#ifndef BTREE_H
  #define BTREE_H
  
  #include <linux/kernel.h>
  #include <linux/mempool.h>
  
  /**
   * DOC: B+Tree basics
   *
   * A B+Tree is a data structure for looking up arbitrary (currently allowing
   * unsigned long, u32, u64 and 2 * u64) keys into pointers. The data structure
   * is described at http://en.wikipedia.org/wiki/B-tree, we currently do not
   * use binary search to find the key on lookups.
   *
   * Each B+Tree consists of a head, that contains bookkeeping information and
   * a variable number (starting with zero) nodes. Each node contains the keys
   * and pointers to sub-nodes, or, for leaf nodes, the keys and values for the
   * tree entries.
   *
   * Each node in this implementation has the following layout:
   * [key1, key2, ..., keyN] [val1, val2, ..., valN]
   *
   * Each key here is an array of unsigned longs, geo->no_longs in total. The
   * number of keys and values (N) is geo->no_pairs.
   */
  
  /**
   * struct btree_head - btree head
   *
   * @node: the first node in the tree
   * @mempool: mempool used for node allocations
   * @height: current of the tree
   */
  struct btree_head {
  	unsigned long *node;
  	mempool_t *mempool;
  	int height;
  };
  
  /* btree geometry */
  struct btree_geo;
  
  /**
   * btree_alloc - allocate function for the mempool
   * @gfp_mask: gfp mask for the allocation
   * @pool_data: unused
   */
  void *btree_alloc(gfp_t gfp_mask, void *pool_data);
  
  /**
   * btree_free - free function for the mempool
   * @element: the element to free
   * @pool_data: unused
   */
  void btree_free(void *element, void *pool_data);
  
  /**
   * btree_init_mempool - initialise a btree with given mempool
   *
   * @head: the btree head to initialise
   * @mempool: the mempool to use
   *
   * When this function is used, there is no need to destroy
   * the mempool.
   */
  void btree_init_mempool(struct btree_head *head, mempool_t *mempool);
  
  /**
   * btree_init - initialise a btree
   *
   * @head: the btree head to initialise
   *
   * This function allocates the memory pool that the
   * btree needs. Returns zero or a negative error code
   * (-%ENOMEM) when memory allocation fails.
   *
   */
  int __must_check btree_init(struct btree_head *head);
  
  /**
   * btree_destroy - destroy mempool
   *
   * @head: the btree head to destroy
   *
   * This function destroys the internal memory pool, use only
   * when using btree_init(), not with btree_init_mempool().
   */
  void btree_destroy(struct btree_head *head);
  
  /**
   * btree_lookup - look up a key in the btree
   *
   * @head: the btree to look in
   * @geo: the btree geometry
   * @key: the key to look up
   *
   * This function returns the value for the given key, or %NULL.
   */
  void *btree_lookup(struct btree_head *head, struct btree_geo *geo,
  		   unsigned long *key);
  
  /**
   * btree_insert - insert an entry into the btree
   *
   * @head: the btree to add to
   * @geo: the btree geometry
   * @key: the key to add (must not already be present)
   * @val: the value to add (must not be %NULL)
   * @gfp: allocation flags for node allocations
   *
   * This function returns 0 if the item could be added, or an
   * error code if it failed (may fail due to memory pressure).
   */
  int __must_check btree_insert(struct btree_head *head, struct btree_geo *geo,
  			      unsigned long *key, void *val, gfp_t gfp);
  /**
   * btree_update - update an entry in the btree
   *
   * @head: the btree to update
   * @geo: the btree geometry
   * @key: the key to update
   * @val: the value to change it to (must not be %NULL)
   *
   * This function returns 0 if the update was successful, or
   * -%ENOENT if the key could not be found.
   */
  int btree_update(struct btree_head *head, struct btree_geo *geo,
  		 unsigned long *key, void *val);
  /**
   * btree_remove - remove an entry from the btree
   *
   * @head: the btree to update
   * @geo: the btree geometry
   * @key: the key to remove
   *
   * This function returns the removed entry, or %NULL if the key
   * could not be found.
   */
  void *btree_remove(struct btree_head *head, struct btree_geo *geo,
  		   unsigned long *key);
  
