/* 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;
};

static inline htab_bucket_t *__select_bucket(struct htab __arena *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(struct htab __arena *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(struct htab __arena *htab, 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(struct htab __arena *htab, 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(struct htab __arena *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);
}