/*
 * Copyright (c) 2007-2014 Nicira, Inc.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA
 */

#include "flow.h"
#include "datapath.h"
#include "flow_netlink.h"
#include <linux/uaccess.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/if_ether.h>
#include <linux/if_vlan.h>
#include <net/llc_pdu.h>
#include <linux/kernel.h>
#include <linux/jhash.h>
#include <linux/jiffies.h>
#include <linux/llc.h>
#include <linux/module.h>
#include <linux/in.h>
#include <linux/rcupdate.h>
#include <linux/cpumask.h>
#include <linux/if_arp.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/sctp.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/icmp.h>
#include <linux/icmpv6.h>
#include <linux/rculist.h>
#include <linux/sort.h>
#include <net/ip.h>
#include <net/ipv6.h>
#include <net/ndisc.h>

#define TBL_MIN_BUCKETS         1024
#define MASK_ARRAY_SIZE_MIN     16
#define REHASH_INTERVAL         (10 * 60 * HZ)

#define MC_DEFAULT_HASH_ENTRIES 256
#define MC_HASH_SHIFT           8
#define MC_HASH_SEGS            ((sizeof(uint32_t) * 8) / MC_HASH_SHIFT)

static struct kmem_cache *flow_cache;
struct kmem_cache *flow_stats_cache __read_mostly;

static u16 range_n_bytes(const struct sw_flow_key_range *range)
{
        return range->end - range->start;
}

void ovs_flow_mask_key(struct sw_flow_key *dst, const struct sw_flow_key *src,
                       bool full, const struct sw_flow_mask *mask)
{
        int start = full ? 0 : mask->range.start;
        int len = full ? sizeof *dst : range_n_bytes(&mask->range);
        const long *m = (const long *)((const u8 *)&mask->key + start);
        const long *s = (const long *)((const u8 *)src + start);
        long *d = (long *)((u8 *)dst + start);
        int i;

        /* If 'full' is true then all of 'dst' is fully initialized. Otherwise,
         * if 'full' is false the memory outside of the 'mask->range' is left
         * uninitialized. This can be used as an optimization when further
         * operations on 'dst' only use contents within 'mask->range'.
         */
        for (i = 0; i < len; i += sizeof(long))
                *d++ = *s++ & *m++;
}

struct sw_flow *ovs_flow_alloc(void)
{
        struct sw_flow *flow;
        struct sw_flow_stats *stats;

        flow = kmem_cache_zalloc(flow_cache, GFP_KERNEL);
        if (!flow)
                return ERR_PTR(-ENOMEM);

        flow->stats_last_writer = -1;

        /* Initialize the default stat node. */
        stats = kmem_cache_alloc_node(flow_stats_cache,
                                      GFP_KERNEL | __GFP_ZERO,
                                      node_online(0) ? 0 : NUMA_NO_NODE);
        if (!stats)
                goto err;

        spin_lock_init(&stats->lock);

        RCU_INIT_POINTER(flow->stats[0], stats);

        cpumask_set_cpu(0, &flow->cpu_used_mask);

        return flow;
err:
        kmem_cache_free(flow_cache, flow);
        return ERR_PTR(-ENOMEM);
}

int ovs_flow_tbl_count(const struct flow_table *table)
{
        return table->count;
}

static void flow_free(struct sw_flow *flow)
{
        int cpu;

        if (ovs_identifier_is_key(&flow->id))
                kfree(flow->id.unmasked_key);
        if (flow->sf_acts)
                ovs_nla_free_flow_actions((struct sw_flow_actions __force *)
                                          flow->sf_acts);
        /* We open code this to make sure cpu 0 is always considered */
        for (cpu = 0; cpu < nr_cpu_ids;
             cpu = cpumask_next(cpu, &flow->cpu_used_mask)) {
                if (flow->stats[cpu])
                        kmem_cache_free(flow_stats_cache,
                                        (struct sw_flow_stats __force *)flow->stats[cpu]);
        }

        kmem_cache_free(flow_cache, flow);
}

static void rcu_free_flow_callback(struct rcu_head *rcu)
{
        struct sw_flow *flow = container_of(rcu, struct sw_flow, rcu);

        flow_free(flow);
}

void ovs_flow_free(struct sw_flow *flow, bool deferred)
{
        if (!flow)
                return;

        if (deferred)
                call_rcu(&flow->rcu, rcu_free_flow_callback);
        else
                flow_free(flow);
}

static void __table_instance_destroy(struct table_instance *ti)
{
        kvfree(ti->buckets);
        kfree(ti);
}

static struct table_instance *table_instance_alloc(int new_size)
{
        struct table_instance *ti = kmalloc(sizeof(*ti), GFP_KERNEL);
        int i;

        if (!ti)
                return NULL;

        ti->buckets = kvmalloc_array(new_size, sizeof(struct hlist_head),
                                     GFP_KERNEL);
        if (!ti->buckets) {
                kfree(ti);
                return NULL;
        }

        for (i = 0; i < new_size; i++)
                INIT_HLIST_HEAD(&ti->buckets[i]);

        ti->n_buckets = new_size;
        ti->node_ver = 0;
        get_random_bytes(&ti->hash_seed, sizeof(u32));

        return ti;
}

static void __mask_array_destroy(struct mask_array *ma)
{
        free_percpu(ma->masks_usage_stats);
        kfree(ma);
}

static void mask_array_rcu_cb(struct rcu_head *rcu)
{
        struct mask_array *ma = container_of(rcu, struct mask_array, rcu);

