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    Subject[PATCH RFC net-next 06/14] bpf: add hashtable type of BPF maps
    Date
    add new map type: BPF_MAP_TYPE_HASH
    and its simple (not auto resizeable) hash table implementation

    Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
    ---
    include/uapi/linux/bpf.h | 1 +
    kernel/bpf/Makefile | 2 +-
    kernel/bpf/hashtab.c | 371 ++++++++++++++++++++++++++++++++++++++++++++++
    3 files changed, 373 insertions(+), 1 deletion(-)
    create mode 100644 kernel/bpf/hashtab.c

    diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
    index faed2ce2d25a..1399ed1d5dad 100644
    --- a/include/uapi/linux/bpf.h
    +++ b/include/uapi/linux/bpf.h
    @@ -354,6 +354,7 @@ enum bpf_map_attributes {

    enum bpf_map_type {
    BPF_MAP_TYPE_UNSPEC,
    + BPF_MAP_TYPE_HASH,
    };

    #endif /* _UAPI__LINUX_BPF_H__ */
    diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
    index e9f7334ed07a..558e12712ebc 100644
    --- a/kernel/bpf/Makefile
    +++ b/kernel/bpf/Makefile
    @@ -1 +1 @@
    -obj-y := core.o syscall.o
    +obj-y := core.o syscall.o hashtab.o
    diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
    new file mode 100644
    index 000000000000..6e481cacbba3
    --- /dev/null
    +++ b/kernel/bpf/hashtab.c
    @@ -0,0 +1,371 @@
    +/* 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 <net/netlink.h>
    +#include <linux/jhash.h>
    +
    +struct bpf_htab {
    + struct bpf_map map;
    + struct hlist_head *buckets;
    + struct kmem_cache *elem_cache;
    + char *slab_name;
    + 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;
    + struct bpf_htab *htab;
    + u32 hash;
    + u32 pad;
    + char key[0];
    +};
    +
    +#define HASH_MAX_BUCKETS 1024
    +#define BPF_MAP_MAX_KEY_SIZE 256
    +static struct bpf_map *htab_map_alloc(struct nlattr *attr[BPF_MAP_ATTR_MAX + 1])
    +{
    + struct bpf_htab *htab;
    + int err, i;
    +
    + htab = kmalloc(sizeof(*htab), GFP_USER);
    + if (!htab)
    + return ERR_PTR(-ENOMEM);
    +
    + /* look for mandatory map attributes */
    + err = -EINVAL;
    + if (!attr[BPF_MAP_KEY_SIZE])
    + goto free_htab;
    + htab->map.key_size = nla_get_u32(attr[BPF_MAP_KEY_SIZE]);
    +
    + if (!attr[BPF_MAP_VALUE_SIZE])
    + goto free_htab;
    + htab->map.value_size = nla_get_u32(attr[BPF_MAP_VALUE_SIZE]);
    +
    + if (!attr[BPF_MAP_MAX_ENTRIES])
    + goto free_htab;
    + htab->map.max_entries = nla_get_u32(attr[BPF_MAP_MAX_ENTRIES]);
    +
    + htab->n_buckets = (htab->map.max_entries <= HASH_MAX_BUCKETS) ?
    + htab->map.max_entries : HASH_MAX_BUCKETS;
    +
    + /* hash table size must be power of 2 */
    + if ((htab->n_buckets & (htab->n_buckets - 1)) != 0)
    + goto free_htab;
    +
    + err = -E2BIG;
    + if (htab->map.key_size > BPF_MAP_MAX_KEY_SIZE)
    + goto free_htab;
    +
    + err = -ENOMEM;
    + htab->buckets = kmalloc(htab->n_buckets * sizeof(struct hlist_head),
    + GFP_USER);
    +
    + 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;
    +
    + htab->slab_name = kasprintf(GFP_USER, "bpf_htab_%p", htab);
    + if (!htab->slab_name)
    + goto free_buckets;
    +
    + htab->elem_cache = kmem_cache_create(htab->slab_name,
    + htab->elem_size, 0, 0, NULL);
    + if (!htab->elem_cache)
    + goto free_slab_name;
    +
    + return &htab->map;
    +
    +free_slab_name:
    + kfree(htab->slab_name);
    +free_buckets:
    + kfree(htab->buckets);
    +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;
    +}
    +
    +/* Must be called with rcu_read_lock. */
