/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
 * Copyright (C) 2008 Red Hat, Inc. All rights reserved.
 *
 * Device-mapper snapshot exception store.
 *
 * This file is released under the GPL.
 */

#ifndef _LINUX_DM_EXCEPTION_STORE
#define _LINUX_DM_EXCEPTION_STORE

#include <linux/blkdev.h>
#include <linux/list_bl.h>
#include <linux/device-mapper.h>

/*
 * The snapshot code deals with largish chunks of the disk at a
 * time. Typically 32k - 512k.
 */
typedef sector_t chunk_t;

/*
 * An exception is used where an old chunk of data has been
 * replaced by a new one.
 * If chunk_t is 64 bits in size, the top 8 bits of new_chunk hold the number
 * of chunks that follow contiguously.  Remaining bits hold the number of the
 * chunk within the device.
 */
struct dm_exception {
        struct hlist_node hash_list;

        chunk_t old_chunk;
        chunk_t new_chunk;
};

/*
 * Abstraction to handle the meta/layout of exception stores (the
 * COW device).
 */
struct dm_exception_store;
struct dm_exception_store_type {
        const char *name;
        struct module *module;

        int (*ctr)(struct dm_exception_store *store, char *options);

        /*
         * Destroys this object when you've finished with it.
         */
        void (*dtr)(struct dm_exception_store *store);

        /*
         * The target shouldn't read the COW device until this is
         * called.  As exceptions are read from the COW, they are
         * reported back via the callback.
         */
        int (*read_metadata)(struct dm_exception_store *store,
                             int (*callback)(void *callback_context,
                                             chunk_t old, chunk_t new),
                             void *callback_context);

        /*
         * Find somewhere to store the next exception.
         */
        int (*prepare_exception)(struct dm_exception_store *store,
                                 struct dm_exception *e);

        /*
         * Update the metadata with this exception.
         */
        void (*commit_exception)(struct dm_exception_store *store,
                                 struct dm_exception *e, int valid,
                                 void (*callback)(void *, int success),
                                 void *callback_context);

        /*
         * Returns 0 if the exception store is empty.
         *
         * If there are exceptions still to be merged, sets
         * *last_old_chunk and *last_new_chunk to the most recent
         * still-to-be-merged chunk and returns the number of
         * consecutive previous ones.
         */
        int (*prepare_merge)(struct dm_exception_store *store,
                             chunk_t *last_old_chunk, chunk_t *last_new_chunk);

        /*
         * Clear the last n exceptions.
         * nr_merged must be <= the value returned by prepare_merge.
         */
        int (*commit_merge)(struct dm_exception_store *store, int nr_merged);

        /*
         * The snapshot is invalid, note this in the metadata.
         */
        void (*drop_snapshot)(struct dm_exception_store *store);

        unsigned int (*status)(struct dm_exception_store *store,
                               status_type_t status, char *result,
                               unsigned int maxlen);

        /*
         * Return how full the snapshot is.
         */
        void (*usage)(struct dm_exception_store *store,
                      sector_t *total_sectors, sector_t *sectors_allocated,
                      sector_t *metadata_sectors);

        /* For internal device-mapper use only. */
        struct list_head list;
};

struct dm_snapshot;

struct dm_exception_store {
        struct dm_exception_store_type *type;
        struct dm_snapshot *snap;

        /* Size of data blocks saved - must be a power of 2 */
        unsigned int chunk_size;
        unsigned int chunk_mask;
        unsigned int chunk_shift;

        void *context;

        bool userspace_supports_overflow;
};

/*
 * Obtain the origin or cow device used by a given snapshot.
 */
struct dm_dev *dm_snap_origin(struct dm_snapshot *snap);
struct dm_dev *dm_snap_cow(struct dm_snapshot *snap);

/*
 * Funtions to manipulate consecutive chunks
 */
#define DM_CHUNK_CONSECUTIVE_BITS 8
#define DM_CHUNK_NUMBER_BITS 56

static inline chunk_t dm_chunk_number(chunk_t chunk)
{
        return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL);
}

static inline unsigned int dm_consecutive_chunk_count(struct dm_exception *e)
{
        return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
}

static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
{
        e->new_chunk += (1ULL << DM_CHUNK_NUMBER_BITS);

        BUG_ON(!dm_consecutive_chunk_count(e));
}

static inline void dm_consecutive_chunk_count_dec(struct dm_exception *e)
{
        BUG_ON(!dm_consecutive_chunk_count(e));

        e->new_chunk -= (1ULL << DM_CHUNK_NUMBER_BITS);
}

/*
 * Return the number of sectors in the device.
 */
static inline sector_t get_dev_size(struct block_device *bdev)
{
        return bdev_nr_sectors(bdev);
}

static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
                                      sector_t sector)
{
        return sector >> store->chunk_shift;
}

int dm_exception_store_type_register(struct dm_exception_store_type *type);
int dm_exception_store_type_unregister(struct dm_exception_store_type *type);

int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
                                      unsigned int chunk_size,
                                      char **error);

int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
                              struct dm_snapshot *snap,
                              unsigned int *args_used,
                              struct dm_exception_store **store);
void dm_exception_store_destroy(struct dm_exception_store *store);

int dm_exception_store_init(void);
void dm_exception_store_exit(void);

/*
 * Two exception store implementations.
 */
int dm_persistent_snapshot_init(void);
void dm_persistent_snapshot_exit(void);

int dm_transient_snapshot_init(void);
void dm_transient_snapshot_exit(void);

#endif /* _LINUX_DM_EXCEPTION_STORE */