        __mask_array_destroy(ma);
}

static void tbl_mask_array_reset_counters(struct mask_array *ma)
{
        int i, cpu;

        /* As the per CPU counters are not atomic we can not go ahead and
         * reset them from another CPU. To be able to still have an approximate
         * zero based counter we store the value at reset, and subtract it
         * later when processing.
         */
        for (i = 0; i < ma->max; i++) {
                ma->masks_usage_zero_cntr[i] = 0;

                for_each_possible_cpu(cpu) {
                        struct mask_array_stats *stats;
                        unsigned int start;
                        u64 counter;

                        stats = per_cpu_ptr(ma->masks_usage_stats, cpu);
                        do {
                                start = u64_stats_fetch_begin_irq(&stats->syncp);
                                counter = stats->usage_cntrs[i];
                        } while (u64_stats_fetch_retry_irq(&stats->syncp, start));

                        ma->masks_usage_zero_cntr[i] += counter;
                }
        }
}

static struct mask_array *tbl_mask_array_alloc(int size)
{
        struct mask_array *new;

        size = max(MASK_ARRAY_SIZE_MIN, size);
        new = kzalloc(sizeof(struct mask_array) +
                      sizeof(struct sw_flow_mask *) * size +
                      sizeof(u64) * size, GFP_KERNEL);
        if (!new)
                return NULL;

        new->masks_usage_zero_cntr = (u64 *)((u8 *)new +
                                             sizeof(struct mask_array) +
                                             sizeof(struct sw_flow_mask *) *
                                             size);

        new->masks_usage_stats = __alloc_percpu(sizeof(struct mask_array_stats) +
                                                sizeof(u64) * size,
                                                __alignof__(u64));
        if (!new->masks_usage_stats) {
                kfree(new);
                return NULL;
        }

        new->count = 0;
        new->max = size;

        return new;
}

static int tbl_mask_array_realloc(struct flow_table *tbl, int size)
{
        struct mask_array *old;
        struct mask_array *new;

        new = tbl_mask_array_alloc(size);
        if (!new)
                return -ENOMEM;

        old = ovsl_dereference(tbl->mask_array);
        if (old) {
                int i;

                for (i = 0; i < old->max; i++) {
                        if (ovsl_dereference(old->masks[i]))
                                new->masks[new->count++] = old->masks[i];
                }
                call_rcu(&old->rcu, mask_array_rcu_cb);
        }

        rcu_assign_pointer(tbl->mask_array, new);

        return 0;
}

static int tbl_mask_array_add_mask(struct flow_table *tbl,
                                   struct sw_flow_mask *new)
{
        struct mask_array *ma = ovsl_dereference(tbl->mask_array);
        int err, ma_count = READ_ONCE(ma->count);

        if (ma_count >= ma->max) {
                err = tbl_mask_array_realloc(tbl, ma->max +
                                                  MASK_ARRAY_SIZE_MIN);
                if (err)
                        return err;

                ma = ovsl_dereference(tbl->mask_array);
        } else {
                /* On every add or delete we need to reset the counters so
                 * every new mask gets a fair chance of being prioritized.
                 */
                tbl_mask_array_reset_counters(ma);
        }

        BUG_ON(ovsl_dereference(ma->masks[ma_count]));

        rcu_assign_pointer(ma->masks[ma_count], new);
        WRITE_ONCE(ma->count, ma_count + 1);

        return 0;
}

static void tbl_mask_array_del_mask(struct flow_table *tbl,
                                    struct sw_flow_mask *mask)
{
        struct mask_array *ma = ovsl_dereference(tbl->mask_array);
        int i, ma_count = READ_ONCE(ma->count);

        /* Remove the deleted mask pointers from the array */
        for (i = 0; i < ma_count; i++) {
                if (mask == ovsl_dereference(ma->masks[i]))
                        goto found;
        }

        BUG();
        return;

found:
        WRITE_ONCE(ma->count, ma_count - 1);

        rcu_assign_pointer(ma->masks[i], ma->masks[ma_count - 1]);
        RCU_INIT_POINTER(ma->masks[ma_count - 1], NULL);

        kfree_rcu(mask, rcu);

