flows. */
+void
+bond_slave_unregister(struct bond *bond, const void *slave_)
+{
+    struct bond_slave *slave;
+    bool del_active;
+
+    ovs_rwlock_wrlock(&rwlock);
+    slave = bond_slave_lookup(bond, slave_);
+    if (!slave) {
+        goto out;
+    }
+
+    bond->bond_revalidate = true;
+    bond_enable_slave(slave, false);
+
+    del_active = bond->active_slave == slave;
+    if (bond->hash) {
+        struct bond_entry *e;
+        for (e = bond->hash; e <= &bond->hash[BOND_MASK]; e++) {
+            if (e->slave == slave) {
+                e->slave = NULL;
+            }
+        }
+    }
+
+    free(slave->name);
+
+    hmap_remove(&bond->slaves, &slave->hmap_node);
+    /* Client owns 'slave->netdev'. */
+    free(slave);
+
+    if (del_active) {
+        bond_choose_active_slave(bond);
+        bond->send_learning_packets = true;
+    }
+out:
+    ovs_rwlock_unlock(&rwlock);
+}
+
+/* Should be called on each slave in 'bond' before bond_run() to indicate
+ * whether or not 'slave_' may be enabled. This function is intended to allow
+ * other protocols to have some impact on bonding decisions.  For example LACP
+ * or high level link monitoring protocols may decide that a given slave should
+ * not be able to send traffic. */
+void
+bond_slave_set_may_enable(struct bond *bond, void *slave_, bool may_enable)
+{
+    ovs_rwlock_wrlock(&rwlock);
+    bond_slave_lookup(bond, slave_)->may_enable = may_enable;
+    ovs_rwlock_unlock(&rwlock);
+}
+
+/* Performs periodic maintenance on 'bond'.
+ *
+ * Returns true if the caller should revalidate its flows.
+ *
+ * The caller should check bond_should_send_learning_packets() afterward. */
+bool
+bond_run(struct bond *bond, enum lacp_status lacp_status)
+{
+    struct bond_slave *slave;
+    bool revalidate;
+
+    ovs_rwlock_wrlock(&rwlock);
+    if (bond->lacp_status != lacp_status) {
+        bond->lacp_status = lacp_status;
+        bond->bond_revalidate = true;
+    }
+
+    /* Enable slaves based on link status and LACP feedback. */
+    HMAP_FOR_EACH (slave, hmap_node, &bond->slaves) {
+        bond_link_status_update(slave);
+        slave->change_seq = netdev_change_seq(slave->netdev);
+    }
+    if (!bond->active_slave || !bond->active_slave->enabled) {
+        bond_choose_active_slave(bond);
+    }
+
+    /* Update fake bond interface stats. */
+    if (time_msec() >= bond->next_fake_iface_update) {
+        bond_update_fake_slave_stats(bond);
+        bond->next_fake_iface_update = time_msec() + 1000;
+    }
+
+    revalidate = bond->bond_revalidate;
+    bond->bond_revalidate = false;
+    ovs_rwlock_unlock(&rwlock);
+
+    return revalidate;
+}
+
+/* Causes poll_block() to wake up when 'bond' needs something to be done. */
+void
+bond_wait(struct bond *bond)
+{
+    struct bond_slave *slave;
+
+    ovs_rwlock_rdlock(&rwlock);
+    HMAP_FOR_EACH (slave, hmap_node, &bond->slaves) {
+        if (slave->delay_expires != LLONG_MAX) {
+            poll_timer_wait_until(slave->delay_expires);
+        }
+
+        if (slave->change_seq != netdev_change_seq(slave->netdev)) {
+            poll_immediate_wake();
+        }
+    }
+
+    if (bond->next_fake_iface_update != LLONG_MAX) {
+        poll_timer_wait_until(bond->next_fake_iface_update);
+    }
+
+    if (bond->bond_revalidate) {
+        poll_immediate_wake();
+    }
+    ovs_rwlock_unlock(&rwlock);
+
+    /* We don't wait for bond->next_rebalance because rebalancing can only run
+     * at a flow account checkpoint.  ofproto does checkpointing on its own
+     * schedule and bond_rebalance() gets called afterward, so we'd just be
+     * waking up for no purpose. */
+}
+
+/* MAC learning table interaction. */
+
+static bool
+may_send_learning_packets(const struct bond *bond)
+{
+    return ((bond->lacp_status == LACP_DISABLED
+        && (bond->balance == BM_SLB || bond->balance == BM_AB))
+        || (bond->lacp_fallback_ab && bond->lacp_status == LACP_CONFIGURED))
+        && bond->active_slave;
+}
+
+/* Returns true if 'bond' needs the client to send out packets to assist with
+ * MAC learning on 'bond'.  If this function returns true, then the client
+ * should iterate through its MAC learning table for the bridge on which 'bond'
+ * is located.  For each MAC that has been learned on a port other than 'bond',
+ * it should call bond_compose_learning_packet().
+ *
+ * This function will only return true if 'bond' is in SLB or active-backup
+ * mode and LACP is not negotiated.  Otherwise sending learning packets isn't
+ * necessary.
+ *
+ * Calling this function resets the state that it checks. */
+bool
+bond_should_send_learning_packets(struct bond *bond)
+{
+    bool send;
+
+    ovs_rwlock_wrlock(&rwlock);
+    send = bond->send_learning_packets && may_send_learning_packets(bond);
+    bond->send_learning_packets = false;
+    ovs_rwlock_unlock(&rwlock);
+    return send;
+}
+
+/* Sends a gratuitous learning packet on 'bond' from 'eth_src' on 'vlan'.
