/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * Copyright (C) 2012 Red Hat. All rights reserved.
 *
 * This file is released under the GPL.
 */

#ifndef DM_CACHE_POLICY_H
#define DM_CACHE_POLICY_H

#include "dm-cache-block-types.h"

#include <linux/device-mapper.h>

/*----------------------------------------------------------------*/

/*
 * The cache policy makes the important decisions about which blocks get to
 * live on the faster cache device.
 */
enum policy_operation {
        POLICY_PROMOTE,
        POLICY_DEMOTE,
        POLICY_WRITEBACK
};

/*
 * This is the instruction passed back to the core target.
 */
struct policy_work {
        enum policy_operation op;
        dm_oblock_t oblock;
        dm_cblock_t cblock;
};

/*
 * The cache policy object.  It is envisaged that this structure will be
 * embedded in a bigger, policy specific structure (ie. use container_of()).
 */
struct dm_cache_policy {
        /*
         * Destroys this object.
         */
        void (*destroy)(struct dm_cache_policy *p);

        /*
         * Find the location of a block.
         *
         * Must not block.
         *
         * Returns 0 if in cache (cblock will be set), -ENOENT if not, < 0 for
         * other errors (-EWOULDBLOCK would be typical).  data_dir should be
         * READ or WRITE. fast_copy should be set if migrating this block would
         * be 'cheap' somehow (eg, discarded data). background_queued will be set
         * if a migration has just been queued.
         */
        int (*lookup)(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock,
                      int data_dir, bool fast_copy, bool *background_queued);

        /*
         * Sometimes the core target can optimise a migration, eg, the
         * block may be discarded, or the bio may cover an entire block.
         * In order to optimise it needs the migration immediately though
         * so it knows to do something different with the bio.
         *
         * This method is optional (policy-internal will fallback to using
         * lookup).
         */
        int (*lookup_with_work)(struct dm_cache_policy *p,
                                dm_oblock_t oblock, dm_cblock_t *cblock,
                                int data_dir, bool fast_copy,
                                struct policy_work **work);

        /*
         * Retrieves background work.  Returns -ENODATA when there's no
         * background work.
         */
        int (*get_background_work)(struct dm_cache_policy *p, bool idle,
                                   struct policy_work **result);

        /*
         * You must pass in the same work pointer that you were given, not
         * a copy.
         */
        void (*complete_background_work)(struct dm_cache_policy *p,
                                         struct policy_work *work,
                                         bool success);

        void (*set_dirty)(struct dm_cache_policy *p, dm_cblock_t cblock);
        void (*clear_dirty)(struct dm_cache_policy *p, dm_cblock_t cblock);

        /*
         * Called when a cache target is first created.  Used to load a
         * mapping from the metadata device into the policy.
         */
        int (*load_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock,
                            dm_cblock_t cblock, bool dirty,
                            uint32_t hint, bool hint_valid);

        /*
         * Drops the mapping, irrespective of whether it's clean or dirty.
         * Returns -ENODATA if cblock is not mapped.
         */
        int (*invalidate_mapping)(struct dm_cache_policy *p, dm_cblock_t cblock);

        /*
         * Gets the hint for a given cblock.  Called in a single threaded
         * context.  So no locking required.
         */
        uint32_t (*get_hint)(struct dm_cache_policy *p, dm_cblock_t cblock);

        /*
         * How full is the cache?
         */
        dm_cblock_t (*residency)(struct dm_cache_policy *p);

        /*
         * Because of where we sit in the block layer, we can be asked to
         * map a lot of little bios that are all in the same block (no
         * queue merging has occurred).  To stop the policy being fooled by
         * these, the core target sends regular tick() calls to the policy.
         * The policy should only count an entry as hit once per tick.
         *
         * This method is optional.
         */
        void (*tick)(struct dm_cache_policy *p, bool can_block);

        /*
         * Configuration.
         */
        int (*emit_config_values)(struct dm_cache_policy *p, char *result,
                                  unsigned int maxlen, ssize_t *sz_ptr);
        int (*set_config_value)(struct dm_cache_policy *p,
                                const char *key, const char *value);

        void (*allow_migrations)(struct dm_cache_policy *p, bool allow);

        /*
         * Book keeping ptr for the policy register, not for general use.
         */
        void *private;
};

/*----------------------------------------------------------------*/

/*
 * We maintain a little register of the different policy types.
 */
#define CACHE_POLICY_NAME_SIZE 16
#define CACHE_POLICY_VERSION_SIZE 3

struct dm_cache_policy_type {
        /* For use by the register code only. */
        struct list_head list;

        /*
         * Policy writers should fill in these fields.  The name field is
         * what gets passed on the target line to select your policy.
         */
        char name[CACHE_POLICY_NAME_SIZE];
        unsigned int version[CACHE_POLICY_VERSION_SIZE];

        /*
         * For use by an alias dm_cache_policy_type to point to the
         * real dm_cache_policy_type.
         */
        struct dm_cache_policy_type *real;

        /*
         * Policies may store a hint for each cache block.
         * Currently the size of this hint must be 0 or 4 bytes but we
         * expect to relax this in future.
         */
        size_t hint_size;

        struct module *owner;
        struct dm_cache_policy *(*create)(dm_cblock_t cache_size,
                                          sector_t origin_size,
                                          sector_t block_size);
};

int dm_cache_policy_register(struct dm_cache_policy_type *type);
void dm_cache_policy_unregister(struct dm_cache_policy_type *type);

/*----------------------------------------------------------------*/

#endif  /* DM_CACHE_POLICY_H */