        /* Shrink the mask array if necessary. */
        if (ma->max >= (MASK_ARRAY_SIZE_MIN * 2) &&
            ma_count <= (ma->max / 3))
                tbl_mask_array_realloc(tbl, ma->max / 2);
        else
                tbl_mask_array_reset_counters(ma);

}

/* Remove 'mask' from the mask list, if it is not needed any more. */
static void flow_mask_remove(struct flow_table *tbl, struct sw_flow_mask *mask)
{
        if (mask) {
                /* ovs-lock is required to protect mask-refcount and
                 * mask list.
                 */
                ASSERT_OVSL();
                BUG_ON(!mask->ref_count);
                mask->ref_count--;

                if (!mask->ref_count)
                        tbl_mask_array_del_mask(tbl, mask);
        }
}

static void __mask_cache_destroy(struct mask_cache *mc)
{
        free_percpu(mc->mask_cache);
        kfree(mc);
}

static void mask_cache_rcu_cb(struct rcu_head *rcu)
{
        struct mask_cache *mc = container_of(rcu, struct mask_cache, rcu);

        __mask_cache_destroy(mc);
}

static struct mask_cache *tbl_mask_cache_alloc(u32 size)
{
        struct mask_cache_entry __percpu *cache = NULL;
        struct mask_cache *new;

        /* Only allow size to be 0, or a power of 2, and does not exceed
         * percpu allocation size.
         */
        if ((!is_power_of_2(size) && size != 0) ||
            (size * sizeof(struct mask_cache_entry)) > PCPU_MIN_UNIT_SIZE)
                return NULL;

        new = kzalloc(sizeof(*new), GFP_KERNEL);
        if (!new)
                return NULL;

        new->cache_size = size;
        if (new->cache_size > 0) {
                cache = __alloc_percpu(array_size(sizeof(struct mask_cache_entry),
                                                  new->cache_size),
                                       __alignof__(struct mask_cache_entry));
                if (!cache) {
                        kfree(new);
                        return NULL;
                }
        }

        new->mask_cache = cache;
        return new;
}
int ovs_flow_tbl_masks_cache_resize(struct flow_table *table, u32 size)
{
        struct mask_cache *mc = rcu_dereference_ovsl(table->mask_cache);
        struct mask_cache *new;

        if (size == mc->cache_size)
                return 0;

        if ((!is_power_of_2(size) && size != 0) ||
            (size * sizeof(struct mask_cache_entry)) > PCPU_MIN_UNIT_SIZE)
                return -EINVAL;

        new = tbl_mask_cache_alloc(size);
        if (!new)
                return -ENOMEM;

        rcu_assign_pointer(table->mask_cache, new);
        call_rcu(&mc->rcu, mask_cache_rcu_cb);

        return 0;
}

int ovs_flow_tbl_init(struct flow_table *table)
{
        struct table_instance *ti, *ufid_ti;
        struct mask_cache *mc;
        struct mask_array *ma;

        mc = tbl_mask_cache_alloc(MC_DEFAULT_HASH_ENTRIES);
        if (!mc)
                return -ENOMEM;

        ma = tbl_mask_array_alloc(MASK_ARRAY_SIZE_MIN);
        if (!ma)
                goto free_mask_cache;

        ti = table_instance_alloc(TBL_MIN_BUCKETS);
        if (!ti)
                goto free_mask_array;

        ufid_ti = table_instance_alloc(TBL_MIN_BUCKETS);
        if (!ufid_ti)
                goto free_ti;

        rcu_assign_pointer(table->ti, ti);
        rcu_assign_pointer(table->ufid_ti, ufid_ti);
        rcu_assign_pointer(table->mask_array, ma);
        rcu_assign_pointer(table->mask_cache, mc);
        table->last_rehash = jiffies;
        table->count = 0;
        table->ufid_count = 0;
        return 0;

free_ti:
        __table_instance_destroy(ti);
free_mask_array:
        __mask_array_destroy(ma);
free_mask_cache:
        __mask_cache_destroy(mc);
        return -ENOMEM;
}

static void flow_tbl_destroy_rcu_cb(struct rcu_head *rcu)
{
        struct table_instance *ti;

        ti = container_of(rcu, struct table_instance, rcu);
        __table_instance_destroy(ti);
}

static void table_instance_flow_free(struct flow_table *table,
                                     struct table_instance *ti,
                                     struct table_instance *ufid_ti,
                                     struct sw_flow *flow)
{
        hlist_del_rcu(&flow->flow_table.node[ti->node_ver]);
        table->count--;

        if (ovs_identifier_is_ufid(&flow->id)) {
                hlist_del_rcu(&flow->ufid_table.node[ufid_ti->node_ver]);
                table->ufid_count--;
        }

        flow_mask_remove(table, flow->mask);
}

/* Must be called with OVS mutex held. */
void table_instance_flow_flush(struct flow_table *table,
                               struct table_instance *ti,
                               struct table_instance *ufid_ti)
{
        int i;

        for (i = 0; i < ti->n_buckets; i++) {
                struct hlist_head *head = &ti->buckets[i];
                struct hlist_node *n;
                struct sw_flow *flow;

                hlist_for_each_entry_safe(flow, n, head,
                                          flow_table.node[ti->node_ver]) {

