/*
   * 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 */