/*
 * Longest prefix match list implementation
 *
 * Copyright (c) 2016,2017 Daniel Mack
 * Copyright (c) 2016 David Herrmann
 *
 * This file is subject to the terms and conditions of version 2 of the GNU
 * General Public License.  See the file COPYING in the main directory of the
 * Linux distribution for more details.
 */

#include <linux/bpf.h>
#include <linux/err.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <net/ipv6.h>

/* Intermediate node */
#define LPM_TREE_NODE_FLAG_IM BIT(0)

struct lpm_trie_node;

struct lpm_trie_node {
        struct rcu_head rcu;
        struct lpm_trie_node __rcu      *child[2];
        u32                             prefixlen;
        u32                             flags;
        u8                              data[0];
};

struct lpm_trie {
        struct bpf_map                  map;
        struct lpm_trie_node __rcu      *root;
        size_t                          n_entries;
        size_t                          max_prefixlen;
        size_t                          data_size;
        raw_spinlock_t                  lock;
};

/* This trie implements a longest prefix match algorithm that can be used to
 * match IP addresses to a stored set of ranges.
 *
 * Data stored in @data of struct bpf_lpm_key and struct lpm_trie_node is
 * interpreted as big endian, so data[0] stores the most significant byte.
 *
 * Match ranges are internally stored in instances of struct lpm_trie_node
 * which each contain their prefix length as well as two pointers that may
 * lead to more nodes containing more specific matches. Each node also stores
 * a value that is defined by and returned to userspace via the update_elem
 * and lookup functions.
 *
 * For instance, let's start with a trie that was created with a prefix length
 * of 32, so it can be used for IPv4 addresses, and one single element that
 * matches 192.168.0.0/16. The data array would hence contain
 * [0xc0, 0xa8, 0x00, 0x00] in big-endian notation. This documentation will
 * stick to IP-address notation for readability though.
 *
 * As the trie is empty initially, the new node (1) will be places as root
 * node, denoted as (R) in the example below. As there are no other node, both
 * child pointers are %NULL.
 *
 *              +----------------+
 *              |       (1)  (R) |
 *              | 192.168.0.0/16 |
 *              |    value: 1    |
 *              |   [0]    [1]   |
 *              +----------------+
 *
 * Next, let's add a new node (2) matching 192.168.0.0/24. As there is already
 * a node with the same data and a smaller prefix (ie, a less specific one),
 * node (2) will become a child of (1). In child index depends on the next bit
 * that is outside of what (1) matches, and that bit is 0, so (2) will be
 * child[0] of (1):
 *
 *              +----------------+
 *              |       (1)  (R) |
 *              | 192.168.0.0/16 |
 *              |    value: 1    |
 *              |   [0]    [1]   |
 *              +----------------+
 *                   |
 *    +----------------+
 *    |       (2)      |
 *    | 192.168.0.0/24 |
 *    |    value: 2    |
 *    |   [0]    [1]   |
 *    +----------------+
 *
 * The child[1] slot of (1) could be filled with another node which has bit #17
 * (the next bit after the ones that (1) matches on) set to 1. For instance,
 * 192.168.128.0/24:
 *
 *              +----------------+
 *              |       (1)  (R) |
 *              | 192.168.0.0/16 |
 *              |    value: 1    |
 *              |   [0]    [1]   |
 *              +----------------+
 *                   |      |
 *    +----------------+  +------------------+
 *    |       (2)      |  |        (3)       |
 *    | 192.168.0.0/24 |  | 192.168.128.0/24 |
 *    |    value: 2    |  |     value: 3     |
 *    |   [0]    [1]   |  |    [0]    [1]    |
 *    +----------------+  +------------------+
 *
 * Let's add another node (4) to the game for 192.168.1.0/24. In order to place
 * it, node (1) is looked at first, and because (4) of the semantics laid out
 * above (bit #17 is 0), it would normally be attached to (1) as child[0].
 * However, that slot is already allocated, so a new node is needed in between.
 * That node does not have a value attached to it and it will never be
 * returned to users as result of a lookup. It is only there to differentiate
 * the traversal further. It will get a prefix as wide as necessary to
 * distinguish its two children:
 *
 *                      +----------------+
 *                      |       (1)  (R) |
 *                      | 192.168.0.0/16 |
 *                      |    value: 1    |
 *                      |   [0]    [1]   |
 *                      +----------------+
 *                           |      |
 *            +----------------+  +------------------+
 *            |       (4)  (I) |  |        (3)       |
 *            | 192.168.0.0/23 |  | 192.168.128.0/24 |
 *            |    value: ---  |  |     value: 3     |
 *            |   [0]    [1]   |  |    [0]    [1]    |
 *            +----------------+  +------------------+
 *                 |      |
 *  +----------------+  +----------------+
 *  |       (2)      |  |       (5)      |
 *  | 192.168.0.0/24 |  | 192.168.1.0/24 |
 *  |    value: 2    |  |     value: 5   |
 *  |   [0]    [1]   |  |   [0]    [1]   |
 *  +----------------+  +----------------+
 *
 * 192.168.1.1/32 would be a child of (5) etc.
 *
 * An intermediate node will be turned into a 'real' node on demand. In the
 * example above, (4) would be re-used if 192.168.0.0/23 is added to the trie.
 *
 * A fully populated trie would have a height of 32 nodes, as the trie was
 * created with a prefix length of 32.
 *
 * The lookup starts at the root node. If the current node matches and if there
 * is a child that can be used to become more specific, the trie is traversed
 * downwards. The last node in the traversal that is a non-intermediate one is
 * returned.
 */