+ *
+ * See bond_should_send_learning_packets() for description of usage. The
+ * caller should send the composed packet on the port associated with
+ * port_aux and takes ownership of the returned ofpbuf. */
+struct ofpbuf *
+bond_compose_learning_packet(struct bond *bond,
+                             const uint8_t eth_src[ETH_ADDR_LEN],
+                             uint16_t vlan, void **port_aux)
+{
+    struct bond_slave *slave;
+    struct ofpbuf *packet;
+    struct flow flow;
+
+    ovs_rwlock_rdlock(&rwlock);
+    ovs_assert(may_send_learning_packets(bond));
+    memset(&flow, 0, sizeof flow);
+    memcpy(flow.dl_src, eth_src, ETH_ADDR_LEN);
+    slave = choose_output_slave(bond, &flow, NULL, vlan);
+
+    packet = ofpbuf_new(0);
+    compose_rarp(packet, eth_src);
+    if (vlan) {
+        eth_push_vlan(packet, htons(vlan));
+    }
+
+    *port_aux = slave->aux;
+    ovs_rwlock_unlock(&rwlock);
+    return packet;
+}
+
+/* Checks whether a packet that arrived on 'slave_' within 'bond', with an
+ * Ethernet destination address of 'eth_dst', should be admitted.
+ *
+ * The return value is one of the following:
+ *
+ *    - BV_ACCEPT: Admit the packet.
+ *
+ *    - BV_DROP: Drop the packet.
+ *
+ *    - BV_DROP_IF_MOVED: Consult the MAC learning table for the packet's
+ *      Ethernet source address and VLAN.  If there is none, or if the packet
+ *      is on the learned port, then admit the packet.  If a different port has
+ *      been learned, however, drop the packet (and do not use it for MAC
+ *      learning).
+ */
+enum bond_verdict
+bond_check_admissibility(struct bond *bond, const void *slave_,
+                         const uint8_t eth_dst[ETH_ADDR_LEN])
+{
+    enum bond_verdict verdict = BV_DROP;
+    struct bond_slave *slave;
+
+    ovs_rwlock_rdlock(&rwlock);
+    slave = bond_slave_lookup(bond, slave_);
+    if (!slave) {
+        goto out;
+    }
+
+    /* LACP bonds have very loose admissibility restrictions because we can
+     * assume the remote switch is aware of the bond and will "do the right
+     * thing".  However, as a precaution we drop packets on disabled slaves
+     * because no correctly implemented partner switch should be sending
+     * packets to them.
+     *
+     * If LACP is configured, but LACP negotiations have been unsuccessful, we
+     * drop all incoming traffic except if lacp_fallback_ab is enabled. */
+    switch (bond->lacp_status) {
+    case LACP_NEGOTIATED:
+        verdict = slave->enabled ? BV_ACCEPT : BV_DROP;
+        goto out;
+    case LACP_CONFIGURED:
+        if (!bond->lacp_fallback_ab) {
+            goto out;
+        }
+    case LACP_DISABLED:
+        break;
+    }
+
+    /* Drop all multicast packets on inactive slaves. */
+    if (eth_addr_is_multicast(eth_dst)) {
+        if (bond->active_slave != slave) {
+            goto out;
+        }
+    }
+
+    switch (bond->balance) {
+    case BM_TCP:
+        /* TCP balanced bonds require successful LACP negotiations. Based on the
+         * above check, LACP is off or lacp_fallback_ab is true on this bond.
+         * If lacp_fallback_ab is true fall through to BM_AB case else, we
+         * drop all incoming traffic. */
+        if (!bond->lacp_fallback_ab) {
+            goto out;
+        }
+
+    case BM_AB:
+        /* Drop all packets which arrive on backup slaves.  This is similar to
+         * how Linux bonding handles active-backup bonds. */
+        if (bond->active_slave != slave) {
+            static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
+
+            VLOG_DBG_RL(&rl, "active-backup bond received packet on backup"
+                        " slave (%s) destined for " ETH_ADDR_FMT,
+                        slave->name, ETH_ADDR_ARGS(eth_dst));
+            goto out;
+        }
+        verdict = BV_ACCEPT;
+        goto out;
+
+    case BM_SLB:
+        /* Drop all packets for which we have learned a different input port,
+         * because we probably sent the packet on one slave and got it back on
+         * the other.  Gratuitous ARP packets are an exception to this rule:
+         * the host has moved to another switch.  The exception to the
+         * exception is if we locked the learning table to avoid reflections on
+         * bond slaves. */
+        verdict = BV_DROP_IF_MOVED;
+        goto out;
+    }
+
+    NOT_REACHED();
+out:
+    ovs_rwlock_unlock(&rwlock);
+    return verdict;
+
+}
+
+/* Returns the slave (registered on 'bond' by bond_slave_register()) to which
+ * a packet with the given 'flow' and 'vlan' should be forwarded.  Returns
+ * NULL if the packet should be dropped because no slaves are enabled.
+ *
+ * 'vlan' is not necessarily the same as 'flow->vlan_tci'.  First, 'vlan'
+ * should be a VID only (i.e. excluding the PCP bits).  Second,
+ * 'flow->vlan_tci' is the VLAN TCI that appeared on the packet (so it will be
+ * nonzero only for trunk ports), whereas 'vlan' is the logical VLAN that the
+ * packet belongs to (so for an access port it will be the access port's VLAN).
