linux/include/linux/radix-tree.h
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   1/*
   2 * Copyright (C) 2001 Momchil Velikov
   3 * Portions Copyright (C) 2001 Christoph Hellwig
   4 * Copyright (C) 2006 Nick Piggin
   5 * Copyright (C) 2012 Konstantin Khlebnikov
   6 *
   7 * This program is free software; you can redistribute it and/or
   8 * modify it under the terms of the GNU General Public License as
   9 * published by the Free Software Foundation; either version 2, or (at
  10 * your option) any later version.
  11 * 
  12 * This program is distributed in the hope that it will be useful, but
  13 * WITHOUT ANY WARRANTY; without even the implied warranty of
  14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 * General Public License for more details.
  16 * 
  17 * You should have received a copy of the GNU General Public License
  18 * along with this program; if not, write to the Free Software
  19 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20 */
  21#ifndef _LINUX_RADIX_TREE_H
  22#define _LINUX_RADIX_TREE_H
  23
  24#include <linux/preempt.h>
  25#include <linux/types.h>
  26#include <linux/bug.h>
  27#include <linux/kernel.h>
  28#include <linux/rcupdate.h>
  29
  30/*
  31 * An indirect pointer (root->rnode pointing to a radix_tree_node, rather
  32 * than a data item) is signalled by the low bit set in the root->rnode
  33 * pointer.
  34 *
  35 * In this case root->height is > 0, but the indirect pointer tests are
  36 * needed for RCU lookups (because root->height is unreliable). The only
  37 * time callers need worry about this is when doing a lookup_slot under
  38 * RCU.
  39 *
  40 * Indirect pointer in fact is also used to tag the last pointer of a node
  41 * when it is shrunk, before we rcu free the node. See shrink code for
  42 * details.
  43 */
  44#define RADIX_TREE_INDIRECT_PTR         1
  45/*
  46 * A common use of the radix tree is to store pointers to struct pages;
  47 * but shmem/tmpfs needs also to store swap entries in the same tree:
  48 * those are marked as exceptional entries to distinguish them.
  49 * EXCEPTIONAL_ENTRY tests the bit, EXCEPTIONAL_SHIFT shifts content past it.
  50 */
  51#define RADIX_TREE_EXCEPTIONAL_ENTRY    2
  52#define RADIX_TREE_EXCEPTIONAL_SHIFT    2
  53
  54static inline int radix_tree_is_indirect_ptr(void *ptr)
  55{
  56        return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
  57}
  58
  59/*** radix-tree API starts here ***/
  60
  61#define RADIX_TREE_MAX_TAGS 3
  62
  63/* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
  64struct radix_tree_root {
  65        unsigned int            height;
  66        gfp_t                   gfp_mask;
  67        struct radix_tree_node  __rcu *rnode;
  68};
  69
  70#define RADIX_TREE_INIT(mask)   {                                       \
  71        .height = 0,                                                    \
  72        .gfp_mask = (mask),                                             \
  73        .rnode = NULL,                                                  \
  74}
  75
  76#define RADIX_TREE(name, mask) \
  77        struct radix_tree_root name = RADIX_TREE_INIT(mask)
  78
  79#define INIT_RADIX_TREE(root, mask)                                     \
  80do {                                                                    \
  81        (root)->height = 0;                                             \
  82        (root)->gfp_mask = (mask);                                      \
  83        (root)->rnode = NULL;                                           \
  84} while (0)
  85
  86/**
  87 * Radix-tree synchronization
  88 *
  89 * The radix-tree API requires that users provide all synchronisation (with
  90 * specific exceptions, noted below).
  91 *
  92 * Synchronization of access to the data items being stored in the tree, and
  93 * management of their lifetimes must be completely managed by API users.
  94 *
  95 * For API usage, in general,
  96 * - any function _modifying_ the tree or tags (inserting or deleting
  97 *   items, setting or clearing tags) must exclude other modifications, and
  98 *   exclude any functions reading the tree.
