/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
 *
 * 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.
 */
#include <linux/bpf.h>
#include <linux/jhash.h>
#include <linux/filter.h>
#include <linux/vmalloc.h>

struct bpf_htab {
        struct bpf_map map;
        struct hlist_head *buckets;
        spinlock_t lock;
        u32 count;      /* number of elements in this hashtable */
        u32 n_buckets;  /* number of hash buckets */
        u32 elem_size;  /* size of each element in bytes */
};

/* each htab element is struct htab_elem + key + value */
struct htab_elem {
        struct hlist_node hash_node;
        struct rcu_head rcu;
        u32 hash;
        char key[0] __aligned(8);
};

/* Called from syscall */
static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
{
        struct bpf_htab *htab;
        int err, i;

        htab = kzalloc(sizeof(*htab), GFP_USER);
        if (!htab)
                return ERR_PTR(-ENOMEM);

        /* mandatory map attributes */
        htab->map.key_size = attr->key_size;
        htab->map.value_size = attr->value_size;
        htab->map.max_entries = attr->max_entries;

        /* check sanity of attributes.
         * value_size == 0 may be allowed in the future to use map as a set
         */
        err = -EINVAL;
        if (htab->map.max_entries == 0 || htab->map.key_size == 0 ||
            htab->map.value_size == 0)
                goto free_htab;

        /* hash table size must be power of 2 */
        htab->n_buckets = roundup_pow_of_two(htab->map.max_entries);

        err = -E2BIG;
        if (htab->map.key_size > MAX_BPF_STACK)
                /* eBPF programs initialize keys on stack, so they cannot be
                 * larger than max stack size
                 */
                goto free_htab;

        err = -ENOMEM;
        /* prevent zero size kmalloc and check for u32 overflow */
        if (htab->n_buckets == 0 ||
            htab->n_buckets > U32_MAX / sizeof(struct hlist_head))
                goto free_htab;

        htab->buckets = kmalloc_array(htab->n_buckets, sizeof(struct hlist_head),
                                      GFP_USER | __GFP_NOWARN);

        if (!htab->buckets) {
                htab->buckets = vmalloc(htab->n_buckets * sizeof(struct hlist_head));
                if (!htab->buckets)
                        goto free_htab;
        }

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

        spin_lock_init(&htab->lock);
        htab->count = 0;

        htab->elem_size = sizeof(struct htab_elem) +
                          round_up(htab->map.key_size, 8) +
                          htab->map.value_size;
        return &htab->map;

free_htab:
        kfree(htab);
        return ERR_PTR(err);
}

static inline u32 htab_map_hash(const void *key, u32 key_len)
{
        return jhash(key, key_len, 0);
}

static inline struct hlist_head *select_bucket(struct bpf_htab *htab, u32 hash)
{
        return &htab->buckets[hash & (htab->n_buckets - 1)];
}

static struct htab_elem *lookup_elem_raw(struct hlist_head *head, u32 hash,
                                         void *key, u32 key_size)
{
        struct htab_elem *l;

        hlist_for_each_entry_rcu(l, head, hash_node)
                if (l->hash == hash && !memcmp(&l->key, key, key_size))
                        return l;

        return NULL;
}

/* Called from syscall or from eBPF program */
static void *htab_map_lookup_elem(struct bpf_map *map, void *key)
{
        struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
        struct hlist_head *head;
        struct htab_elem *l;
        u32 hash, key_size;

        /* Must be called with rcu_read_lock. */
        WARN_ON_ONCE(!rcu_read_lock_held());

        key_size = map->key_size;

        hash = htab_map_hash(key, key_size);

        head = select_bucket(htab, hash);

        l = lookup_elem_raw(head, hash, key, key_size);

        if (l)
                return l->key + round_up(map->key_size, 8);

        return NULL;
}

/* Called from syscall */
static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
        struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
        struct hlist_head *head;
        struct htab_elem *l, *next_l;
        u32 hash, key_size;
        int i;

        WARN_ON_ONCE(!rcu_read_lock_held());

        key_size = map->key_size;

        hash = htab_map_hash(key, key_size);

        head = select_bucket(htab, hash);

        /* lookup the key */
        l = lookup_elem_raw(head, hash, key, key_size);

        if (!l) {
                i = 0;
                goto find_first_elem;
        }

        /* key was found, get next key in the same bucket */
        next_l = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(&l->hash_node)),
                                  struct htab_elem, hash_node);

        if (next_l) {
                /* if next elem in this hash list is non-zero, just return it */
                memcpy(next_key, next_l->key, key_size);
                return 0;
        }

        /* no more elements in this hash list, go to the next bucket */
        i = hash & (htab->n_buckets - 1);
        i++;

find_first_elem:
        /* iterate over buckets */
        for (; i < htab->n_buckets; i++) {
                head = select_bucket(htab, i);