+ *
+ * If 'wc' is non-NULL, bitwise-OR's 'wc' with the set of bits that were
+ * significant in the selection.  At some point earlier, 'wc' should
+ * have been initialized (e.g., by flow_wildcards_init_catchall()).
+ */
+void *
+bond_choose_output_slave(struct bond *bond, const struct flow *flow,
+                         struct flow_wildcards *wc, uint16_t vlan)
+{
+    struct bond_slave *slave;
+    void *aux;
+
+    ovs_rwlock_rdlock(&rwlock);
+    slave = choose_output_slave(bond, flow, wc, vlan);
+    aux = slave ? slave->aux : NULL;
+    ovs_rwlock_unlock(&rwlock);
+
+    return aux;
+}
+
+/* Rebalancing. */
+
+static bool
+bond_is_balanced(const struct bond *bond) OVS_REQ_RDLOCK(rwlock)
+{
+    return bond->rebalance_interval
+        && (bond->balance == BM_SLB || bond->balance == BM_TCP);
+}
+
+/* Notifies 'bond' that 'n_bytes' bytes were sent in 'flow' within 'vlan'. */
+void
+bond_account(struct bond *bond, const struct flow *flow, uint16_t vlan,
+             uint64_t n_bytes)
+{
+    ovs_rwlock_wrlock(&rwlock);
+    if (bond_is_balanced(bond)) {
+        lookup_bond_entry(bond, flow, vlan)->tx_bytes += n_bytes;
+    }
+    ovs_rwlock_unlock(&rwlock);
+}
+
+static struct bond_slave *
+bond_slave_from_bal_node(struct list *bal) OVS_REQ_RDLOCK(rwlock)
+{
+    return CONTAINER_OF(bal, struct bond_slave, bal_node);
+}
+
+static void
+log_bals(struct bond *bond, const struct list *bals)
+{
+    if (VLOG_IS_DBG_ENABLED()) {
+        struct ds ds = DS_EMPTY_INITIALIZER;
+        const struct bond_slave *slave;
+
+        LIST_FOR_EACH (slave, bal_node, bals) {
+            if (ds.length) {
+                ds_put_char(&ds, ',');
+            }
+            ds_put_format(&ds, " %s %"PRIu64"kB",
+                          slave->name, slave->tx_bytes / 1024);
+
+            if (!slave->enabled) {
+                ds_put_cstr(&ds, " (disabled)");
+            }
+            if (!list_is_empty(&slave->entries)) {
+                struct bond_entry *e;
+
+                ds_put_cstr(&ds, " (");
+                LIST_FOR_EACH (e, list_node, &slave->entries) {
+                    if (&e->list_node != list_front(&slave->entries)) {
+                        ds_put_cstr(&ds, " + ");
+                    }
+                    ds_put_format(&ds, "h%"PRIdPTR": %"PRIu64"kB",
+                                  e - bond->hash, e->tx_bytes / 1024);
+                }
+                ds_put_cstr(&ds, ")");
+            }
+        }
+        VLOG_DBG("bond %s:%s", bond->name, ds_cstr(&ds));
+        ds_destroy(&ds);
+    }
+}
+
+/* Shifts 'hash' from its current slave to 'to'. */
+static void
+bond_shift_load(struct bond_entry *hash, struct bond_slave *to)
+{
+    struct bond_slave *from = hash->slave;
+    struct bond *bond = from->bond;
+    uint64_t delta = hash->tx_bytes;
+
+    VLOG_INFO("bond %s: shift %"PRIu64"kB of load (with hash %"PRIdPTR") "
+              "from %s to %s (now carrying %"PRIu64"kB and "
+              "%"PRIu64"kB load, respectively)",
+              bond->name, delta / 1024, hash - bond->hash,
+              from->name, to->name,
+              (from->tx_bytes - delta) / 1024,
+              (to->tx_bytes + delta) / 1024);
+
+    /* Shift load away from 'from' to 'to'. */
+    from->tx_bytes -= delta;
+    to->tx_bytes += delta;
+
+    /* Arrange for flows to be revalidated. */
+    hash->slave = to;
+    bond->bond_revalidate = true;
+}
+
+/* Picks and returns a bond_entry to migrate from 'from' (the most heavily
+ * loaded bond slave) to a bond slave that has 'to_tx_bytes' bytes of load,
+ * given that doing so must decrease the ratio of the load on the two slaves by
+ * at least 0.1.  Returns NULL if there is no appropriate entry.