static inline int extract_bit(const u8 *data, size_t index)
{
        return !!(data[index / 8] & (1 << (7 - (index % 8))));
}

/**
 * longest_prefix_match() - determine the longest prefix
 * @trie:       The trie to get internal sizes from
 * @node:       The node to operate on
 * @key:        The key to compare to @node
 *
 * Determine the longest prefix of @node that matches the bits in @key.
 */
static size_t longest_prefix_match(const struct lpm_trie *trie,
                                   const struct lpm_trie_node *node,
                                   const struct bpf_lpm_trie_key *key)
{
        size_t prefixlen = 0;
        size_t i;

        for (i = 0; i < trie->data_size; i++) {
                size_t b;

                b = 8 - fls(node->data[i] ^ key->data[i]);
                prefixlen += b;

                if (prefixlen >= node->prefixlen || prefixlen >= key->prefixlen)
                        return min(node->prefixlen, key->prefixlen);

                if (b < 8)
                        break;
        }

        return prefixlen;
}

/* Called from syscall or from eBPF program */
static void *trie_lookup_elem(struct bpf_map *map, void *_key)
{
        struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
        struct lpm_trie_node *node, *found = NULL;
        struct bpf_lpm_trie_key *key = _key;

        /* Start walking the trie from the root node ... */

        for (node = rcu_dereference(trie->root); node;) {
                unsigned int next_bit;
                size_t matchlen;

                /* Determine the longest prefix of @node that matches @key.
                 * If it's the maximum possible prefix for this trie, we have
                 * an exact match and can return it directly.
                 */
                matchlen = longest_prefix_match(trie, node, key);
                if (matchlen == trie->max_prefixlen) {
                        found = node;
                        break;
                }

                /* If the number of bits that match is smaller than the prefix
                 * length of @node, bail out and return the node we have seen
                 * last in the traversal (ie, the parent).
                 */
                if (matchlen < node->prefixlen)
                        break;

                /* Consider this node as return candidate unless it is an
                 * artificially added intermediate one.
                 */
                if (!(node->flags & LPM_TREE_NODE_FLAG_IM))
                        found = node;

                /* If the node match is fully satisfied, let's see if we can
                 * become more specific. Determine the next bit in the key and
                 * traverse down.
                 */
                next_bit = extract_bit(key->data, node->prefixlen);
                node = rcu_dereference(node->child[next_bit]);
        }

        if (!found)
                return NULL;

        return found->data + trie->data_size;
}

static struct lpm_trie_node *lpm_trie_node_alloc(const struct lpm_trie *trie,
                                                 const void *value)
{
        struct lpm_trie_node *node;
        size_t size = sizeof(struct lpm_trie_node) + trie->data_size;

        if (value)
                size += trie->map.value_size;

        node = kmalloc_node(size, GFP_ATOMIC | __GFP_NOWARN,
                            trie->map.numa_node);
        if (!node)
                return NULL;

        node->flags = 0;

