dm-exception-store.h

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/*
 * 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/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 list_head 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,
            unsigned argc, char **argv);

    /*
     * 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,
                  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 (*status) (struct dm_exception_store *store,
                status_type_t status, char *result,
                unsigned 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 chunk_size;
    unsigned chunk_mask;
    unsigned chunk_shift;

    void *context;
};

/*
 * 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
 */
#  if defined(CONFIG_LBDAF) || (BITS_PER_LONG == 64)
#    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 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);
}

#  else
#    define DM_CHUNK_CONSECUTIVE_BITS 0

static inline chunk_t dm_chunk_number(chunk_t chunk)
{
    return chunk;
}

static inline unsigned dm_consecutive_chunk_count(struct dm_exception *e)
{
    return 0;
}

static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
{
}

static inline void dm_consecutive_chunk_count_dec(struct dm_exception *e)
{
}

#  endif

/*
 * Return the number of sectors in the device.
 */
static inline sector_t get_dev_size(struct block_device *bdev)
{
    return i_size_read(bdev->bd_inode) >> SECTOR_SHIFT;
}

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 chunk_size,
                      char **error);

int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
                  struct dm_snapshot *snap,
                  unsigned *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 */