+ *
+ * The list of entries isn't sorted.  I don't know of a reason to prefer to
+ * shift away small hashes or large hashes. */
+static struct bond_entry *
+choose_entry_to_migrate(const struct bond_slave *from, uint64_t to_tx_bytes)
+{
+    struct bond_entry *e;
+
+    if (list_is_short(&from->entries)) {
+        /* 'from' carries no more than one MAC hash, so shifting load away from
+         * it would be pointless. */
+        return NULL;
+    }
+
+    LIST_FOR_EACH (e, list_node, &from->entries) {
+        double old_ratio, new_ratio;
+        uint64_t delta;
+
+        if (to_tx_bytes == 0) {
+            /* Nothing on the new slave, move it. */
+            return e;
+        }
+
+        delta = e->tx_bytes;
+        old_ratio = (double)from->tx_bytes / to_tx_bytes;
+        new_ratio = (double)(from->tx_bytes - delta) / (to_tx_bytes + delta);
+        if (old_ratio - new_ratio > 0.1
+            && fabs(new_ratio - 1.0) < fabs(old_ratio - 1.0)) {
+            /* We're aiming for an ideal ratio of 1, meaning both the 'from'
+               and 'to' slave have the same load.  Therefore, we only move an
+               entry if it decreases the load on 'from', and brings us closer
+               to equal traffic load. */
+            return e;
+        }
+    }
+
+    return NULL;
+}
+
+/* Inserts 'slave' into 'bals' so that descending order of 'tx_bytes' is
+ * maintained. */
+static void
+insert_bal(struct list *bals, struct bond_slave *slave)
+{
+    struct bond_slave *pos;
+
+    LIST_FOR_EACH (pos, bal_node, bals) {
+        if (slave->tx_bytes > pos->tx_bytes) {
+            break;
+        }
+    }
+    list_insert(&pos->bal_node, &slave->bal_node);
+}
+
+/* Removes 'slave' from its current list and then inserts it into 'bals' so
+ * that descending order of 'tx_bytes' is maintained. */
+static void
+reinsert_bal(struct list *bals, struct bond_slave *slave)
+{
+    list_remove(&slave->bal_node);
+    insert_bal(bals, slave);
+}
+
+/* If 'bond' needs rebalancing, does so.
+ *
+ * The caller should have called bond_account() for each active flow, to ensure
+ * that flow data is consistently accounted at this point. */
+void
+bond_rebalance(struct bond *bond)
+{
+    struct bond_slave *slave;
+    struct bond_entry *e;
+    struct list bals;
+
+    ovs_rwlock_wrlock(&rwlock);
+    if (!bond_is_balanced(bond) || time_msec() < bond->next_rebalance) {
+        ovs_rwlock_unlock(&rwlock);
+        return;
+    }
+    bond->next_rebalance = time_msec() + bond->rebalance_interval;
+
+    /* Add each bond_entry to its slave's 'entries' list.
+     * Compute each slave's tx_bytes as the sum of its entries' tx_bytes. */
+    HMAP_FOR_EACH (slave, hmap_node, &bond->slaves) {
+        slave->tx_bytes = 0;
+        list_init(&slave->entries);
+    }
+    for (e = &bond->hash[0]; e <= &bond->hash[BOND_MASK]; e++) {
+        if (e->slave && e->tx_bytes) {
+            e->slave->tx_bytes += e->tx_bytes;
+            list_push_back(&e->slave->entries, &e->list_node);
+        }
+    }
+
+    /* Add enabled slaves to 'bals' in descending order of tx_bytes.
+     *
+     * XXX This is O(n**2) in the number of slaves but it could be O(n lg n)
+     * with a proper list sort algorithm. */
+    list_init(&bals);
+    HMAP_FOR_EACH (slave, hmap_node, &bond->slaves) {
+        if (slave->enabled) {
+            insert_bal(&bals, slave);
+        }
+    }
+    log_bals(bond, &bals);
+
+    /* Shift load from the most-loaded slaves to the least-loaded slaves. */
+    while (!list_is_short(&bals)) {
+        struct bond_slave *from = bond_slave_from_bal_node(list_front(&bals));
+        struct bond_slave *to = bond_slave_from_bal_node(list_back(&bals));
+        uint64_t overload;
+
+        overload = from->tx_bytes - to->tx_bytes;
+        if (overload < to->tx_bytes >> 5 || overload < 100000) {
+            /* The extra load on 'from' (and all less-loaded slaves), compared
+             * to that of 'to' (the least-loaded slave), is less than ~3%, or
+             * it is less than ~1Mbps.  No point in rebalancing. */
+            break;
+        }
+
+        /* 'from' is carrying significantly more load than 'to'.  Pick a hash
+         * to move from 'from' to 'to'. */
+        e = choose_entry_to_migrate(from, to->tx_bytes);
+        if (e) {
+            bond_shift_load(e, to);
+
+            /* Delete element from from->entries.
+             *
+             * We don't add the element to to->hashes.  That would only allow
+             * 'e' to be migrated to another slave in this rebalancing run, and
+             * there is no point in doing that. */
+            list_remove(&e->list_node);
+
+            /* Re-sort 'bals'. */
+            reinsert_bal(&bals, from);
+            reinsert_bal(&bals, to);
+        } else {
+            /* Can't usefully migrate anything away from 'from'.
