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  * Indirect pointer in fact is also used to tag the last pointer of a node
  39  * when it is shrunk, before we rcu free the node. See shrink code for
  40  * details.
  41  */
  42 #define RADIX_TREE_INDIRECT_PTR 1
  43
  44 #define radix_tree_indirect_to_ptr(ptr) \
  45         radix_tree_indirect_to_ptr((void __force *)(ptr))
  46
  47 static inline int radix_tree_is_indirect_ptr(void *ptr)
  48 {
  49         return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
  50 }
  51
  52 /*** radix-tree API starts here ***/
  53
  54 #define RADIX_TREE_MAX_TAGS 3
  55
  56 /* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
  57 struct radix_tree_root {
  58         unsigned int            height;
  59         gfp_t                   gfp_mask;
  60         struct radix_tree_node  __rcu *rnode;
  61 };
  62
  63 #define RADIX_TREE_INIT(mask)   {                                       \
  64         .height = 0,                                                    \
  65         .gfp_mask = (mask),                                             \
  66         .rnode = NULL,                                                  \
  67 }
  68
  69 #define RADIX_TREE(name, mask) \
  70         struct radix_tree_root name = RADIX_TREE_INIT(mask)
  71
  72 #define INIT_RADIX_TREE(root, mask)                                     \
  73 do {                                                                    \
  74         (root)->height = 0;                                             \
  75         (root)->gfp_mask = (mask);                                      \
  76         (root)->rnode = NULL;                                           \
  77 } while (0)
  78
  79 /**
  80  * Radix-tree synchronization
  81  *
  82  * The radix-tree API requires that users provide all synchronisation (with
  83  * specific exceptions, noted below).
  84  *
  85  * Synchronization of access to the data items being stored in the tree, and
  86  * management of their lifetimes must be completely managed by API users.
  87  *
  88  * For API usage, in general,
  89  * - any function _modifying_ the tree or tags (inserting or deleting
  90  *   items, setting or clearing tags) must exclude other modifications, and
  91  *   exclude any functions reading the tree.
  92  * - any function _reading_ the tree or tags (looking up items or tags,
  93  *   gang lookups) must exclude modifications to the tree, but may occur
  94  *   concurrently with other readers.
  95  *
  96  * The notable exceptions to this rule are the following functions:
  97  * radix_tree_lookup
  98  * radix_tree_lookup_slot
  99  * radix_tree_tag_get
 100  * radix_tree_gang_lookup
 101  * radix_tree_gang_lookup_slot
 102  * radix_tree_gang_lookup_tag
 103  * radix_tree_gang_lookup_tag_slot
 104  * radix_tree_tagged
 105  *
 106  * The first 7 functions are able to be called locklessly, using RCU. The
 107  * caller must ensure calls to these functions are made within rcu_read_lock()
 108  * regions. Other readers (lock-free or otherwise) and modifications may be
 109  * running concurrently.
 110  *
 111  * It is still required that the caller manage the synchronization and lifetimes
 112  * of the items. So if RCU lock-free lookups are used, typically this would mean
 113  * that the items have their own locks, or are amenable to lock-free access; and
 114  * that the items are freed by RCU (or only freed after having been deleted from
 115  * the radix tree *and* a synchronize_rcu() grace period).
 116  *
 117  * (Note, rcu_assign_pointer and rcu_dereference are not needed to control
 118  * access to data items when inserting into or looking up from the radix tree)
 119  *
 120  * Note that the value returned by radix_tree_tag_get() may not be relied upon
 121  * if only the RCU read lock is held.  Functions to set/clear tags and to
 122  * delete nodes running concurrently with it may affect its result such that
 123  * two consecutive reads in the same locked section may return different
 124  * values.  If reliability is required, modification functions must also be
 125  * excluded from concurrency.
 126  *
 127  * radix_tree_tagged is able to be called without locking or RCU.
 128  */
 129
 130 /**
 131  * radix_tree_deref_slot        - dereference a slot
 132  * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 133  * Returns:     item that was stored in that slot with any direct pointer flag
 134  *              removed.
