/*
   * Copyright (C) 2001 Momchil Velikov
   * Portions Copyright (C) 2001 Christoph Hellwig
   * Copyright (C) 2006 Nick Piggin
   * Copyright (C) 2012 Konstantin Khlebnikov
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License as
   * published by the Free Software Foundation; either version 2, or (at
   * your option) any later version.
   * 
   * This program is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   * 
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
   */
  #ifndef _LINUX_RADIX_TREE_H
  #define _LINUX_RADIX_TREE_H
  
  #include <linux/preempt.h>
  #include <linux/types.h>
  #include <linux/bug.h>
  #include <linux/kernel.h>
  #include <linux/rcupdate.h>
  
  /*
   * An indirect pointer (root->rnode pointing to a radix_tree_node, rather
   * than a data item) is signalled by the low bit set in the root->rnode
   * pointer.
   *
   * In this case root->height is > 0, but the indirect pointer tests are
   * needed for RCU lookups (because root->height is unreliable). The only
   * time callers need worry about this is when doing a lookup_slot under
   * RCU.
   *
   * Indirect pointer in fact is also used to tag the last pointer of a node
   * when it is shrunk, before we rcu free the node. See shrink code for
   * details.
   */
  #define RADIX_TREE_INDIRECT_PTR		1
  /*
   * A common use of the radix tree is to store pointers to struct pages;
   * but shmem/tmpfs needs also to store swap entries in the same tree:
   * those are marked as exceptional entries to distinguish them.
   * EXCEPTIONAL_ENTRY tests the bit, EXCEPTIONAL_SHIFT shifts content past it.
   */
  #define RADIX_TREE_EXCEPTIONAL_ENTRY	2
  #define RADIX_TREE_EXCEPTIONAL_SHIFT	2
  
  static inline int radix_tree_is_indirect_ptr(void *ptr)
  {
  	return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
  }
  
  /*** radix-tree API starts here ***/
  
  #define RADIX_TREE_MAX_TAGS 3
  
  /* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
  struct radix_tree_root {
  	unsigned int		height;
  	gfp_t			gfp_mask;
  	struct radix_tree_node	__rcu *rnode;
  };
  
  #define RADIX_TREE_INIT(mask)	{					\
  	.height = 0,							\
  	.gfp_mask = (mask),						\
  	.rnode = NULL,							\
  }
  
  #define RADIX_TREE(name, mask) \
  	struct radix_tree_root name = RADIX_TREE_INIT(mask)
  
  #define INIT_RADIX_TREE(root, mask)					\
  do {									\
  	(root)->height = 0;						\
  	(root)->gfp_mask = (mask);					\
  	(root)->rnode = NULL;						\
  } while (0)
  
  /**
   * Radix-tree synchronization
   *
   * The radix-tree API requires that users provide all synchronisation (with
   * specific exceptions, noted below).
   *
   * Synchronization of access to the data items being stored in the tree, and
   * management of their lifetimes must be completely managed by API users.
   *
   * For API usage, in general,
   * - any function _modifying_ the tree or tags (inserting or deleting
   *   items, setting or clearing tags) must exclude other modifications, and
   *   exclude any functions reading the tree.
   * - any function _reading_ the tree or tags (looking up items or tags,
   *   gang lookups) must exclude modifications to the tree, but may occur
   *   concurrently with other readers.
   *
   * The notable exceptions to this rule are the following functions:
   * radix_tree_lookup
   * radix_tree_lookup_slot
   * radix_tree_tag_get
   * radix_tree_gang_lookup
   * radix_tree_gang_lookup_slot
   * radix_tree_gang_lookup_tag
   * radix_tree_gang_lookup_tag_slot
   * radix_tree_tagged
   *
   * The first 7 functions are able to be called locklessly, using RCU. The
   * caller must ensure calls to these functions are made within rcu_read_lock()
   * regions. Other readers (lock-free or otherwise) and modifications may be
   * running concurrently.
   *
   * It is still required that the caller manage the synchronization and lifetimes
   * of the items. So if RCU lock-free lookups are used, typically this would mean
   * that the items have their own locks, or are amenable to lock-free access; and
   * that the items are freed by RCU (or only freed after having been deleted from
   * the radix tree *and* a synchronize_rcu() grace period).
   *
   * (Note, rcu_assign_pointer and rcu_dereference are not needed to control
   * access to data items when inserting into or looking up from the radix tree)
   *
   * Note that the value returned by radix_tree_tag_get() may not be relied upon
   * if only the RCU read lock is held.  Functions to set/clear tags and to
   * delete nodes running concurrently with it may affect its result such that
   * two consecutive reads in the same locked section may return different
   * values.  If reliability is required, modification functions must also be
   * excluded from concurrency.
   *
   * radix_tree_tagged is able to be called without locking or RCU.
   */
  