+             * Don't reconsider it. */
+            list_remove(&from->bal_node);
+        }
+    }
+
+    /* Implement exponentially weighted moving average.  A weight of 1/2 causes
+     * historical data to decay to <1% in 7 rebalancing runs.  1,000,000 bytes
+     * take 20 rebalancing runs to decay to 0 and get deleted entirely. */
+    for (e = &bond->hash[0]; e <= &bond->hash[BOND_MASK]; e++) {
+        e->tx_bytes /= 2;
+        if (!e->tx_bytes) {
+            e->slave = NULL;
+        }
+    }
+    ovs_rwlock_unlock(&rwlock);
+}
+
+/* Bonding unixctl user interface functions. */
+
+static struct bond *
+bond_find(const char *name) OVS_REQ_RDLOCK(rwlock)
+{
+    struct bond *bond;
+
+    HMAP_FOR_EACH_WITH_HASH (bond, hmap_node, hash_string(name, 0),
+                             all_bonds) {
+        if (!strcmp(bond->name, name)) {
+            return bond;
+        }
+    }
+    return NULL;
+}
+
+static struct bond_slave *
+bond_lookup_slave(struct bond *bond, const char *slave_name)
+{
+    struct bond_slave *slave;
+
+    HMAP_FOR_EACH (slave, hmap_node, &bond->slaves) {
+        if (!strcmp(slave->name, slave_name)) {
+            return slave;
+        }
+    }
+    return NULL;
+}
+
+static void
+bond_unixctl_list(struct unixctl_conn *conn,
+                  int argc OVS_UNUSED, const char *argv[] OVS_UNUSED,
+                  void *aux OVS_UNUSED)
+{
+    struct ds ds = DS_EMPTY_INITIALIZER;
+    const struct bond *bond;
+
+    ds_put_cstr(&ds, "bond\ttype\tslaves\n");
+
+    ovs_rwlock_rdlock(&rwlock);
+    HMAP_FOR_EACH (bond, hmap_node, all_bonds) {
+        const struct bond_slave *slave;
+        size_t i;
+
+        ds_put_format(&ds, "%s\t%s\t",
+                      bond->name, bond_mode_to_string(bond->balance));
+
+        i = 0;
+        HMAP_FOR_EACH (slave, hmap_node, &bond->slaves) {
+            if (i++ > 0) {
+                ds_put_cstr(&ds, ", ");
+            }
+            ds_put_cstr(&ds, slave->name);
+        }
+        ds_put_char(&ds, '\n');
+    }
+    ovs_rwlock_unlock(&rwlock);
+    unixctl_command_reply(conn, ds_cstr(&ds));
+    ds_destroy(&ds);
+}
+
+static void
+bond_print_details(struct ds *ds, const struct bond *bond)
+    OVS_REQ_RDLOCK(rwlock)
+{
+    struct shash slave_shash = SHASH_INITIALIZER(&slave_shash);
+    const struct shash_node **sorted_slaves = NULL;
+    const struct bond_slave *slave;
+    int i;
+
+    ds_put_format(ds, "---- %s ----\n", bond->name);
+    ds_put_format(ds, "bond_mode: %s\n",
+                  bond_mode_to_string(bond->balance));
+
+    ds_put_format(ds, "bond-hash-basis: %"PRIu32"\n", bond->basis);
+
+    ds_put_format(ds, "updelay: %d ms\n", bond->updelay);
+    ds_put_format(ds, "downdelay: %d ms\n", bond->downdelay);
+
+    if (bond_is_balanced(bond)) {
+        ds_put_format(ds, "next rebalance: %lld ms\n",
+                      bond->next_rebalance - time_msec());
+    }
+
+    ds_put_cstr(ds, "lacp_status: ");
+    switch (bond->lacp_status) {
+    case LACP_NEGOTIATED:
+        ds_put_cstr(ds, "negotiated\n");
+        break;
+    case LACP_CONFIGURED:
+        ds_put_cstr(ds, "configured\n");
+        break;
+    case LACP_DISABLED:
+        ds_put_cstr(ds, "off\n");
+        break;
+    default:
+        ds_put_cstr(ds, "<unknown>\n");
+        break;
+    }
+
+    HMAP_FOR_EACH (slave, hmap_node, &bond->slaves) {
+        shash_add(&slave_shash, slave->name, slave);
+    }
+    sorted_slaves = shash_sort(&slave_shash);
+
+    for (i = 0; i < shash_count(&slave_shash); i++) {
+        struct bond_entry *be;
+
+        slave = sorted_slaves[i]->data;
+
+        /* Basic info. */
+        ds_put_format(ds, "\nslave %s: %s\n",
+                      slave->name, slave->enabled ? "enabled" : "disabled");
+        if (slave == bond->active_slave) {
+            ds_put_cstr(ds, "\tactive slave\n");
+        }
+        if (slave->delay_expires != LLONG_MAX) {
+            ds_put_format(ds, "\t%s expires in %lld ms\n",
+                          slave->enabled ? "downdelay" : "updelay",
+                          slave->delay_expires - time_msec());
+        }
+
+        ds_put_format(ds, "\tmay_enable: %s\n",
+                      slave->may_enable ? "true" : "false");
+
+        if (!bond_is_balanced(bond)) {
+            continue;
+        }
+
+        /* Hashes. */
+        for (be = bond->hash; be <= &bond->hash[BOND_MASK]; be++) {
+            int hash = be - bond->hash;
+
+            if (be->slave != slave) {
+                continue;
+            }
+
+            ds_put_format(ds, "\thash %d: %"PRIu64" kB load\n",
+                          hash, be->tx_bytes / 1024);
+
+            /* XXX How can we list the MACs assigned to hashes of SLB bonds? */
+        }
+    }
+    shash_destroy(&slave_shash);
+    free(sorted_slaves);
+    ds_put_cstr(ds, "\n");
+}
+
+static void
+bond_unixctl_show(struct unixctl_conn *conn,
+                  int argc, const char *argv[],