                        table_instance_flow_free(table, ti, ufid_ti,
                                                 flow);
                        ovs_flow_free(flow, true);
                }
        }

        if (WARN_ON(table->count != 0 ||
                    table->ufid_count != 0)) {
                table->count = 0;
                table->ufid_count = 0;
        }
}

static void table_instance_destroy(struct table_instance *ti,
                                   struct table_instance *ufid_ti)
{
        call_rcu(&ti->rcu, flow_tbl_destroy_rcu_cb);
        call_rcu(&ufid_ti->rcu, flow_tbl_destroy_rcu_cb);
}

/* No need for locking this function is called from RCU callback or
 * error path.
 */
void ovs_flow_tbl_destroy(struct flow_table *table)
{
        struct table_instance *ti = rcu_dereference_raw(table->ti);
        struct table_instance *ufid_ti = rcu_dereference_raw(table->ufid_ti);
        struct mask_cache *mc = rcu_dereference_raw(table->mask_cache);
        struct mask_array *ma = rcu_dereference_raw(table->mask_array);

        call_rcu(&mc->rcu, mask_cache_rcu_cb);
        call_rcu(&ma->rcu, mask_array_rcu_cb);
        table_instance_destroy(ti, ufid_ti);
}

struct sw_flow *ovs_flow_tbl_dump_next(struct table_instance *ti,
                                       u32 *bucket, u32 *last)
{
        struct sw_flow *flow;
        struct hlist_head *head;
        int ver;
        int i;

        ver = ti->node_ver;
        while (*bucket < ti->n_buckets) {
                i = 0;
                head = &ti->buckets[*bucket];
                hlist_for_each_entry_rcu(flow, head, flow_table.node[ver]) {
                        if (i < *last) {
                                i++;
                                continue;
                        }
                        *last = i + 1;
                        return flow;
                }
                (*bucket)++;
                *last = 0;
        }

        return NULL;
}

static struct hlist_head *find_bucket(struct table_instance *ti, u32 hash)
{
        hash = jhash_1word(hash, ti->hash_seed);
        return &ti->buckets[hash & (ti->n_buckets - 1)];
}

static void table_instance_insert(struct table_instance *ti,
                                  struct sw_flow *flow)
{
        struct hlist_head *head;

        head = find_bucket(ti, flow->flow_table.hash);
        hlist_add_head_rcu(&flow->flow_table.node[ti->node_ver], head);
}

static void ufid_table_instance_insert(struct table_instance *ti,
                                       struct sw_flow *flow)
{
        struct hlist_head *head;

        head = find_bucket(ti, flow->ufid_table.hash);
        hlist_add_head_rcu(&flow->ufid_table.node[ti->node_ver], head);
}

static void flow_table_copy_flows(struct table_instance *old,
                                  struct table_instance *new, bool ufid)
{
        int old_ver;
        int i;

        old_ver = old->node_ver;
        new->node_ver = !old_ver;

        /* Insert in new table. */
        for (i = 0; i < old->n_buckets; i++) {
                struct sw_flow *flow;
                struct hlist_head *head = &old->buckets[i];

                if (ufid)
                        hlist_for_each_entry_rcu(flow, head,
                                                 ufid_table.node[old_ver],
                                                 lockdep_ovsl_is_held())
                                ufid_table_instance_insert(new, flow);
                else
                        hlist_for_each_entry_rcu(flow, head,
                                                 flow_table.node[old_ver],
                                                 lockdep_ovsl_is_held())
                                table_instance_insert(new, flow);
        }
}

static struct table_instance *table_instance_rehash(struct table_instance *ti,
                                                    int n_buckets, bool ufid)
{
        struct table_instance *new_ti;

        new_ti = table_instance_alloc(n_buckets);
        if (!new_ti)
                return NULL;

        flow_table_copy_flows(ti, new_ti, ufid);

        return new_ti;
}

int ovs_flow_tbl_flush(struct flow_table *flow_table)
{
        struct table_instance *old_ti, *new_ti;
        struct table_instance *old_ufid_ti, *new_ufid_ti;

        new_ti = table_instance_alloc(TBL_MIN_BUCKETS);
        if (!new_ti)
                return -ENOMEM;
        new_ufid_ti = table_instance_alloc(TBL_MIN_BUCKETS);
        if (!new_ufid_ti)
                goto err_free_ti;

        old_ti = ovsl_dereference(flow_table->ti);
        old_ufid_ti = ovsl_dereference(flow_table->ufid_ti);

        rcu_assign_pointer(flow_table->ti, new_ti);
        rcu_assign_pointer(flow_table->ufid_ti, new_ufid_ti);
        flow_table->last_rehash = jiffies;

        table_instance_flow_flush(flow_table, old_ti, old_ufid_ti);
        table_instance_destroy(old_ti, old_ufid_ti);
        return 0;

err_free_ti:
        __table_instance_destroy(new_ti);
        return -ENOMEM;
}

static u32 flow_hash(const struct sw_flow_key *key,
                     const struct sw_flow_key_range *range)
{
        const u32 *hash_key = (const u32 *)((const u8 *)key + range->start);

