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/bug.h>
  26 #include <linux/kernel.h>
  27 #include <linux/rcupdate.h>
  28
  29 /*
  30  * An indirect pointer (root->rnode pointing to a radix_tree_node, rather
  31  * than a data item) is signalled by the low bit set in the root->rnode
  32  * pointer.
  33  *
  34  * In this case root->height is > 0, but the indirect pointer tests are
  35  * needed for RCU lookups (because root->height is unreliable). The only
  36  * time callers need worry about this is when doing a lookup_slot under
  37  * RCU.
  38  *
  39  * Indirect pointer in fact is also used to tag the last pointer of a node
  40  * when it is shrunk, before we rcu free the node. See shrink code for
  41  * details.
  42  */
  43 #define RADIX_TREE_INDIRECT_PTR         1
  44 /*
  45  * A common use of the radix tree is to store pointers to struct pages;
  46  * but shmem/tmpfs needs also to store swap entries in the same tree:
  47  * those are marked as exceptional entries to distinguish them.
  48  * EXCEPTIONAL_ENTRY tests the bit, EXCEPTIONAL_SHIFT shifts content past it.
  49  */
  50 #define RADIX_TREE_EXCEPTIONAL_ENTRY    2
  51 #define RADIX_TREE_EXCEPTIONAL_SHIFT    2
  52
  53 static inline int radix_tree_is_indirect_ptr(void *ptr)
  54 {
  55         return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
  56 }
  57
  58 /*** radix-tree API starts here ***/
  59
  60 #define RADIX_TREE_MAX_TAGS 3
  61
  62 /* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
  63 struct radix_tree_root {
  64         unsigned int            height;
  65         gfp_t                   gfp_mask;
  66         struct radix_tree_node  __rcu *rnode;
  67 };
  68
  69 #define RADIX_TREE_INIT(mask)   {                                       \
  70         .height = 0,                                                    \
  71         .gfp_mask = (mask),                                             \
  72         .rnode = NULL,                                                  \
  73 }
  74
  75 #define RADIX_TREE(name, mask) \
  76         struct radix_tree_root name = RADIX_TREE_INIT(mask)
  77
  78 #define INIT_RADIX_TREE(root, mask)                                     \
  79 do {                                                                    \
  80         (root)->height = 0;                                             \
  81         (root)->gfp_mask = (mask);                                      \
  82         (root)->rnode = NULL;                                           \
  83 } while (0)
  84
  85 /**
  86  * Radix-tree synchronization
  87  *
  88  * The radix-tree API requires that users provide all synchronisation (with
  89  * specific exceptions, noted below).
  90  *
  91  * Synchronization of access to the data items being stored in the tree, and
  92  * management of their lifetimes must be completely managed by API users.
  93  *
  94  * For API usage, in general,
  95  * - any function _modifying_ the tree or tags (inserting or deleting
  96  *   items, setting or clearing tags) must exclude other modifications, and
  97  *   exclude any functions reading the tree.
  98  * - any function _reading_ the tree or tags (looking up items or tags,
  99  *   gang lookups) must exclude modifications to the tree, but may occur
 100  *   concurrently with other readers.
 101  *
 102  * The notable exceptions to this rule are the following functions:
 103  * radix_tree_lookup
 104  * radix_tree_lookup_slot
 105  * radix_tree_tag_get
 106  * radix_tree_gang_lookup
 107  * radix_tree_gang_lookup_slot
 108  * radix_tree_gang_lookup_tag
 109  * radix_tree_gang_lookup_tag_slot
 110  * radix_tree_tagged
 111  *
 112  * The first 7 functions are able to be called locklessly, using RCU. The
 113  * caller must ensure calls to these functions are made within rcu_read_lock()
 114  * regions. Other readers (lock-free or otherwise) and modifications may be
 115  * running concurrently.
 116  *
 117  * It is still required that the caller manage the synchronization and lifetimes
 118  * of the items. So if RCU lock-free lookups are used, typically this would mean
 119  * that the items have their own locks, or are amenable to lock-free access; and
 120  * that the items are freed by RCU (or only freed after having been deleted from
 121  * the radix tree *and* a synchronize_rcu() grace period).
 122  *
 123  * (Note, rcu_assign_pointer and rcu_dereference are not needed to control
 124  * access to data items when inserting into or looking up from the radix tree)
 125  *
 126  * Note that the value returned by radix_tree_tag_get() may not be relied upon
 127  * if only the RCU read lock is held.  Functions to set/clear tags and to
 128  * delete nodes running concurrently with it may affect its result such that
 129  * two consecutive reads in the same locked section may return different
 130  * values.  If reliability is required, modification functions must also be
 131  * excluded from concurrency.
 132  *
 133  * radix_tree_tagged is able to be called without locking or RCU.
 134  */
 135
 136 /**
 137  * radix_tree_deref_slot        - dereference a slot
 138  * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 139  * Returns:     item that was stored in that slot with any direct pointer flag
 140  *              removed.