  99 * - any function _reading_ the tree or tags (looking up items or tags,
 100 *   gang lookups) must exclude modifications to the tree, but may occur
 101 *   concurrently with other readers.
 102 *
 103 * The notable exceptions to this rule are the following functions:
 104 * radix_tree_lookup
 105 * radix_tree_lookup_slot
 106 * radix_tree_tag_get
 107 * radix_tree_gang_lookup
 108 * radix_tree_gang_lookup_slot
 109 * radix_tree_gang_lookup_tag
 110 * radix_tree_gang_lookup_tag_slot
 111 * radix_tree_tagged
 112 *
 113 * The first 7 functions are able to be called locklessly, using RCU. The
 114 * caller must ensure calls to these functions are made within rcu_read_lock()
 115 * regions. Other readers (lock-free or otherwise) and modifications may be
 116 * running concurrently.
 117 *
 118 * It is still required that the caller manage the synchronization and lifetimes
 119 * of the items. So if RCU lock-free lookups are used, typically this would mean
 120 * that the items have their own locks, or are amenable to lock-free access; and
 121 * that the items are freed by RCU (or only freed after having been deleted from
 122 * the radix tree *and* a synchronize_rcu() grace period).
 123 *
 124 * (Note, rcu_assign_pointer and rcu_dereference are not needed to control
 125 * access to data items when inserting into or looking up from the radix tree)
 126 *
 127 * Note that the value returned by radix_tree_tag_get() may not be relied upon
 128 * if only the RCU read lock is held.  Functions to set/clear tags and to
 129 * delete nodes running concurrently with it may affect its result such that
 130 * two consecutive reads in the same locked section may return different
 131 * values.  If reliability is required, modification functions must also be
 132 * excluded from concurrency.
 133 *
 134 * radix_tree_tagged is able to be called without locking or RCU.
 135 */
 136
 137/**
 138 * radix_tree_deref_slot        - dereference a slot
 139 * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 140 * Returns:     item that was stored in that slot with any direct pointer flag
 141 *              removed.
 142 *
 143 * For use with radix_tree_lookup_slot().  Caller must hold tree at least read
 144 * locked across slot lookup and dereference. Not required if write lock is
 145 * held (ie. items cannot be concurrently inserted).
 146 *
 147 * radix_tree_deref_retry must be used to confirm validity of the pointer if
 148 * only the read lock is held.
 149 */
 150static inline void *radix_tree_deref_slot(void **pslot)
 151{
 152        return rcu_dereference(*pslot);
 153}
 154
 155/**
 156 * radix_tree_deref_slot_protected      - dereference a slot without RCU lock but with tree lock held
 157 * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 158 * Returns:     item that was stored in that slot with any direct pointer flag
 159 *              removed.
 160 *
 161 * Similar to radix_tree_deref_slot but only used during migration when a pages
 162 * mapping is being moved. The caller does not hold the RCU read lock but it
 163 * must hold the tree lock to prevent parallel updates.
 164 */
 165static inline void *radix_tree_deref_slot_protected(void **pslot,
 166                                                        spinlock_t *treelock)
 167{
 168        return rcu_dereference_protected(*pslot, lockdep_is_held(treelock));
 169}
 170
 171/**
 172 * radix_tree_deref_retry       - check radix_tree_deref_slot
 173 * @arg:        pointer returned by radix_tree_deref_slot
 174 * Returns:     0 if retry is not required, otherwise retry is required
 175 *
 176 * radix_tree_deref_retry must be used with radix_tree_deref_slot.
 177 */
 178static inline int radix_tree_deref_retry(void *arg)
 179{
 180        return unlikely((unsigned long)arg & RADIX_TREE_INDIRECT_PTR);
 181}
 182
 183/**
 184 * radix_tree_exceptional_entry - radix_tree_deref_slot gave exceptional entry?
 185 * @arg:        value returned by radix_tree_deref_slot
 186 * Returns:     0 if well-aligned pointer, non-0 if exceptional entry.