+                  void *aux OVS_UNUSED)
+{
+    struct ds ds = DS_EMPTY_INITIALIZER;
+
+    ovs_rwlock_rdlock(&rwlock);
+    if (argc > 1) {
+        const struct bond *bond = bond_find(argv[1]);
+
+        if (!bond) {
+            unixctl_command_reply_error(conn, "no such bond");
+            goto out;
+        }
+        bond_print_details(&ds, bond);
+    } else {
+        const struct bond *bond;
+
+        HMAP_FOR_EACH (bond, hmap_node, all_bonds) {
+            bond_print_details(&ds, bond);
+        }
+    }
+
+    unixctl_command_reply(conn, ds_cstr(&ds));
+    ds_destroy(&ds);
+
+out:
+    ovs_rwlock_unlock(&rwlock);
+}
+
+static void
+bond_unixctl_migrate(struct unixctl_conn *conn,
+                     int argc OVS_UNUSED, const char *argv[],
+                     void *aux OVS_UNUSED)
+{
+    const char *bond_s = argv[1];
+    const char *hash_s = argv[2];
+    const char *slave_s = argv[3];
+    struct bond *bond;
+    struct bond_slave *slave;
+    struct bond_entry *entry;
+    int hash;
+
+    ovs_rwlock_wrlock(&rwlock);
+    bond = bond_find(bond_s);
+    if (!bond) {
+        unixctl_command_reply_error(conn, "no such bond");
+        goto out;
+    }
+
+    if (bond->balance != BM_SLB) {
+        unixctl_command_reply_error(conn, "not an SLB bond");
+        goto out;
+    }
+
+    if (strspn(hash_s, "0123456789") == strlen(hash_s)) {
+        hash = atoi(hash_s) & BOND_MASK;
+    } else {
+        unixctl_command_reply_error(conn, "bad hash");
+        goto out;
+    }
+
+    slave = bond_lookup_slave(bond, slave_s);
+    if (!slave) {
+        unixctl_command_reply_error(conn, "no such slave");
+        goto out;
+    }
+
+    if (!slave->enabled) {
+        unixctl_command_reply_error(conn, "cannot migrate to disabled slave");
+        goto out;
+    }
+
+    entry = &bond->hash[hash];
+    bond->bond_revalidate = true;
+    entry->slave = slave;
+    unixctl_command_reply(conn, "migrated");
+
+out:
+    ovs_rwlock_unlock(&rwlock);
+}
+
+static void
+bond_unixctl_set_active_slave(struct unixctl_conn *conn,
+                              int argc OVS_UNUSED, const char *argv[],
+                              void *aux OVS_UNUSED)
+{
+    const char *bond_s = argv[1];
+    const char *slave_s = argv[2];
+    struct bond *bond;
+    struct bond_slave *slave;
+
+    ovs_rwlock_wrlock(&rwlock);
+    bond = bond_find(bond_s);
+    if (!bond) {
+        unixctl_command_reply_error(conn, "no such bond");
+        goto out;
+    }
+
+    slave = bond_lookup_slave(bond, slave_s);
+    if (!slave) {
+        unixctl_command_reply_error(conn, "no such slave");
+        goto out;
+    }
+
+    if (!slave->enabled) {
+        unixctl_command_reply_error(conn, "cannot make disabled slave active");
+        goto out;
+    }
+
+    if (bond->active_slave != slave) {
+        bond->bond_revalidate = true;
+        bond->active_slave = slave;
+        VLOG_INFO("bond %s: active interface is now %s",
+                  bond->name, slave->name);
+        bond->send_learning_packets = true;
+        unixctl_command_reply(conn, "done");
+    } else {
+        unixctl_command_reply(conn, "no change");
+    }
+out:
+    ovs_rwlock_unlock(&rwlock);
+}
+
+static void
+enable_slave(struct unixctl_conn *conn, const char *argv[], bool enable)
+{
+    const char *bond_s = argv[1];
+    const char *slave_s = argv[2];
+    struct bond *bond;
+    struct bond_slave *slave;
+
+    ovs_rwlock_wrlock(&rwlock);
+    bond = bond_find(bond_s);
+    if (!bond) {
+        unixctl_command_reply_error(conn, "no such bond");
+        goto out;
+    }
+
+    slave = bond_lookup_slave(bond, slave_s);
+    if (!slave) {
+        unixctl_command_reply_error(conn, "no such slave");
+        goto out;
+    }
+
+    bond_enable_slave(slave, enable);
+    unixctl_command_reply(conn, enable ? "enabled" : "disabled");
+
+out:
+    ovs_rwlock_unlock(&rwlock);
+}
+
+static void
+bond_unixctl_enable_slave(struct unixctl_conn *conn,
+                          int argc OVS_UNUSED, const char *argv[],
+                          void *aux OVS_UNUSED)
+{
+    enable_slave(conn, argv, true);
+}
+
+static void
+bond_unixctl_disable_slave(struct unixctl_conn *conn,
+                           int argc OVS_UNUSED, const char *argv[],
+                           void *aux OVS_UNUSED)
+{
+    enable_slave(conn, argv, false);
+}
+
+static void
+bond_unixctl_hash(struct unixctl_conn *conn, int argc, const char *argv[],
+                  void *aux OVS_UNUSED)
+{
+    const char *mac_s = argv[1];
+    const char *vlan_s = argc > 2 ? argv[2] : NULL;
+    const char *basis_s = argc > 3 ? argv[3] : NULL;
+    uint8_t mac[ETH_ADDR_LEN];
+    uint8_t hash;
+    char *hash_cstr;
+    unsigned int vlan;
+    uint32_t basis;
+
+    if (vlan_s) {
+        if (!ovs_scan(vlan_s, "%u", &vlan)) {
+            unixctl_command_reply_error(conn, "invalid vlan");
+            return;
+        }
+    } else {