        if (value)
                memcpy(node->data + trie->data_size, value,
                       trie->map.value_size);

        return node;
}

/* Called from syscall or from eBPF program */
static int trie_update_elem(struct bpf_map *map,
                            void *_key, void *value, u64 flags)
{
        struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
        struct lpm_trie_node *node, *im_node = NULL, *new_node = NULL;
        struct lpm_trie_node __rcu **slot;
        struct bpf_lpm_trie_key *key = _key;
        unsigned long irq_flags;
        unsigned int next_bit;
        size_t matchlen = 0;
        int ret = 0;

        if (unlikely(flags > BPF_EXIST))
                return -EINVAL;

        if (key->prefixlen > trie->max_prefixlen)
                return -EINVAL;

        raw_spin_lock_irqsave(&trie->lock, irq_flags);

        /* Allocate and fill a new node */

        if (trie->n_entries == trie->map.max_entries) {
                ret = -ENOSPC;
                goto out;
        }

        new_node = lpm_trie_node_alloc(trie, value);
        if (!new_node) {
                ret = -ENOMEM;
                goto out;
        }

        trie->n_entries++;

        new_node->prefixlen = key->prefixlen;
        RCU_INIT_POINTER(new_node->child[0], NULL);
        RCU_INIT_POINTER(new_node->child[1], NULL);
        memcpy(new_node->data, key->data, trie->data_size);

        /* Now find a slot to attach the new node. To do that, walk the tree
         * from the root and match as many bits as possible for each node until
         * we either find an empty slot or a slot that needs to be replaced by
         * an intermediate node.
         */
        slot = &trie->root;

        while ((node = rcu_dereference_protected(*slot,
                                        lockdep_is_held(&trie->lock)))) {
                matchlen = longest_prefix_match(trie, node, key);

                if (node->prefixlen != matchlen ||
                    node->prefixlen == key->prefixlen ||
                    node->prefixlen == trie->max_prefixlen)
                        break;

                next_bit = extract_bit(key->data, node->prefixlen);
                slot = &node->child[next_bit];
        }

        /* If the slot is empty (a free child pointer or an empty root),
         * simply assign the @new_node to that slot and be done.
         */
        if (!node) {
                rcu_assign_pointer(*slot, new_node);
                goto out;
        }

        /* If the slot we picked already exists, replace it with @new_node
         * which already has the correct data array set.
         */
        if (node->prefixlen == matchlen) {
                new_node->child[0] = node->child[0];
                new_node->child[1] = node->child[1];

                if (!(node->flags & LPM_TREE_NODE_FLAG_IM))
                        trie->n_entries--;

                rcu_assign_pointer(*slot, new_node);
                kfree_rcu(node, rcu);

                goto out;
        }

        /* If the new node matches the prefix completely, it must be inserted
         * as an ancestor. Simply insert it between @node and *@slot.
         */
        if (matchlen == key->prefixlen) {
                next_bit = extract_bit(node->data, matchlen);
                rcu_assign_pointer(new_node->child[next_bit], node);
                rcu_assign_pointer(*slot, new_node);
                goto out;
        }

        im_node = lpm_trie_node_alloc(trie, NULL);
        if (!im_node) {
                ret = -ENOMEM;
                goto out;
        }

        im_node->prefixlen = matchlen;
        im_node->flags |= LPM_TREE_NODE_FLAG_IM;
        memcpy(im_node->data, node->data, trie->data_size);

        /* Now determine which child to install in which slot */
        if (extract_bit(key->data, matchlen)) {
                rcu_assign_pointer(im_node->child[0], node);
                rcu_assign_pointer(im_node->child[1], new_node);
        } else {
                rcu_assign_pointer(im_node->child[0], new_node);
                rcu_assign_pointer(im_node->child[1], node);
        }

        /* Finally, assign the intermediate node to the determined spot */
        rcu_assign_pointer(*slot, im_node);

out:
        if (ret) {
                if (new_node)
                        trie->n_entries--;

                kfree(new_node);
                kfree(im_node);
        }

        raw_spin_unlock_irqrestore(&trie->lock, irq_flags);

        return ret;
}

static int trie_delete_elem(struct bpf_map *map, void *key)
{
        /* TODO */
        return -ENOSYS;
}

