/* SPDX-License-Identifier: GPL-2.0 */

#ifndef BTRFS_LRU_CACHE_H
#define BTRFS_LRU_CACHE_H

#include <linux/types.h>
#include <linux/maple_tree.h>
#include <linux/list.h>

/*
 * A cache entry. This is meant to be embedded in a structure of a user of
 * this module. Similar to how struct list_head and struct rb_node are used.
 *
 * Note: it should be embedded as the first element in a struct (offset 0), and
 * this module assumes it was allocated with kmalloc(), so it calls kfree() when
 * it needs to free an entry.
 */
struct btrfs_lru_cache_entry {
        struct list_head lru_list;
        u64 key;
        /*
         * Optional generation associated to a key. Use 0 if not needed/used.
         * Entries with the same key and different generations are stored in a
         * linked list, so use this only for cases where there's a small number
         * of different generations.
         */
        u64 gen;
        /*
         * The maple tree uses unsigned long type for the keys, which is 32 bits
         * on 32 bits systems, and 64 bits on 64 bits systems. So if we want to
         * use something like inode numbers as keys, which are always a u64, we
         * have to deal with this in a special way - we store the key in the
         * entry itself, as a u64, and the values inserted into the maple tree
         * are linked lists of entries - so in case we are on a 64 bits system,
         * that list always has a single entry, while on 32 bits systems it
         * may have more than one, with each entry having the same value for
         * their lower 32 bits of the u64 key.
         */
        struct list_head list;
};

struct btrfs_lru_cache {
        struct list_head lru_list;
        struct maple_tree entries;
        /* Number of entries stored in the cache. */
        unsigned int size;
        /* Maximum number of entries the cache can have. */
        unsigned int max_size;
};

#define btrfs_lru_cache_for_each_entry_safe(cache, entry, tmp)          \
        list_for_each_entry_safe_reverse((entry), (tmp), &(cache)->lru_list, lru_list)

static inline struct btrfs_lru_cache_entry *btrfs_lru_cache_lru_entry(
                                              struct btrfs_lru_cache *cache)
{
        return list_first_entry_or_null(&cache->lru_list,
                                        struct btrfs_lru_cache_entry, lru_list);
}

void btrfs_lru_cache_init(struct btrfs_lru_cache *cache, unsigned int max_size);
struct btrfs_lru_cache_entry *btrfs_lru_cache_lookup(struct btrfs_lru_cache *cache,
                                                     u64 key, u64 gen);
int btrfs_lru_cache_store(struct btrfs_lru_cache *cache,
                          struct btrfs_lru_cache_entry *new_entry,
                          gfp_t gfp);
void btrfs_lru_cache_remove(struct btrfs_lru_cache *cache,
                            struct btrfs_lru_cache_entry *entry);
void btrfs_lru_cache_clear(struct btrfs_lru_cache *cache);

#endif