    +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;
    +
    + 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);
    + else
    + return NULL;
    +}
    +
    +/* Must be called with rcu_read_lock. */
    +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;
    + } else {
    + /* 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;
    +}
    +
    +static struct htab_elem *htab_alloc_elem(struct bpf_htab *htab)
    +{
    + void *l;
    +
    + l = kmem_cache_alloc(htab->elem_cache, GFP_ATOMIC);
    + if (!l)
    + return ERR_PTR(-ENOMEM);
    + return l;
    +}
    +
    +static void free_htab_elem_rcu(struct rcu_head *rcu)
    +{
    + struct htab_elem *l = container_of(rcu, struct htab_elem, rcu);
    +
    + kmem_cache_free(l->htab->elem_cache, l);
    +}
    +
    +static void release_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
    +{
    + l->htab = htab;
    + call_rcu(&l->rcu, free_htab_elem_rcu);
    +}
    +
    +/* Must be called with rcu_read_lock. */
    +static int htab_map_update_elem(struct bpf_map *map, void *key, void *value)
    +{
    + struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
    + struct htab_elem *l_new, *l_old;
    + struct hlist_head *head;
    + u32 key_size;
    +
    + WARN_ON_ONCE(!rcu_read_lock_held());
    +
    + l_new = htab_alloc_elem(htab);
    + if (IS_ERR(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);
    +
    + head = select_bucket(htab, l_new->hash);
    +
    + l_old = lookup_elem_raw(head, l_new->hash, key, key_size);
    +
    + spin_lock_bh(&htab->lock);
    + 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
    + */
    + spin_unlock_bh(&htab->lock);
    + kmem_cache_free(htab->elem_cache, l_new);
    + return -EFBIG;
    + }
    +
    + /* 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);
    + release_htab_elem(htab, l_old);
    + } else {
    + htab->count++;
    + }
    + spin_unlock_bh(&htab->lock);
    +
    + return 0;
    +}
    +
    +/* Must be called with rcu_read_lock. */
    +static int htab_map_delete_elem(struct bpf_map *map, void *key)
    +{
    + struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
    + struct htab_elem *l;
    + struct hlist_head *head;
    + u32 hash, key_size;
    +
    + 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) {
    + spin_lock_bh(&htab->lock);
    + hlist_del_rcu(&l->hash_node);
    + htab->count--;
    + release_htab_elem(htab, l);
    + spin_unlock_bh(&htab->lock);
    + return 0;
    + }
    + return -ESRCH;
    +}
    +
    +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--;
    + kmem_cache_free(htab->elem_cache, l);
    + }
    + }
    +}
    +
    +/* called when map->refcnt goes to zero */
    +static void htab_map_free(struct bpf_map *map)
    +{
    + struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
    +
    + /* wait for all outstanding updates to complete */
    + synchronize_rcu();
    +
    + /* kmem_cache_free all htab elements */
    + delete_all_elements(htab);
    +
    + /* and destroy cache, which might sleep */
    + kmem_cache_destroy(htab->elem_cache);
    +
    + kfree(htab->buckets);
    + kfree(htab->slab_name);
    + kfree(htab);
    +}
    +
    +static 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 tl = {
    + .ops = &htab_ops,
    + .type = BPF_MAP_TYPE_HASH,
    +};
    +
    +static int __init register_htab_map(void)
    +{
    + bpf_register_map_type(&tl);
    + return 0;
    +}
    +late_initcall(register_htab_map);
    --
    1.7.9.5


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