 141  *
 142  * For use with radix_tree_lookup_slot().  Caller must hold tree at least read
 143  * locked across slot lookup and dereference. Not required if write lock is
 144  * held (ie. items cannot be concurrently inserted).
 145  *
 146  * radix_tree_deref_retry must be used to confirm validity of the pointer if
 147  * only the read lock is held.
 148  */
 149 static inline void *radix_tree_deref_slot(void **pslot)
 150 {
 151         return rcu_dereference(*pslot);
 152 }
 153
 154 /**
 155  * radix_tree_deref_slot_protected      - dereference a slot without RCU lock but with tree lock held
 156  * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 157  * Returns:     item that was stored in that slot with any direct pointer flag
 158  *              removed.
 159  *
 160  * Similar to radix_tree_deref_slot but only used during migration when a pages
 161  * mapping is being moved. The caller does not hold the RCU read lock but it
 162  * must hold the tree lock to prevent parallel updates.
 163  */
 164 static inline void *radix_tree_deref_slot_protected(void **pslot,
 165                                                         spinlock_t *treelock)
 166 {
 167         return rcu_dereference_protected(*pslot, lockdep_is_held(treelock));
 168 }
 169
 170 /**
 171  * radix_tree_deref_retry       - check radix_tree_deref_slot
 172  * @arg:        pointer returned by radix_tree_deref_slot
 173  * Returns:     0 if retry is not required, otherwise retry is required
 174  *
 175  * radix_tree_deref_retry must be used with radix_tree_deref_slot.
 176  */
 177 static inline int radix_tree_deref_retry(void *arg)
 178 {
 179         return unlikely((unsigned long)arg & RADIX_TREE_INDIRECT_PTR);
 180 }
 181
 182 /**
 183  * radix_tree_exceptional_entry - radix_tree_deref_slot gave exceptional entry?
 184  * @arg:        value returned by radix_tree_deref_slot
 185  * Returns:     0 if well-aligned pointer, non-0 if exceptional entry.
 186  */
 187 static inline int radix_tree_exceptional_entry(void *arg)
 188 {
 189         /* Not unlikely because radix_tree_exception often tested first */
 190         return (unsigned long)arg & RADIX_TREE_EXCEPTIONAL_ENTRY;
 191 }
 192
 193 /**
 194  * radix_tree_exception - radix_tree_deref_slot returned either exception?
 195  * @arg:        value returned by radix_tree_deref_slot
 196  * Returns:     0 if well-aligned pointer, non-0 if either kind of exception.
 197  */
 198 static inline int radix_tree_exception(void *arg)
 199 {
 200         return unlikely((unsigned long)arg &
 201                 (RADIX_TREE_INDIRECT_PTR | RADIX_TREE_EXCEPTIONAL_ENTRY));
 202 }
 203
 204 /**
 205  * radix_tree_replace_slot      - replace item in a slot
 206  * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 207  * @item:       new item to store in the slot.
 208  *
 209  * For use with radix_tree_lookup_slot().  Caller must hold tree write locked
 210  * across slot lookup and replacement.
 211  */
 212 static inline void radix_tree_replace_slot(void **pslot, void *item)
 213 {
 214         BUG_ON(radix_tree_is_indirect_ptr(item));
 215         rcu_assign_pointer(*pslot, item);
 216 }
 217
 218 int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
 219 void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
 220 void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
 221 void *radix_tree_delete(struct radix_tree_root *, unsigned long);
 222 unsigned int
 223 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
 224                         unsigned long first_index, unsigned int max_items);
 225 unsigned int radix_tree_gang_lookup_slot(struct radix_tree_root *root,
 226                         void ***results, unsigned long *indices,
 227                         unsigned long first_index, unsigned int max_items);
 228 unsigned long radix_tree_next_hole(struct radix_tree_root *root,
 229                                 unsigned long index, unsigned long max_scan);
 230 unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
 231                                 unsigned long index, unsigned long max_scan);
 232 int radix_tree_preload(gfp_t gfp_mask);
 233 void radix_tree_init(void);
 234 void *radix_tree_tag_set(struct radix_tree_root *root,
 235                         unsigned long index, unsigned int tag);
 236 void *radix_tree_tag_clear(struct radix_tree_root *root,
 237                         unsigned long index, unsigned int tag);
 238 int radix_tree_tag_get(struct radix_tree_root *root,
 239                         unsigned long index, unsigned int tag);
 240 unsigned int
 241 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
 242                 unsigned long first_index, unsigned int max_items,
 243                 unsigned int tag);
 244 unsigned int
 245 radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
 246                 unsigned long first_index, unsigned int max_items,
 247                 unsigned int tag);
 248 unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
 249                 unsigned long *first_indexp, unsigned long last_index,
 250                 unsigned long nr_to_tag,
 251                 unsigned int fromtag, unsigned int totag);
 252 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);
 253 unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item);
 254
 255 static inline void radix_tree_preload_end(void)
 256 {
 257         preempt_enable();
 258 }
 259
 260 #endif /* _LINUX_RADIX_TREE_H */