        /* Make sure number of hash bytes are multiple of u32. */
        int hash_u32s = range_n_bytes(range) >> 2;

        return jhash2(hash_key, hash_u32s, 0);
}

static int flow_key_start(const struct sw_flow_key *key)
{
        if (key->tun_proto)
                return 0;
        else
                return rounddown(offsetof(struct sw_flow_key, phy),
                                 sizeof(long));
}

static bool cmp_key(const struct sw_flow_key *key1,
                    const struct sw_flow_key *key2,
                    int key_start, int key_end)
{
        const long *cp1 = (const long *)((const u8 *)key1 + key_start);
        const long *cp2 = (const long *)((const u8 *)key2 + key_start);
        long diffs = 0;
        int i;

        for (i = key_start; i < key_end; i += sizeof(long))
                diffs |= *cp1++ ^ *cp2++;

        return diffs == 0;
}

static bool flow_cmp_masked_key(const struct sw_flow *flow,
                                const struct sw_flow_key *key,
                                const struct sw_flow_key_range *range)
{
        return cmp_key(&flow->key, key, range->start, range->end);
}

static bool ovs_flow_cmp_unmasked_key(const struct sw_flow *flow,
                                      const struct sw_flow_match *match)
{
        struct sw_flow_key *key = match->key;
        int key_start = flow_key_start(key);
        int key_end = match->range.end;

        BUG_ON(ovs_identifier_is_ufid(&flow->id));
        return cmp_key(flow->id.unmasked_key, key, key_start, key_end);
}

static struct sw_flow *masked_flow_lookup(struct table_instance *ti,
                                          const struct sw_flow_key *unmasked,
                                          const struct sw_flow_mask *mask,
                                          u32 *n_mask_hit)
{
        struct sw_flow *flow;
        struct hlist_head *head;
        u32 hash;
        struct sw_flow_key masked_key;

        ovs_flow_mask_key(&masked_key, unmasked, false, mask);
        hash = flow_hash(&masked_key, &mask->range);
        head = find_bucket(ti, hash);
        (*n_mask_hit)++;

        hlist_for_each_entry_rcu(flow, head, flow_table.node[ti->node_ver]) {
                if (flow->mask == mask && flow->flow_table.hash == hash &&
                    flow_cmp_masked_key(flow, &masked_key, &mask->range))
                        return flow;
        }
        return NULL;
}

/* Flow lookup does full lookup on flow table. It starts with
 * mask from index passed in *index.
 * This function MUST be called with BH disabled due to the use
 * of CPU specific variables.
 */
static struct sw_flow *flow_lookup(struct flow_table *tbl,
                                   struct table_instance *ti,
                                   struct mask_array *ma,
                                   const struct sw_flow_key *key,
                                   u32 *n_mask_hit,
                                   u32 *n_cache_hit,
                                   u32 *index)
{
        struct mask_array_stats *stats = this_cpu_ptr(ma->masks_usage_stats);
        struct sw_flow *flow;
        struct sw_flow_mask *mask;
        int i;

        if (likely(*index < ma->max)) {
                mask = rcu_dereference_ovsl(ma->masks[*index]);
                if (mask) {
                        flow = masked_flow_lookup(ti, key, mask, n_mask_hit);
                        if (flow) {
                                u64_stats_update_begin(&stats->syncp);
                                stats->usage_cntrs[*index]++;
                                u64_stats_update_end(&stats->syncp);
                                (*n_cache_hit)++;
                                return flow;
                        }
                }
        }

        for (i = 0; i < ma->max; i++)  {

                if (i == *index)
                        continue;

                mask = rcu_dereference_ovsl(ma->masks[i]);
                if (unlikely(!mask))
                        break;

                flow = masked_flow_lookup(ti, key, mask, n_mask_hit);
                if (flow) { /* Found */
                        *index = i;
                        u64_stats_update_begin(&stats->syncp);
                        stats->usage_cntrs[*index]++;
                        u64_stats_update_end(&stats->syncp);
                        return flow;
                }
        }

        return NULL;
}

/*
 * mask_cache maps flow to probable mask. This cache is not tightly
 * coupled cache, It means updates to  mask list can result in inconsistent
 * cache entry in mask cache.
 * This is per cpu cache and is divided in MC_HASH_SEGS segments.
 * In case of a hash collision the entry is hashed in next segment.
 * */
struct sw_flow *ovs_flow_tbl_lookup_stats(struct flow_table *tbl,
                                          const struct sw_flow_key *key,
                                          u32 skb_hash,
                                          u32 *n_mask_hit,
                                          u32 *n_cache_hit)
{
        struct mask_cache *mc = rcu_dereference(tbl->mask_cache);
        struct mask_array *ma = rcu_dereference(tbl->mask_array);
        struct table_instance *ti = rcu_dereference(tbl->ti);
        struct mask_cache_entry *entries, *ce;
        struct sw_flow *flow;
        u32 hash;
        int seg;