  /**
   * btree_merge - merge two btrees
   *
   * @target: the tree that gets all the entries
   * @victim: the tree that gets merged into @target
   * @geo: the btree geometry
   * @gfp: allocation flags
   *
   * The two trees @target and @victim may not contain the same keys,
   * that is a bug and triggers a BUG(). This function returns zero
   * if the trees were merged successfully, and may return a failure
   * when memory allocation fails, in which case both trees might have
   * been partially merged, i.e. some entries have been moved from
   * @victim to @target.
   */
  int btree_merge(struct btree_head *target, struct btree_head *victim,
  		struct btree_geo *geo, gfp_t gfp);
  
  /**
   * btree_last - get last entry in btree
   *
   * @head: btree head
   * @geo: btree geometry
   * @key: last key
   *
   * Returns the last entry in the btree, and sets @key to the key
   * of that entry; returns NULL if the tree is empty, in that case
   * key is not changed.
   */
  void *btree_last(struct btree_head *head, struct btree_geo *geo,
  		 unsigned long *key);
  
  /**
   * btree_get_prev - get previous entry
   *
   * @head: btree head
   * @geo: btree geometry
   * @key: pointer to key
   *
   * The function returns the next item right before the value pointed to by
   * @key, and updates @key with its key, or returns %NULL when there is no
   * entry with a key smaller than the given key.
   */
  void *btree_get_prev(struct btree_head *head, struct btree_geo *geo,
  		     unsigned long *key);
  
  
  /* internal use, use btree_visitor{l,32,64,128} */
  size_t btree_visitor(struct btree_head *head, struct btree_geo *geo,
  		     unsigned long opaque,
  		     void (*func)(void *elem, unsigned long opaque,
  				  unsigned long *key, size_t index,
  				  void *func2),
  		     void *func2);
  
  /* internal use, use btree_grim_visitor{l,32,64,128} */
  size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo,
  			  unsigned long opaque,
  			  void (*func)(void *elem, unsigned long opaque,
  				       unsigned long *key,
  				       size_t index, void *func2),
  			  void *func2);
  
  
  #include <linux/btree-128.h>
  
  extern struct btree_geo btree_geo32;
  #define BTREE_TYPE_SUFFIX l
  #define BTREE_TYPE_BITS BITS_PER_LONG
  #define BTREE_TYPE_GEO &btree_geo32
  #define BTREE_KEYTYPE unsigned long
  #include <linux/btree-type.h>
  
  #define btree_for_each_safel(head, key, val)	\
  	for (val = btree_lastl(head, &key);	\
  	     val;				\
  	     val = btree_get_prevl(head, &key))
  
  #define BTREE_TYPE_SUFFIX 32
  #define BTREE_TYPE_BITS 32
  #define BTREE_TYPE_GEO &btree_geo32
  #define BTREE_KEYTYPE u32
  #include <linux/btree-type.h>
  
  #define btree_for_each_safe32(head, key, val)	\
  	for (val = btree_last32(head, &key);	\
  	     val;				\
  	     val = btree_get_prev32(head, &key))
  
  extern struct btree_geo btree_geo64;
  #define BTREE_TYPE_SUFFIX 64
  #define BTREE_TYPE_BITS 64
  #define BTREE_TYPE_GEO &btree_geo64
  #define BTREE_KEYTYPE u64
  #include <linux/btree-type.h>
  
  #define btree_for_each_safe64(head, key, val)	\
  	for (val = btree_last64(head, &key);	\
  	     val;				\
  	     val = btree_get_prev64(head, &key))
  
  #endif