+        vlan = 0;
+    }
+
+    if (basis_s) {
+        if (!ovs_scan(basis_s, "%"SCNu32, &basis)) {
+            unixctl_command_reply_error(conn, "invalid basis");
+            return;
+        }
+    } else {
+        basis = 0;
+    }
+
+    if (ovs_scan(mac_s, ETH_ADDR_SCAN_FMT, ETH_ADDR_SCAN_ARGS(mac))) {
+        hash = bond_hash_src(mac, vlan, basis) & BOND_MASK;
+
+        hash_cstr = xasprintf("%u", hash);
+        unixctl_command_reply(conn, hash_cstr);
+        free(hash_cstr);
+    } else {
+        unixctl_command_reply_error(conn, "invalid mac");
+    }
+}
+
+void
+bond_init(void)
+{
+    unixctl_command_register("bond/list", "", 0, 0, bond_unixctl_list, NULL);
+    unixctl_command_register("bond/show", "[port]", 0, 1, bond_unixctl_show,
+                             NULL);
+    unixctl_command_register("bond/migrate", "port hash slave", 3, 3,
+                             bond_unixctl_migrate, NULL);
+    unixctl_command_register("bond/set-active-slave", "port slave", 2, 2,
+                             bond_unixctl_set_active_slave, NULL);
+    unixctl_command_register("bond/enable-slave", "port slave", 2, 2,
+                             bond_unixctl_enable_slave, NULL);
+    unixctl_command_register("bond/disable-slave", "port slave", 2, 2,
+                             bond_unixctl_disable_slave, NULL);
+    unixctl_command_register("bond/hash", "mac [vlan] [basis]", 1, 3,
+                             bond_unixctl_hash, NULL);
+}
+
+static void
+bond_entry_reset(struct bond *bond)
+{
+    if (bond->balance != BM_AB) {
+        size_t hash_len = (BOND_MASK + 1) * sizeof *bond->hash;
+
+        if (!bond->hash) {
+            bond->hash = xmalloc(hash_len);
+        }
+        memset(bond->hash, 0, hash_len);
+
+        bond->next_rebalance = time_msec() + bond->rebalance_interval;
+    } else {
+        free(bond->hash);
+        bond->hash = NULL;
+    }
+}
+
+static struct bond_slave *
+bond_slave_lookup(struct bond *bond, const void *slave_)
+{
+    struct bond_slave *slave;
+
+    HMAP_FOR_EACH_IN_BUCKET (slave, hmap_node, hash_pointer(slave_, 0),
+                             &bond->slaves) {
+        if (slave->aux == slave_) {
+            return slave;
+        }
+    }
+
+    return NULL;
+}
+
+static void
+bond_enable_slave(struct bond_slave *slave, bool enable)
+{
+    slave->delay_expires = LLONG_MAX;
+    if (enable != slave->enabled) {
+        slave->bond->bond_revalidate = true;
+        slave->enabled = enable;
+        VLOG_INFO("interface %s: %s", slave->name,
+                  slave->enabled ? "enabled" : "disabled");
+    }
+}
+
+static void
+bond_link_status_update(struct bond_slave *slave)
+{
+    struct bond *bond = slave->bond;
+    bool up;
+
+    up = netdev_get_carrier(slave->netdev) && slave->may_enable;
+    if ((up == slave->enabled) != (slave->delay_expires == LLONG_MAX)) {
+        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 20);
+        VLOG_INFO_RL(&rl, "interface %s: link state %s",
+                     slave->name, up ? "up" : "down");
+        if (up == slave->enabled) {
+            slave->delay_expires = LLONG_MAX;
+            VLOG_INFO_RL(&rl, "interface %s: will not be %s",
+                         slave->name, up ? "disabled" : "enabled");
+        } else {
+            int delay = (bond->lacp_status != LACP_DISABLED ? 0
+                         : up ? bond->updelay : bond->downdelay);
+            slave->delay_expires = time_msec() + delay;
+            if (delay) {
+                VLOG_INFO_RL(&rl, "interface %s: will be %s if it stays %s "
+                             "for %d ms",
+                             slave->name,
+                             up ? "enabled" : "disabled",
+                             up ? "up" : "down",
+                             delay);
+            }
+        }
+    }
+
+    if (time_msec() >= slave->delay_expires) {
+        bond_enable_slave(slave, up);
+    }
+}
+
+static unsigned int
+bond_hash_src(const uint8_t mac[ETH_ADDR_LEN], uint16_t vlan, uint32_t basis)
+{
+    return hash_3words(hash_bytes(mac, ETH_ADDR_LEN, 0), vlan, basis);
+}
+
+static unsigned int
+bond_hash_tcp(const struct flow *flow, uint16_t vlan, uint32_t basis)
+{
+    struct flow hash_flow = *flow;
+    hash_flow.vlan_tci = htons(vlan);
+
+    /* The symmetric quality of this hash function is not required, but
+     * flow_hash_symmetric_l4 already exists, and is sufficient for our
+     * purposes, so we use it out of convenience. */
+    return flow_hash_symmetric_l4(&hash_flow, basis);
+}
+
+static unsigned int
+bond_hash(const struct bond *bond, const struct flow *flow, uint16_t vlan)
+{
+    ovs_assert(bond->balance == BM_TCP || bond->balance == BM_SLB);
+
+    return (bond->balance == BM_TCP
+            ? bond_hash_tcp(flow, vlan, bond->basis)
+            : bond_hash_src(flow->dl_src, vlan, bond->basis));
+}
+
+static struct bond_entry *