        *n_mask_hit = 0;
        *n_cache_hit = 0;
        if (unlikely(!skb_hash || mc->cache_size == 0)) {
                u32 mask_index = 0;
                u32 cache = 0;

                return flow_lookup(tbl, ti, ma, key, n_mask_hit, &cache,
                                   &mask_index);
        }

        /* Pre and post recirulation flows usually have the same skb_hash
         * value. To avoid hash collisions, rehash the 'skb_hash' with
         * 'recirc_id'.  */
        if (key->recirc_id)
                skb_hash = jhash_1word(skb_hash, key->recirc_id);

        ce = NULL;
        hash = skb_hash;
        entries = this_cpu_ptr(mc->mask_cache);

        /* Find the cache entry 'ce' to operate on. */
        for (seg = 0; seg < MC_HASH_SEGS; seg++) {
                int index = hash & (mc->cache_size - 1);
                struct mask_cache_entry *e;

                e = &entries[index];
                if (e->skb_hash == skb_hash) {
                        flow = flow_lookup(tbl, ti, ma, key, n_mask_hit,
                                           n_cache_hit, &e->mask_index);
                        if (!flow)
                                e->skb_hash = 0;
                        return flow;
                }

                if (!ce || e->skb_hash < ce->skb_hash)
                        ce = e;  /* A better replacement cache candidate. */

                hash >>= MC_HASH_SHIFT;
        }

        /* Cache miss, do full lookup. */
        flow = flow_lookup(tbl, ti, ma, key, n_mask_hit, n_cache_hit,
                           &ce->mask_index);
        if (flow)
                ce->skb_hash = skb_hash;

        *n_cache_hit = 0;
        return flow;
}

struct sw_flow *ovs_flow_tbl_lookup(struct flow_table *tbl,
                                    const struct sw_flow_key *key)
{
        struct table_instance *ti = rcu_dereference_ovsl(tbl->ti);
        struct mask_array *ma = rcu_dereference_ovsl(tbl->mask_array);
        u32 __always_unused n_mask_hit;
        u32 __always_unused n_cache_hit;
        struct sw_flow *flow;
        u32 index = 0;

        /* This function gets called trough the netlink interface and therefore
         * is preemptible. However, flow_lookup() function needs to be called
         * with BH disabled due to CPU specific variables.
         */
        local_bh_disable();
        flow = flow_lookup(tbl, ti, ma, key, &n_mask_hit, &n_cache_hit, &index);
        local_bh_enable();
        return flow;
}

struct sw_flow *ovs_flow_tbl_lookup_exact(struct flow_table *tbl,
                                          const struct sw_flow_match *match)
{
        struct mask_array *ma = ovsl_dereference(tbl->mask_array);
        int i;

        /* Always called under ovs-mutex. */
        for (i = 0; i < ma->max; i++) {
                struct table_instance *ti = rcu_dereference_ovsl(tbl->ti);
                u32 __always_unused n_mask_hit;
                struct sw_flow_mask *mask;
                struct sw_flow *flow;

                mask = ovsl_dereference(ma->masks[i]);
                if (!mask)
                        continue;

                flow = masked_flow_lookup(ti, match->key, mask, &n_mask_hit);
                if (flow && ovs_identifier_is_key(&flow->id) &&
                    ovs_flow_cmp_unmasked_key(flow, match)) {
                        return flow;
                }
        }

        return NULL;
}

static u32 ufid_hash(const struct sw_flow_id *sfid)
{
        return jhash(sfid->ufid, sfid->ufid_len, 0);
}

static bool ovs_flow_cmp_ufid(const struct sw_flow *flow,
                              const struct sw_flow_id *sfid)
{
        if (flow->id.ufid_len != sfid->ufid_len)
                return false;

        return !memcmp(flow->id.ufid, sfid->ufid, sfid->ufid_len);
}

bool ovs_flow_cmp(const struct sw_flow *flow,
                  const struct sw_flow_match *match)
{
        if (ovs_identifier_is_ufid(&flow->id))
                return flow_cmp_masked_key(flow, match->key, &match->range);