  /**
   * radix_tree_deref_slot	- dereference a slot
   * @pslot:	pointer to slot, returned by radix_tree_lookup_slot
   * Returns:	item that was stored in that slot with any direct pointer flag
   *		removed.
   *
   * For use with radix_tree_lookup_slot().  Caller must hold tree at least read
   * locked across slot lookup and dereference. Not required if write lock is
   * held (ie. items cannot be concurrently inserted).
   *
   * radix_tree_deref_retry must be used to confirm validity of the pointer if
   * only the read lock is held.
   */
  static inline void *radix_tree_deref_slot(void **pslot)
  {
  	return rcu_dereference(*pslot);
  }
  
  /**
   * radix_tree_deref_slot_protected	- dereference a slot without RCU lock but with tree lock held
   * @pslot:	pointer to slot, returned by radix_tree_lookup_slot
   * Returns:	item that was stored in that slot with any direct pointer flag
   *		removed.
   *
   * Similar to radix_tree_deref_slot but only used during migration when a pages
   * mapping is being moved. The caller does not hold the RCU read lock but it
   * must hold the tree lock to prevent parallel updates.
   */
  static inline void *radix_tree_deref_slot_protected(void **pslot,
  							spinlock_t *treelock)
  {
  	return rcu_dereference_protected(*pslot, lockdep_is_held(treelock));
  }
  
  /**
   * radix_tree_deref_retry	- check radix_tree_deref_slot
   * @arg:	pointer returned by radix_tree_deref_slot
   * Returns:	0 if retry is not required, otherwise retry is required
   *
   * radix_tree_deref_retry must be used with radix_tree_deref_slot.
   */
  static inline int radix_tree_deref_retry(void *arg)
  {
  	return unlikely((unsigned long)arg & RADIX_TREE_INDIRECT_PTR);
  }
  
  /**
   * radix_tree_exceptional_entry	- radix_tree_deref_slot gave exceptional entry?
   * @arg:	value returned by radix_tree_deref_slot
   * Returns:	0 if well-aligned pointer, non-0 if exceptional entry.
   */
  static inline int radix_tree_exceptional_entry(void *arg)
  {
  	/* Not unlikely because radix_tree_exception often tested first */
  	return (unsigned long)arg & RADIX_TREE_EXCEPTIONAL_ENTRY;
  }
  
  /**
   * radix_tree_exception	- radix_tree_deref_slot returned either exception?
   * @arg:	value returned by radix_tree_deref_slot
   * Returns:	0 if well-aligned pointer, non-0 if either kind of exception.
   */
  static inline int radix_tree_exception(void *arg)
  {
  	return unlikely((unsigned long)arg &
  		(RADIX_TREE_INDIRECT_PTR | RADIX_TREE_EXCEPTIONAL_ENTRY));
  }
  
  /**
   * radix_tree_replace_slot	- replace item in a slot
   * @pslot:	pointer to slot, returned by radix_tree_lookup_slot
   * @item:	new item to store in the slot.
   *
   * For use with radix_tree_lookup_slot().  Caller must hold tree write locked
   * across slot lookup and replacement.
   */
  static inline void radix_tree_replace_slot(void **pslot, void *item)
  {
  	BUG_ON(radix_tree_is_indirect_ptr(item));
  	rcu_assign_pointer(*pslot, item);
  }
  
