include/linux/radix-tree.h

   1 /*
   2  * Copyright (C) 2001 Momchil Velikov
   3  * Portions Copyright (C) 2001 Christoph Hellwig
   4  * Copyright (C) 2006 Nick Piggin
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License as
   8  * published by the Free Software Foundation; either version 2, or (at
   9  * your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful, but
  12  * WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19  */
  20 #ifndef _LINUX_RADIX_TREE_H
  21 #define _LINUX_RADIX_TREE_H
  22
  23 #include <linux/preempt.h>
  24 #include <linux/types.h>
  25 #include <linux/kernel.h>
  26 #include <linux/rcupdate.h>
  27
  28 /*
  29  * A direct pointer (root->rnode pointing directly to a data item,
  30  * rather than another radix_tree_node) is signalled by the low bit
  31  * set in the root->rnode pointer.
  32  *
  33  * In this case root->height is also NULL, but the direct pointer tests are
  34  * needed for RCU lookups when root->height is unreliable.
  35  */
  36 #define RADIX_TREE_DIRECT_PTR   1
  37
  38 static inline void *radix_tree_ptr_to_direct(void *ptr)
  39 {
  40         return (void *)((unsigned long)ptr | RADIX_TREE_DIRECT_PTR);
  41 }
  42
  43 static inline void *radix_tree_direct_to_ptr(void *ptr)
  44 {
  45         return (void *)((unsigned long)ptr & ~RADIX_TREE_DIRECT_PTR);
  46 }
  47
  48 static inline int radix_tree_is_direct_ptr(void *ptr)
  49 {
  50         return (int)((unsigned long)ptr & RADIX_TREE_DIRECT_PTR);
  51 }
  52
  53 /*** radix-tree API starts here ***/
  54
  55 #define RADIX_TREE_MAX_TAGS 2
  56
  57 /* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
  58 struct radix_tree_root {
  59         unsigned int            height;
  60         gfp_t                   gfp_mask;
  61         struct radix_tree_node  *rnode;
  62 };
  63
  64 #define RADIX_TREE_INIT(mask)   {                                       \
  65         .height = 0,                                                    \
  66         .gfp_mask = (mask),                                             \
  67         .rnode = NULL,                                                  \
  68 }
  69
  70 #define RADIX_TREE(name, mask) \
  71         struct radix_tree_root name = RADIX_TREE_INIT(mask)
  72
  73 #define INIT_RADIX_TREE(root, mask)                                     \
  74 do {                                                                    \
  75         (root)->height = 0;                                             \
  76         (root)->gfp_mask = (mask);                                      \
  77         (root)->rnode = NULL;                                           \
  78 } while (0)
  79
  80 /**
  81  * Radix-tree synchronization
  82  *
  83  * The radix-tree API requires that users provide all synchronisation (with
  84  * specific exceptions, noted below).
  85  *
  86  * Synchronization of access to the data items being stored in the tree, and
  87  * management of their lifetimes must be completely managed by API users.
  88  *
  89  * For API usage, in general,
  90  * - any function _modifying_ the tree or tags (inserting or deleting
  91  *   items, setting or clearing tags must exclude other modifications, and
  92  *   exclude any functions reading the tree.
  93  * - any function _reading_ the tree or tags (looking up items or tags,
  94  *   gang lookups) must exclude modifications to the tree, but may occur
  95  *   concurrently with other readers.
  96  *
  97  * The notable exceptions to this rule are the following functions:
  98  * radix_tree_lookup
  99  * radix_tree_tag_get
 100  * radix_tree_gang_lookup
 101  * radix_tree_gang_lookup_tag
 102  * radix_tree_tagged
 103  *
 104  * The first 4 functions are able to be called locklessly, using RCU. The
 105  * caller must ensure calls to these functions are made within rcu_read_lock()
 106  * regions. Other readers (lock-free or otherwise) and modifications may be
 107  * running concurrently.
 108  *
 109  * It is still required that the caller manage the synchronization and lifetimes
 110  * of the items. So if RCU lock-free lookups are used, typically this would mean
 111  * that the items have their own locks, or are amenable to lock-free access; and
 112  * that the items are freed by RCU (or only freed after having been deleted from
 113  * the radix tree *and* a synchronize_rcu() grace period).
 114  *
 115  * (Note, rcu_assign_pointer and rcu_dereference are not needed to control
 116  * access to data items when inserting into or looking up from the radix tree)
 117  *
 118  * radix_tree_tagged is able to be called without locking or RCU.
 119  */
 120
 121 /**
 122  * radix_tree_deref_slot        - dereference a slot
 123  * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 124  * Returns:     item that was stored in that slot with any direct pointer flag
 125  *              removed.
 126  *
 127  * For use with radix_tree_lookup_slot().  Caller must hold tree at least read
 128  * locked across slot lookup and dereference.  More likely, will be used with
 129  * radix_tree_replace_slot(), as well, so caller will hold tree write locked.
 130  */
 131 static inline void *radix_tree_deref_slot(void **pslot)
 132 {
 133         return radix_tree_direct_to_ptr(*pslot);
 134 }
 135 /**
 136  * radix_tree_replace_slot      - replace item in a slot
 137  * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 138  * @item:       new item to store in the slot.
 139  *
 140  * For use with radix_tree_lookup_slot().  Caller must hold tree write locked
 141  * across slot lookup and replacement.
 142  */
 143 static inline void radix_tree_replace_slot(void **pslot, void *item)
 144 {
 145         BUG_ON(radix_tree_is_direct_ptr(item));
 146         rcu_assign_pointer(*pslot,
 147                 (void *)((unsigned long)item |
 148                         ((unsigned long)*pslot & RADIX_TREE_DIRECT_PTR)));
 149 }
 150
 151 int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
 152 void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
 153 void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
 154 void *radix_tree_delete(struct radix_tree_root *, unsigned long);
 155 unsigned int
 156 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
 157                         unsigned long first_index, unsigned int max_items);
 158 int radix_tree_preload(gfp_t gfp_mask);
 159 void radix_tree_init(void);
 160 void *radix_tree_tag_set(struct radix_tree_root *root,
 161                         unsigned long index, unsigned int tag);
 162 void *radix_tree_tag_clear(struct radix_tree_root *root,
 163                         unsigned long index, unsigned int tag);
 164 int radix_tree_tag_get(struct radix_tree_root *root,
 165                         unsigned long index, unsigned int tag);
 166 unsigned int
 167 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
 168                 unsigned long first_index, unsigned int max_items,
 169                 unsigned int tag);
 170 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);
 171
 172 static inline void radix_tree_preload_end(void)
 173 {
 174         preempt_enable();
 175 }
 176
 177 #endif /* _LINUX_RADIX_TREE_H */