        return ovs_flow_cmp_unmasked_key(flow, match);
}

struct sw_flow *ovs_flow_tbl_lookup_ufid(struct flow_table *tbl,
                                         const struct sw_flow_id *ufid)
{
        struct table_instance *ti = rcu_dereference_ovsl(tbl->ufid_ti);
        struct sw_flow *flow;
        struct hlist_head *head;
        u32 hash;

        hash = ufid_hash(ufid);
        head = find_bucket(ti, hash);
        hlist_for_each_entry_rcu(flow, head, ufid_table.node[ti->node_ver]) {
                if (flow->ufid_table.hash == hash &&
                    ovs_flow_cmp_ufid(flow, ufid))
                        return flow;
        }
        return NULL;
}

int ovs_flow_tbl_num_masks(const struct flow_table *table)
{
        struct mask_array *ma = rcu_dereference_ovsl(table->mask_array);
        return READ_ONCE(ma->count);
}

u32 ovs_flow_tbl_masks_cache_size(const struct flow_table *table)
{
        struct mask_cache *mc = rcu_dereference_ovsl(table->mask_cache);

        return READ_ONCE(mc->cache_size);
}

static struct table_instance *table_instance_expand(struct table_instance *ti,
                                                    bool ufid)
{
        return table_instance_rehash(ti, ti->n_buckets * 2, ufid);
}

/* Must be called with OVS mutex held. */
void ovs_flow_tbl_remove(struct flow_table *table, struct sw_flow *flow)
{
        struct table_instance *ti = ovsl_dereference(table->ti);
        struct table_instance *ufid_ti = ovsl_dereference(table->ufid_ti);

        BUG_ON(table->count == 0);
        table_instance_flow_free(table, ti, ufid_ti, flow);
}

static struct sw_flow_mask *mask_alloc(void)
{
        struct sw_flow_mask *mask;

        mask = kmalloc(sizeof(*mask), GFP_KERNEL);
        if (mask)
                mask->ref_count = 1;

        return mask;
}

static bool mask_equal(const struct sw_flow_mask *a,
                       const struct sw_flow_mask *b)
{
        const u8 *a_ = (const u8 *)&a->key + a->range.start;
        const u8 *b_ = (const u8 *)&b->key + b->range.start;

        return  (a->range.end == b->range.end)
                && (a->range.start == b->range.start)
                && (memcmp(a_, b_, range_n_bytes(&a->range)) == 0);
}

static struct sw_flow_mask *flow_mask_find(const struct flow_table *tbl,

                                           const struct sw_flow_mask *mask)
{
        struct mask_array *ma;
        int i;

        ma = ovsl_dereference(tbl->mask_array);
        for (i = 0; i < ma->max; i++) {
                struct sw_flow_mask *t;
                t = ovsl_dereference(ma->masks[i]);

                if (t && mask_equal(mask, t))
                        return t;
        }

        return NULL;
}

/* Add 'mask' into the mask list, if it is not already there. */
static int flow_mask_insert(struct flow_table *tbl, struct sw_flow *flow,
                            const struct sw_flow_mask *new)
{
        struct sw_flow_mask *mask;

        mask = flow_mask_find(tbl, new);
        if (!mask) {
                /* Allocate a new mask if none exsits. */
                mask = mask_alloc();
                if (!mask)
                        return -ENOMEM;
                mask->key = new->key;
                mask->range = new->range;

                /* Add mask to mask-list. */
                if (tbl_mask_array_add_mask(tbl, mask)) {
                        kfree(mask);
                        return -ENOMEM;
                }
        } else {
                BUG_ON(!mask->ref_count);
                mask->ref_count++;
        }

        flow->mask = mask;
        return 0;
}

/* Must be called with OVS mutex held. */
static void flow_key_insert(struct flow_table *table, struct sw_flow *flow)
{
        struct table_instance *new_ti = NULL;
        struct table_instance *ti;

        flow->flow_table.hash = flow_hash(&flow->key, &flow->mask->range);
        ti = ovsl_dereference(table->ti);
        table_instance_insert(ti, flow);
        table->count++;

        /* Expand table, if necessary, to make room. */
        if (table->count > ti->n_buckets)
                new_ti = table_instance_expand(ti, false);
        else if (time_after(jiffies, table->last_rehash + REHASH_INTERVAL))
                new_ti = table_instance_rehash(ti, ti->n_buckets, false);

        if (new_ti) {
                rcu_assign_pointer(table->ti, new_ti);
                call_rcu(&ti->rcu, flow_tbl_destroy_rcu_cb);
                table->last_rehash = jiffies;
        }
}

/* Must be called with OVS mutex held. */
static void flow_ufid_insert(struct flow_table *table, struct sw_flow *flow)
{
        struct table_instance *ti;

        flow->ufid_table.hash = ufid_hash(&flow->id);
        ti = ovsl_dereference(table->ufid_ti);
        ufid_table_instance_insert(ti, flow);
        table->ufid_count++;