  int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
  void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
  void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
  void *radix_tree_delete_item(struct radix_tree_root *, unsigned long, void *);
  void *radix_tree_delete(struct radix_tree_root *, unsigned long);
  unsigned int
  radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
  			unsigned long first_index, unsigned int max_items);
  unsigned int radix_tree_gang_lookup_slot(struct radix_tree_root *root,
  			void ***results, unsigned long *indices,
  			unsigned long first_index, unsigned int max_items);
  int radix_tree_preload(gfp_t gfp_mask);
  int radix_tree_maybe_preload(gfp_t gfp_mask);
  void radix_tree_init(void);
  void *radix_tree_tag_set(struct radix_tree_root *root,
  			unsigned long index, unsigned int tag);
  void *radix_tree_tag_clear(struct radix_tree_root *root,
  			unsigned long index, unsigned int tag);
  int radix_tree_tag_get(struct radix_tree_root *root,
  			unsigned long index, unsigned int tag);
  unsigned int
  radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
  		unsigned long first_index, unsigned int max_items,
  		unsigned int tag);
  unsigned int
  radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
  		unsigned long first_index, unsigned int max_items,
  		unsigned int tag);
  unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
  		unsigned long *first_indexp, unsigned long last_index,
  		unsigned long nr_to_tag,
  		unsigned int fromtag, unsigned int totag);
  int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);
  unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item);
  
  static inline void radix_tree_preload_end(void)
  {
  	preempt_enable();
  }
  
  /**
   * struct radix_tree_iter - radix tree iterator state
   *
   * @index:	index of current slot
   * @next_index:	next-to-last index for this chunk
   * @tags:	bit-mask for tag-iterating
   *
   * This radix tree iterator works in terms of "chunks" of slots.  A chunk is a
   * subinterval of slots contained within one radix tree leaf node.  It is
   * described by a pointer to its first slot and a struct radix_tree_iter
   * which holds the chunk's position in the tree and its size.  For tagged
   * iteration radix_tree_iter also holds the slots' bit-mask for one chosen
   * radix tree tag.
   */
  struct radix_tree_iter {
  	unsigned long	index;
  	unsigned long	next_index;
  	unsigned long	tags;
  };
  
  #define RADIX_TREE_ITER_TAG_MASK	0x00FF	/* tag index in lower byte */
  #define RADIX_TREE_ITER_TAGGED		0x0100	/* lookup tagged slots */
  #define RADIX_TREE_ITER_CONTIG		0x0200	/* stop at first hole */
  
  /**
   * radix_tree_iter_init - initialize radix tree iterator
   *
   * @iter:	pointer to iterator state
   * @start:	iteration starting index
   * Returns:	NULL
   */
  static __always_inline void **
  radix_tree_iter_init(struct radix_tree_iter *iter, unsigned long start)
  {
  	/*
  	 * Leave iter->tags uninitialized. radix_tree_next_chunk() will fill it
  	 * in the case of a successful tagged chunk lookup.  If the lookup was
  	 * unsuccessful or non-tagged then nobody cares about ->tags.
  	 *
  	 * Set index to zero to bypass next_index overflow protection.
  	 * See the comment in radix_tree_next_chunk() for details.
  	 */
  	iter->index = 0;
  	iter->next_index = start;
  	return NULL;
  }
  
  /**
   * radix_tree_next_chunk - find next chunk of slots for iteration
   *
   * @root:	radix tree root
   * @iter:	iterator state
   * @flags:	RADIX_TREE_ITER_* flags and tag index
   * Returns:	pointer to chunk first slot, or NULL if there no more left
   *
   * This function looks up the next chunk in the radix tree starting from
   * @iter->next_index.  It returns a pointer to the chunk's first slot.
   * Also it fills @iter with data about chunk: position in the tree (index),
   * its end (next_index), and constructs a bit mask for tagged iterating (tags).
   */
  void **radix_tree_next_chunk(struct radix_tree_root *root,
  			     struct radix_tree_iter *iter, unsigned flags);
  
  /**
   * radix_tree_chunk_size - get current chunk size
   *
   * @iter:	pointer to radix tree iterator
   * Returns:	current chunk size
   */
  static __always_inline unsigned
  radix_tree_chunk_size(struct radix_tree_iter *iter)
  {
  	return iter->next_index - iter->index;
  }
  