#define LPM_DATA_SIZE_MAX       256
#define LPM_DATA_SIZE_MIN       1

#define LPM_VAL_SIZE_MAX        (KMALLOC_MAX_SIZE - LPM_DATA_SIZE_MAX - \
                                 sizeof(struct lpm_trie_node))
#define LPM_VAL_SIZE_MIN        1

#define LPM_KEY_SIZE(X)         (sizeof(struct bpf_lpm_trie_key) + (X))
#define LPM_KEY_SIZE_MAX        LPM_KEY_SIZE(LPM_DATA_SIZE_MAX)
#define LPM_KEY_SIZE_MIN        LPM_KEY_SIZE(LPM_DATA_SIZE_MIN)

#define LPM_CREATE_FLAG_MASK    (BPF_F_NO_PREALLOC | BPF_F_NUMA_NODE)

static struct bpf_map *trie_alloc(union bpf_attr *attr)
{
        struct lpm_trie *trie;
        u64 cost = sizeof(*trie), cost_per_node;
        int ret;

        if (!capable(CAP_SYS_ADMIN))
                return ERR_PTR(-EPERM);

        /* check sanity of attributes */
        if (attr->max_entries == 0 ||
            !(attr->map_flags & BPF_F_NO_PREALLOC) ||
            attr->map_flags & ~LPM_CREATE_FLAG_MASK ||
            attr->key_size < LPM_KEY_SIZE_MIN ||
            attr->key_size > LPM_KEY_SIZE_MAX ||
            attr->value_size < LPM_VAL_SIZE_MIN ||
            attr->value_size > LPM_VAL_SIZE_MAX)
                return ERR_PTR(-EINVAL);

        trie = kzalloc(sizeof(*trie), GFP_USER | __GFP_NOWARN);
        if (!trie)
                return ERR_PTR(-ENOMEM);

        /* copy mandatory map attributes */
        trie->map.map_type = attr->map_type;
        trie->map.key_size = attr->key_size;
        trie->map.value_size = attr->value_size;
        trie->map.max_entries = attr->max_entries;
        trie->map.map_flags = attr->map_flags;
        trie->map.numa_node = bpf_map_attr_numa_node(attr);
        trie->data_size = attr->key_size -
                          offsetof(struct bpf_lpm_trie_key, data);
        trie->max_prefixlen = trie->data_size * 8;

        cost_per_node = sizeof(struct lpm_trie_node) +
                        attr->value_size + trie->data_size;
        cost += (u64) attr->max_entries * cost_per_node;
        if (cost >= U32_MAX - PAGE_SIZE) {
                ret = -E2BIG;
                goto out_err;
        }

        trie->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;

        ret = bpf_map_precharge_memlock(trie->map.pages);
        if (ret)
                goto out_err;

        raw_spin_lock_init(&trie->lock);

        return &trie->map;
out_err:
        kfree(trie);
        return ERR_PTR(ret);
}

static void trie_free(struct bpf_map *map)
{
        struct lpm_trie *trie = container_of(map, struct lpm_trie, map);
        struct lpm_trie_node __rcu **slot;
        struct lpm_trie_node *node;

        raw_spin_lock(&trie->lock);

        /* Always start at the root and walk down to a node that has no
         * children. Then free that node, nullify its reference in the parent
         * and start over.
         */

        for (;;) {
                slot = &trie->root;

                for (;;) {
                        node = rcu_dereference_protected(*slot,
                                        lockdep_is_held(&trie->lock));
                        if (!node)
                                goto unlock;

                        if (rcu_access_pointer(node->child[0])) {
                                slot = &node->child[0];
                                continue;
                        }

                        if (rcu_access_pointer(node->child[1])) {
                                slot = &node->child[1];
                                continue;
                        }

                        kfree(node);
                        RCU_INIT_POINTER(*slot, NULL);
                        break;
                }
        }

unlock:
        raw_spin_unlock(&trie->lock);
}

static int trie_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
        return -ENOTSUPP;
}

const struct bpf_map_ops trie_map_ops = {
        .map_alloc = trie_alloc,
        .map_free = trie_free,
        .map_get_next_key = trie_get_next_key,
        .map_lookup_elem = trie_lookup_elem,
        .map_update_elem = trie_update_elem,
        .map_delete_elem = trie_delete_elem,
};