        /* Expand table, if necessary, to make room. */
        if (table->ufid_count > ti->n_buckets) {
                struct table_instance *new_ti;

                new_ti = table_instance_expand(ti, true);
                if (new_ti) {
                        rcu_assign_pointer(table->ufid_ti, new_ti);
                        call_rcu(&ti->rcu, flow_tbl_destroy_rcu_cb);
                }
        }
}

/* Must be called with OVS mutex held. */
int ovs_flow_tbl_insert(struct flow_table *table, struct sw_flow *flow,
                        const struct sw_flow_mask *mask)
{
        int err;

        err = flow_mask_insert(table, flow, mask);
        if (err)
                return err;
        flow_key_insert(table, flow);
        if (ovs_identifier_is_ufid(&flow->id))
                flow_ufid_insert(table, flow);

        return 0;
}

static int compare_mask_and_count(const void *a, const void *b)
{
        const struct mask_count *mc_a = a;
        const struct mask_count *mc_b = b;

        return (s64)mc_b->counter - (s64)mc_a->counter;
}

/* Must be called with OVS mutex held. */
void ovs_flow_masks_rebalance(struct flow_table *table)
{
        struct mask_array *ma = rcu_dereference_ovsl(table->mask_array);
        struct mask_count *masks_and_count;
        struct mask_array *new;
        int masks_entries = 0;
        int i;

        /* Build array of all current entries with use counters. */
        masks_and_count = kmalloc_array(ma->max, sizeof(*masks_and_count),
                                        GFP_KERNEL);
        if (!masks_and_count)
                return;

        for (i = 0; i < ma->max; i++) {
                struct sw_flow_mask *mask;
                int cpu;

                mask = rcu_dereference_ovsl(ma->masks[i]);
                if (unlikely(!mask))
                        break;

                masks_and_count[i].index = i;
                masks_and_count[i].counter = 0;

                for_each_possible_cpu(cpu) {
                        struct mask_array_stats *stats;
                        unsigned int start;
                        u64 counter;

                        stats = per_cpu_ptr(ma->masks_usage_stats, cpu);
                        do {
                                start = u64_stats_fetch_begin_irq(&stats->syncp);
                                counter = stats->usage_cntrs[i];
                        } while (u64_stats_fetch_retry_irq(&stats->syncp,
                                                           start));

                        masks_and_count[i].counter += counter;
                }

                /* Subtract the zero count value. */
                masks_and_count[i].counter -= ma->masks_usage_zero_cntr[i];

                /* Rather than calling tbl_mask_array_reset_counters()
                 * below when no change is needed, do it inline here.
                 */
                ma->masks_usage_zero_cntr[i] += masks_and_count[i].counter;
        }

        if (i == 0)
                goto free_mask_entries;

        /* Sort the entries */
        masks_entries = i;
        sort(masks_and_count, masks_entries, sizeof(*masks_and_count),
             compare_mask_and_count, NULL);

        /* If the order is the same, nothing to do... */
        for (i = 0; i < masks_entries; i++) {
                if (i != masks_and_count[i].index)
                        break;
        }
        if (i == masks_entries)
                goto free_mask_entries;

        /* Rebuilt the new list in order of usage. */
        new = tbl_mask_array_alloc(ma->max);
        if (!new)
                goto free_mask_entries;

        for (i = 0; i < masks_entries; i++) {
                int index = masks_and_count[i].index;

                if (ovsl_dereference(ma->masks[index]))
                        new->masks[new->count++] = ma->masks[index];
        }

        rcu_assign_pointer(table->mask_array, new);
        call_rcu(&ma->rcu, mask_array_rcu_cb);

free_mask_entries:
        kfree(masks_and_count);
}

/* Initializes the flow module.
 * Returns zero if successful or a negative error code. */
int ovs_flow_init(void)
{
        BUILD_BUG_ON(__alignof__(struct sw_flow_key) % __alignof__(long));
        BUILD_BUG_ON(sizeof(struct sw_flow_key) % sizeof(long));

        flow_cache = kmem_cache_create("sw_flow", sizeof(struct sw_flow)
                                       + (nr_cpu_ids
                                          * sizeof(struct sw_flow_stats *)),
                                       0, 0, NULL);
        if (flow_cache == NULL)
                return -ENOMEM;

        flow_stats_cache
                = kmem_cache_create("sw_flow_stats", sizeof(struct sw_flow_stats),
                                    0, SLAB_HWCACHE_ALIGN, NULL);
        if (flow_stats_cache == NULL) {
                kmem_cache_destroy(flow_cache);
                flow_cache = NULL;
                return -ENOMEM;
        }

        return 0;
}

/* Uninitializes the flow module. */
void ovs_flow_exit(void)
{
        kmem_cache_destroy(flow_stats_cache);
        kmem_cache_destroy(flow_cache);
}