 135  *
 136  * For use with radix_tree_lookup_slot().  Caller must hold tree at least read
 137  * locked across slot lookup and dereference. Not required if write lock is
 138  * held (ie. items cannot be concurrently inserted).
 139  *
 140  * radix_tree_deref_retry must be used to confirm validity of the pointer if
 141  * only the read lock is held.
 142  */
 143 static inline void *radix_tree_deref_slot(void **pslot)
 144 {
 145         return rcu_dereference(*pslot);
 146 }
 147
 148 /**
 149  * radix_tree_deref_slot_protected      - dereference a slot without RCU lock but with tree lock held
 150  * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 151  * Returns:     item that was stored in that slot with any direct pointer flag
 152  *              removed.
 153  *
 154  * Similar to radix_tree_deref_slot but only used during migration when a pages
 155  * mapping is being moved. The caller does not hold the RCU read lock but it
 156  * must hold the tree lock to prevent parallel updates.
 157  */
 158 static inline void *radix_tree_deref_slot_protected(void **pslot,
 159                                                         spinlock_t *treelock)
 160 {
 161         return rcu_dereference_protected(*pslot, lockdep_is_held(treelock));
 162 }
 163
 164 /**
 165  * radix_tree_deref_retry       - check radix_tree_deref_slot
 166  * @arg:        pointer returned by radix_tree_deref_slot
 167  * Returns:     0 if retry is not required, otherwise retry is required
 168  *
 169  * radix_tree_deref_retry must be used with radix_tree_deref_slot.
 170  */
 171 static inline int radix_tree_deref_retry(void *arg)
 172 {
 173         return unlikely((unsigned long)arg & RADIX_TREE_INDIRECT_PTR);
 174 }
 175
 176 /**
 177  * radix_tree_replace_slot      - replace item in a slot
 178  * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 179  * @item:       new item to store in the slot.
 180  *
 181  * For use with radix_tree_lookup_slot().  Caller must hold tree write locked
 182  * across slot lookup and replacement.
 183  */
 184 static inline void radix_tree_replace_slot(void **pslot, void *item)
 185 {
 186         BUG_ON(radix_tree_is_indirect_ptr(item));
 187         rcu_assign_pointer(*pslot, item);
 188 }
 189
 190 int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
 191 void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
 192 void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
 193 void *radix_tree_delete(struct radix_tree_root *, unsigned long);
 194 unsigned int
 195 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
 196                         unsigned long first_index, unsigned int max_items);
 197 unsigned int
 198 radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
 199                         unsigned long first_index, unsigned int max_items);
 200 unsigned long radix_tree_next_hole(struct radix_tree_root *root,
 201                                 unsigned long index, unsigned long max_scan);
 202 unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
 203                                 unsigned long index, unsigned long max_scan);
 204 int radix_tree_preload(gfp_t gfp_mask);
 205 void radix_tree_init(void);
 206 void *radix_tree_tag_set(struct radix_tree_root *root,
 207                         unsigned long index, unsigned int tag);
 208 void *radix_tree_tag_clear(struct radix_tree_root *root,
 209                         unsigned long index, unsigned int tag);
 210 int radix_tree_tag_get(struct radix_tree_root *root,
 211                         unsigned long index, unsigned int tag);
 212 unsigned int
 213 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
 214                 unsigned long first_index, unsigned int max_items,
 215                 unsigned int tag);
 216 unsigned int
 217 radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
 218                 unsigned long first_index, unsigned int max_items,
 219                 unsigned int tag);
 220 unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
 221                 unsigned long *first_indexp, unsigned long last_index,
 222                 unsigned long nr_to_tag,
 223                 unsigned int fromtag, unsigned int totag);
 224 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);
 225
 226 static inline void radix_tree_preload_end(void)
 227 {
 228         preempt_enable();
 229 }
 230
 231 #endif /* _LINUX_RADIX_TREE_H */