  /**
   * radix_tree_next_slot - find next slot in chunk
   *
   * @slot:	pointer to current slot
   * @iter:	pointer to interator state
   * @flags:	RADIX_TREE_ITER_*, should be constant
   * Returns:	pointer to next slot, or NULL if there no more left
   *
   * This function updates @iter->index in the case of a successful lookup.
   * For tagged lookup it also eats @iter->tags.
   */
  static __always_inline void **
  radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
  {
  	if (flags & RADIX_TREE_ITER_TAGGED) {
  		iter->tags >>= 1;
  		if (likely(iter->tags & 1ul)) {
  			iter->index++;
  			return slot + 1;
  		}
  		if (!(flags & RADIX_TREE_ITER_CONTIG) && likely(iter->tags)) {
  			unsigned offset = __ffs(iter->tags);
  
  			iter->tags >>= offset;
  			iter->index += offset + 1;
  			return slot + offset + 1;
  		}
  	} else {
  		unsigned size = radix_tree_chunk_size(iter) - 1;
  
  		while (size--) {
  			slot++;
  			iter->index++;
  			if (likely(*slot))
  				return slot;
  			if (flags & RADIX_TREE_ITER_CONTIG) {
  				/* forbid switching to the next chunk */
  				iter->next_index = 0;
  				break;
  			}
  		}
  	}
  	return NULL;
  }
  
  /**
   * radix_tree_for_each_chunk - iterate over chunks
   *
   * @slot:	the void** variable for pointer to chunk first slot
   * @root:	the struct radix_tree_root pointer
   * @iter:	the struct radix_tree_iter pointer
   * @start:	iteration starting index
   * @flags:	RADIX_TREE_ITER_* and tag index
   *
   * Locks can be released and reacquired between iterations.
   */
  #define radix_tree_for_each_chunk(slot, root, iter, start, flags)	\
  	for (slot = radix_tree_iter_init(iter, start) ;			\
  	      (slot = radix_tree_next_chunk(root, iter, flags)) ;)
  
  /**
   * radix_tree_for_each_chunk_slot - iterate over slots in one chunk
   *
   * @slot:	the void** variable, at the beginning points to chunk first slot
   * @iter:	the struct radix_tree_iter pointer
   * @flags:	RADIX_TREE_ITER_*, should be constant
   *
   * This macro is designed to be nested inside radix_tree_for_each_chunk().
   * @slot points to the radix tree slot, @iter->index contains its index.
   */
  #define radix_tree_for_each_chunk_slot(slot, iter, flags)		\
  	for (; slot ; slot = radix_tree_next_slot(slot, iter, flags))
  
  /**
   * radix_tree_for_each_slot - iterate over non-empty slots
   *
   * @slot:	the void** variable for pointer to slot
   * @root:	the struct radix_tree_root pointer
   * @iter:	the struct radix_tree_iter pointer
   * @start:	iteration starting index
   *
   * @slot points to radix tree slot, @iter->index contains its index.
   */
  #define radix_tree_for_each_slot(slot, root, iter, start)		\
  	for (slot = radix_tree_iter_init(iter, start) ;			\
  	     slot || (slot = radix_tree_next_chunk(root, iter, 0)) ;	\
  	     slot = radix_tree_next_slot(slot, iter, 0))
  
  /**
   * radix_tree_for_each_contig - iterate over contiguous slots
   *
   * @slot:	the void** variable for pointer to slot
   * @root:	the struct radix_tree_root pointer
   * @iter:	the struct radix_tree_iter pointer
   * @start:	iteration starting index
   *
   * @slot points to radix tree slot, @iter->index contains its index.
   */
  #define radix_tree_for_each_contig(slot, root, iter, start)		\
  	for (slot = radix_tree_iter_init(iter, start) ;			\
  	     slot || (slot = radix_tree_next_chunk(root, iter,		\
  				RADIX_TREE_ITER_CONTIG)) ;		\
  	     slot = radix_tree_next_slot(slot, iter,			\
  				RADIX_TREE_ITER_CONTIG))
  
  /**
   * radix_tree_for_each_tagged - iterate over tagged slots
   *
   * @slot:	the void** variable for pointer to slot
   * @root:	the struct radix_tree_root pointer
   * @iter:	the struct radix_tree_iter pointer
   * @start:	iteration starting index
   * @tag:	tag index
   *
   * @slot points to radix tree slot, @iter->index contains its index.
   */
  #define radix_tree_for_each_tagged(slot, root, iter, start, tag)	\
  	for (slot = radix_tree_iter_init(iter, start) ;			\
  	     slot || (slot = radix_tree_next_chunk(root, iter,		\
  			      RADIX_TREE_ITER_TAGGED | tag)) ;		\
  	     slot = radix_tree_next_slot(slot, iter,			\
  				RADIX_TREE_ITER_TAGGED))
  
  #endif /* _LINUX_RADIX_TREE_H */