/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) */
/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
#pragma once
#include <errno.h>
#include "bpf_arena_alloc.h"
#include "bpf_arena_list.h"

struct htab_bucket {
        struct arena_list_head head;
};
typedef struct htab_bucket __arena htab_bucket_t;

struct htab {
        htab_bucket_t *buckets;
        int n_buckets;
};
typedef struct htab __arena htab_t;

static inline htab_bucket_t *__select_bucket(htab_t *htab, __u32 hash)
{
        htab_bucket_t *b = htab->buckets;

        cast_kern(b);
        return &b[hash & (htab->n_buckets - 1)];
}

static inline arena_list_head_t *select_bucket(htab_t *htab, __u32 hash)
{
        return &__select_bucket(htab, hash)->head;
}

struct hashtab_elem {
        int hash;
        int key;
        int value;
        struct arena_list_node hash_node;
};
typedef struct hashtab_elem __arena hashtab_elem_t;

static hashtab_elem_t *lookup_elem_raw(arena_list_head_t *head, __u32 hash, int key)
{
        hashtab_elem_t *l;

        list_for_each_entry(l, head, hash_node)
                if (l->hash == hash && l->key == key)
                        return l;

        return NULL;
}

static int htab_hash(int key)
{
        return key;
}

__weak int htab_lookup_elem(htab_t *htab __arg_arena, int key)
{
        hashtab_elem_t *l_old;
        arena_list_head_t *head;

        cast_kern(htab);
        head = select_bucket(htab, key);
        l_old = lookup_elem_raw(head, htab_hash(key), key);
        if (l_old)
                return l_old->value;
        return 0;
}

__weak int htab_update_elem(htab_t *htab __arg_arena, int key, int value)
{
        hashtab_elem_t *l_new = NULL, *l_old;
        arena_list_head_t *head;

        cast_kern(htab);
        head = select_bucket(htab, key);
        l_old = lookup_elem_raw(head, htab_hash(key), key);

        l_new = bpf_alloc(sizeof(*l_new));
        if (!l_new)
                return -ENOMEM;
        l_new->key = key;
        l_new->hash = htab_hash(key);
        l_new->value = value;

        list_add_head(&l_new->hash_node, head);
        if (l_old) {
                list_del(&l_old->hash_node);
                bpf_free(l_old);
        }
        return 0;
}

void htab_init(htab_t *htab)
{
        void __arena *buckets = bpf_arena_alloc_pages(&arena, NULL, 2, NUMA_NO_NODE, 0);

        cast_user(buckets);
        htab->buckets = buckets;
        htab->n_buckets = 2 * PAGE_SIZE / sizeof(struct htab_bucket);
}