                /* pick first element in the bucket */
                next_l = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),
                                          struct htab_elem, hash_node);
                if (next_l) {
                        /* if it's not empty, just return it */
                        memcpy(next_key, next_l->key, key_size);
                        return 0;
                }
        }

        /* itereated over all buckets and all elements */
        return -ENOENT;
}

/* Called from syscall or from eBPF program */
static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
                                u64 map_flags)
{
        struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
        struct htab_elem *l_new, *l_old;
        struct hlist_head *head;
        unsigned long flags;
        u32 key_size;
        int ret;

        if (map_flags > BPF_EXIST)
                /* unknown flags */
                return -EINVAL;

        WARN_ON_ONCE(!rcu_read_lock_held());

        /* allocate new element outside of lock */
        l_new = kmalloc(htab->elem_size, GFP_ATOMIC);
        if (!l_new)
                return -ENOMEM;

        key_size = map->key_size;

        memcpy(l_new->key, key, key_size);
        memcpy(l_new->key + round_up(key_size, 8), value, map->value_size);

        l_new->hash = htab_map_hash(l_new->key, key_size);

        /* bpf_map_update_elem() can be called in_irq() */
        spin_lock_irqsave(&htab->lock, flags);

        head = select_bucket(htab, l_new->hash);

        l_old = lookup_elem_raw(head, l_new->hash, key, key_size);

        if (!l_old && unlikely(htab->count >= map->max_entries)) {
                /* if elem with this 'key' doesn't exist and we've reached
                 * max_entries limit, fail insertion of new elem
                 */
                ret = -E2BIG;
                goto err;
        }

        if (l_old && map_flags == BPF_NOEXIST) {
                /* elem already exists */
                ret = -EEXIST;
                goto err;
        }

        if (!l_old && map_flags == BPF_EXIST) {
                /* elem doesn't exist, cannot update it */
                ret = -ENOENT;
                goto err;
        }

        /* add new element to the head of the list, so that concurrent
         * search will find it before old elem
         */
        hlist_add_head_rcu(&l_new->hash_node, head);
        if (l_old) {
                hlist_del_rcu(&l_old->hash_node);
                kfree_rcu(l_old, rcu);
        } else {
                htab->count++;
        }
        spin_unlock_irqrestore(&htab->lock, flags);

        return 0;
err:
        spin_unlock_irqrestore(&htab->lock, flags);
        kfree(l_new);
        return ret;
}

/* Called from syscall or from eBPF program */
static int htab_map_delete_elem(struct bpf_map *map, void *key)
{
        struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
        struct hlist_head *head;
        struct htab_elem *l;
        unsigned long flags;
        u32 hash, key_size;
        int ret = -ENOENT;

        WARN_ON_ONCE(!rcu_read_lock_held());

        key_size = map->key_size;

        hash = htab_map_hash(key, key_size);

        spin_lock_irqsave(&htab->lock, flags);

        head = select_bucket(htab, hash);

        l = lookup_elem_raw(head, hash, key, key_size);

        if (l) {
                hlist_del_rcu(&l->hash_node);
                htab->count--;
                kfree_rcu(l, rcu);
                ret = 0;
        }

        spin_unlock_irqrestore(&htab->lock, flags);
        return ret;
}

static void delete_all_elements(struct bpf_htab *htab)
{
        int i;

        for (i = 0; i < htab->n_buckets; i++) {
                struct hlist_head *head = select_bucket(htab, i);
                struct hlist_node *n;
                struct htab_elem *l;

                hlist_for_each_entry_safe(l, n, head, hash_node) {
                        hlist_del_rcu(&l->hash_node);
                        htab->count--;
                        kfree(l);
                }
        }
}

/* Called when map->refcnt goes to zero, either from workqueue or from syscall */
static void htab_map_free(struct bpf_map *map)
{
        struct bpf_htab *htab = container_of(map, struct bpf_htab, map);

        /* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
         * so the programs (can be more than one that used this map) were
         * disconnected from events. Wait for outstanding critical sections in
         * these programs to complete
         */
        synchronize_rcu();

        /* some of kfree_rcu() callbacks for elements of this map may not have
         * executed. It's ok. Proceed to free residual elements and map itself
         */
        delete_all_elements(htab);
        kvfree(htab->buckets);
        kfree(htab);
}

static const struct bpf_map_ops htab_ops = {
        .map_alloc = htab_map_alloc,
        .map_free = htab_map_free,
        .map_get_next_key = htab_map_get_next_key,
        .map_lookup_elem = htab_map_lookup_elem,
        .map_update_elem = htab_map_update_elem,
        .map_delete_elem = htab_map_delete_elem,
};

static struct bpf_map_type_list htab_type __read_mostly = {
        .ops = &htab_ops,
        .type = BPF_MAP_TYPE_HASH,
};

static int __init register_htab_map(void)
{
        bpf_register_map_type(&htab_type);
        return 0;
}
late_initcall(register_htab_map);