+lookup_bond_entry(const struct bond *bond, const struct flow *flow,
+                  uint16_t vlan)
+{
+    return &bond->hash[bond_hash(bond, flow, vlan) & BOND_MASK];
+}
+
+static struct bond_slave *
+choose_output_slave(const struct bond *bond, const struct flow *flow,
+                    struct flow_wildcards *wc, uint16_t vlan)
+{
+    struct bond_entry *e;
+    int balance;
+
+    balance = bond->balance;
+    if (bond->lacp_status == LACP_CONFIGURED) {
+        /* LACP has been configured on this bond but negotiations were
+         * unsuccussful. If lacp_fallback_ab is enabled use active-
+         * backup mode else drop all traffic. */
+        if (!bond->lacp_fallback_ab) {
+            return NULL;
+        }
+        balance = BM_AB;
+    }
+
+    switch (balance) {
+    case BM_AB:
+        return bond->active_slave;
+
+    case BM_TCP:
+        if (bond->lacp_status != LACP_NEGOTIATED) {
+            /* Must have LACP negotiations for TCP balanced bonds. */
+            return NULL;
+        }
+        if (wc) {
+            flow_mask_hash_fields(flow, wc, NX_HASH_FIELDS_SYMMETRIC_L4);
+        }
+        /* Fall Through. */
+    case BM_SLB:
+        if (wc) {
+            flow_mask_hash_fields(flow, wc, NX_HASH_FIELDS_ETH_SRC);
+        }
+        e = lookup_bond_entry(bond, flow, vlan);
+        if (!e->slave || !e->slave->enabled) {
+            e->slave = CONTAINER_OF(hmap_random_node(&bond->slaves),
+                                    struct bond_slave, hmap_node);
+            if (!e->slave->enabled) {
+                e->slave = bond->active_slave;
+            }
+        }
+        return e->slave;
+
+    default:
+        NOT_REACHED();
+    }
+}
+
+static struct bond_slave *
+bond_choose_slave(const struct bond *bond)
+{
+    struct bond_slave *slave, *best;
+
+    /* Find an enabled slave. */
+    HMAP_FOR_EACH (slave, hmap_node, &bond->slaves) {
+        if (slave->enabled) {
+            return slave;
+        }
+    }
+
+    /* All interfaces are disabled.  Find an interface that will be enabled
+     * after its updelay expires.  */
+    best = NULL;
+    HMAP_FOR_EACH (slave, hmap_node, &bond->slaves) {
+        if (slave->delay_expires != LLONG_MAX
+            && slave->may_enable
+            && (!best || slave->delay_expires < best->delay_expires)) {
+            best = slave;
+        }
+    }
+    return best;
+}
+
+static void
+bond_choose_active_slave(struct bond *bond)
+{
+    static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 20);
+    struct bond_slave *old_active_slave = bond->active_slave;
+
+    bond->active_slave = bond_choose_slave(bond);
+    if (bond->active_slave) {
+        if (bond->active_slave->enabled) {
+            VLOG_INFO_RL(&rl, "bond %s: active interface is now %s",
+                         bond->name, bond->active_slave->name);
+        } else {
+            VLOG_INFO_RL(&rl, "bond %s: active interface is now %s, skipping "
+                         "remaining %lld ms updelay (since no interface was "
+                         "enabled)", bond->name, bond->active_slave->name,
+                         bond->active_slave->delay_expires - time_msec());
+            bond_enable_slave(bond->active_slave, true);
+        }
+
+        bond->send_learning_packets = true;
+    } else if (old_active_slave) {
+        VLOG_INFO_RL(&rl, "bond %s: all interfaces disabled", bond->name);
+    }
+}
+
+/* Attempts to make the sum of the bond slaves' statistics appear on the fake
+ * bond interface. */
+static void
+bond_update_fake_slave_stats(struct bond *bond)
+{
+    struct netdev_stats bond_stats;
+    struct bond_slave *slave;
+    struct netdev *bond_dev;
+
+    memset(&bond_stats, 0, sizeof bond_stats);
+
+    HMAP_FOR_EACH (slave, hmap_node, &bond->slaves) {
+        struct netdev_stats slave_stats;
+
+        if (!netdev_get_stats(slave->netdev, &slave_stats)) {
+            /* XXX: We swap the stats here because they are swapped back when
+             * reported by the internal device.  The reason for this is
+             * internal devices normally represent packets going into the
+             * system but when used as fake bond device they represent packets
+             * leaving the system.  We really should do this in the internal
+             * device itself because changing it here reverses the counts from
+             * the perspective of the switch.  However, the internal device
+             * doesn't know what type of device it represents so we have to do
+             * it here for now. */
+            bond_stats.tx_packets += slave_stats.rx_packets;
+            bond_stats.tx_bytes += slave_stats.rx_bytes;
+            bond_stats.rx_packets += slave_stats.tx_packets;
+            bond_stats.rx_bytes += slave_stats.tx_bytes;
+        }
+    }
+
+    if (!netdev_open(bond->name, "system", &bond_dev)) {
+        netdev_set_stats(bond_dev, &bond_stats);
+        netdev_close(bond_dev);
+    }
+}