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  * An indirect pointer (root->rnode pointing to a radix_tree_node, rather
  30  * than a data item) is signalled by the low bit set in the root->rnode
  31  * pointer.
  32  *
  33  * In this case root->height is > 0, but the indirect pointer tests are
  34  * needed for RCU lookups (because root->height is unreliable). The only
  35  * time callers need worry about this is when doing a lookup_slot under
  36  * RCU.
  37  */
  38 #define RADIX_TREE_INDIRECT_PTR 1
  39 #define RADIX_TREE_RETRY ((void *)-1UL)
  40
  41 static inline void *radix_tree_ptr_to_indirect(void *ptr)
  42 {
  43         return (void *)((unsigned long)ptr | RADIX_TREE_INDIRECT_PTR);
  44 }
  45
  46 static inline void *radix_tree_indirect_to_ptr(void *ptr)
  47 {
  48         return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_PTR);
  49 }
  50
  51 static inline int radix_tree_is_indirect_ptr(void *ptr)
  52 {
  53         return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
  54 }
  55
  56 /*** radix-tree API starts here ***/
  57
  58 #define RADIX_TREE_MAX_TAGS 2
  59
  60 /* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
  61 struct radix_tree_root {
  62         unsigned int            height;
  63         gfp_t                   gfp_mask;
  64         struct radix_tree_node  *rnode;
  65 };
  66
  67 #define RADIX_TREE_INIT(mask)   {                                       \
  68         .height = 0,                                                    \
  69         .gfp_mask = (mask),                                             \
  70         .rnode = NULL,                                                  \
  71 }
  72
  73 #define RADIX_TREE(name, mask) \
  74         struct radix_tree_root name = RADIX_TREE_INIT(mask)
  75
  76 #define INIT_RADIX_TREE(root, mask)                                     \
  77 do {                                                                    \
  78         (root)->height = 0;                                             \
  79         (root)->gfp_mask = (mask);                                      \
  80         (root)->rnode = NULL;                                           \
  81 } while (0)
  82
  83 /**
  84  * Radix-tree synchronization
  85  *
  86  * The radix-tree API requires that users provide all synchronisation (with
  87  * specific exceptions, noted below).
  88  *
  89  * Synchronization of access to the data items being stored in the tree, and
  90  * management of their lifetimes must be completely managed by API users.
  91  *
  92  * For API usage, in general,
  93  * - any function _modifying_ the tree or tags (inserting or deleting
  94  *   items, setting or clearing tags) must exclude other modifications, and
  95  *   exclude any functions reading the tree.
  96  * - any function _reading_ the tree or tags (looking up items or tags,
  97  *   gang lookups) must exclude modifications to the tree, but may occur
  98  *   concurrently with other readers.
  99  *
 100  * The notable exceptions to this rule are the following functions:
 101  * radix_tree_lookup
 102  * radix_tree_lookup_slot
 103  * radix_tree_tag_get
 104  * radix_tree_gang_lookup
 105  * radix_tree_gang_lookup_slot
 106  * radix_tree_gang_lookup_tag
 107  * radix_tree_gang_lookup_tag_slot
 108  * radix_tree_tagged
 109  *
 110  * The first 7 functions are able to be called locklessly, using RCU. The
 111  * caller must ensure calls to these functions are made within rcu_read_lock()
 112  * regions. Other readers (lock-free or otherwise) and modifications may be
 113  * running concurrently.
 114  *
 115  * It is still required that the caller manage the synchronization and lifetimes
 116  * of the items. So if RCU lock-free lookups are used, typically this would mean
 117  * that the items have their own locks, or are amenable to lock-free access; and
 118  * that the items are freed by RCU (or only freed after having been deleted from
 119  * the radix tree *and* a synchronize_rcu() grace period).
 120  *
 121  * (Note, rcu_assign_pointer and rcu_dereference are not needed to control
 122  * access to data items when inserting into or looking up from the radix tree)
 123  *
 124  * Note that the value returned by radix_tree_tag_get() may not be relied upon
 125  * if only the RCU read lock is held.  Functions to set/clear tags and to
 126  * delete nodes running concurrently with it may affect its result such that
 127  * two consecutive reads in the same locked section may return different
 128  * values.  If reliability is required, modification functions must also be
 129  * excluded from concurrency.
 130  *
 131  * radix_tree_tagged is able to be called without locking or RCU.
 132  */
 133
 134 /**
 135  * radix_tree_deref_slot        - dereference a slot
 136  * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 137  * Returns:     item that was stored in that slot with any direct pointer flag
 138  *              removed.
 139  *
 140  * For use with radix_tree_lookup_slot().  Caller must hold tree at least read
 141  * locked across slot lookup and dereference.  More likely, will be used with
 142  * radix_tree_replace_slot(), as well, so caller will hold tree write locked.
 143  */
 144 static inline void *radix_tree_deref_slot(void **pslot)
 145 {
 146         void *ret = rcu_dereference(*pslot);
 147         if (unlikely(radix_tree_is_indirect_ptr(ret)))
 148                 ret = RADIX_TREE_RETRY;
 149         return ret;
 150 }
 151 /**
 152  * radix_tree_replace_slot      - replace item in a slot
 153  * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 154  * @item:       new item to store in the slot.
 155  *
 156  * For use with radix_tree_lookup_slot().  Caller must hold tree write locked
 157  * across slot lookup and replacement.
 158  */
 159 static inline void radix_tree_replace_slot(void **pslot, void *item)
 160 {
 161         BUG_ON(radix_tree_is_indirect_ptr(item));
 162         rcu_assign_pointer(*pslot, item);
 163 }
 164
 165 int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
 166 void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
 167 void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
 168 void *radix_tree_delete(struct radix_tree_root *, unsigned long);
 169 unsigned int
 170 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
 171                         unsigned long first_index, unsigned int max_items);
 172 unsigned int
 173 radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
 174                         unsigned long first_index, unsigned int max_items);
 175 unsigned long radix_tree_next_hole(struct radix_tree_root *root,
 176                                 unsigned long index, unsigned long max_scan);
 177 unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
 178                                 unsigned long index, unsigned long max_scan);
 179 int radix_tree_preload(gfp_t gfp_mask);
 180 void radix_tree_init(void);
 181 void *radix_tree_tag_set(struct radix_tree_root *root,
 182                         unsigned long index, unsigned int tag);
 183 void *radix_tree_tag_clear(struct radix_tree_root *root,
 184                         unsigned long index, unsigned int tag);
 185 int radix_tree_tag_get(struct radix_tree_root *root,
 186                         unsigned long index, unsigned int tag);
 187 unsigned int
 188 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
 189                 unsigned long first_index, unsigned int max_items,
 190                 unsigned int tag);
 191 unsigned int
 192 radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
 193                 unsigned long first_index, unsigned int max_items,
 194                 unsigned int tag);
 195 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);
 196
 197 static inline void radix_tree_preload_end(void)
 198 {
 199         preempt_enable();
 200 }
 201
 202 #endif /* _LINUX_RADIX_TREE_H */