 187 */
 188static inline int radix_tree_exceptional_entry(void *arg)
 189{
 190        /* Not unlikely because radix_tree_exception often tested first */
 191        return (unsigned long)arg & RADIX_TREE_EXCEPTIONAL_ENTRY;
 192}
 193
 194/**
 195 * radix_tree_exception - radix_tree_deref_slot returned either exception?
 196 * @arg:        value returned by radix_tree_deref_slot
 197 * Returns:     0 if well-aligned pointer, non-0 if either kind of exception.
 198 */
 199static inline int radix_tree_exception(void *arg)
 200{
 201        return unlikely((unsigned long)arg &
 202                (RADIX_TREE_INDIRECT_PTR | RADIX_TREE_EXCEPTIONAL_ENTRY));
 203}
 204
 205/**
 206 * radix_tree_replace_slot      - replace item in a slot
 207 * @pslot:      pointer to slot, returned by radix_tree_lookup_slot
 208 * @item:       new item to store in the slot.
 209 *
 210 * For use with radix_tree_lookup_slot().  Caller must hold tree write locked
 211 * across slot lookup and replacement.
 212 */
 213static inline void radix_tree_replace_slot(void **pslot, void *item)
 214{
 215        BUG_ON(radix_tree_is_indirect_ptr(item));
 216        rcu_assign_pointer(*pslot, item);
 217}
 218
 219int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
 220void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
 221void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
 222void *radix_tree_delete(struct radix_tree_root *, unsigned long);
 223unsigned int
 224radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
 225                        unsigned long first_index, unsigned int max_items);
 226unsigned int radix_tree_gang_lookup_slot(struct radix_tree_root *root,
 227                        void ***results, unsigned long *indices,
 228                        unsigned long first_index, unsigned int max_items);
 229unsigned long radix_tree_next_hole(struct radix_tree_root *root,
 230                                unsigned long index, unsigned long max_scan);
 231unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
 232                                unsigned long index, unsigned long max_scan);
 233int radix_tree_preload(gfp_t gfp_mask);
 234void radix_tree_init(void);
 235void *radix_tree_tag_set(struct radix_tree_root *root,
 236                        unsigned long index, unsigned int tag);
 237void *radix_tree_tag_clear(struct radix_tree_root *root,
 238                        unsigned long index, unsigned int tag);
 239int radix_tree_tag_get(struct radix_tree_root *root,
 240                        unsigned long index, unsigned int tag);
 241unsigned int
 242radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
 243                unsigned long first_index, unsigned int max_items,
 244                unsigned int tag);
 245unsigned int
 246radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
 247                unsigned long first_index, unsigned int max_items,
 248                unsigned int tag);
 249unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
 250                unsigned long *first_indexp, unsigned long last_index,
 251                unsigned long nr_to_tag,
 252                unsigned int fromtag, unsigned int totag);
 253int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);
 254unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item);
 255
 256static inline void radix_tree_preload_end(void)
 257{
 258        preempt_enable();
 259}
 260
 261/**
 262 * struct radix_tree_iter - radix tree iterator state
 263 *
 264 * @index:      index of current slot
 265 * @next_index: next-to-last index for this chunk
 266 * @tags:       bit-mask for tag-iterating
 267 *
 268 * This radix tree iterator works in terms of "chunks" of slots.  A chunk is a
 269 * subinterval of slots contained within one radix tree leaf node.  It is
 270 * described by a pointer to its first slot and a struct radix_tree_iter
 271 * which holds the chunk's position in the tree and its size.  For tagged
 272 * iteration radix_tree_iter also holds the slots' bit-mask for one chosen
 273 * radix tree tag.
 274 */
 275struct radix_tree_iter {
 276        unsigned long   index;
 277        unsigned long   next_index;
 278        unsigned long   tags;
 279};
 280
 281#define RADIX_TREE_ITER_TAG_MASK        0x00FF  /* tag index in lower byte */
 282#define RADIX_TREE_ITER_TAGGED          0x0100  /* lookup tagged slots */
 283#define RADIX_TREE_ITER_CONTIG          0x0200  /* stop at first hole */
 284
 285/**
 286 * radix_tree_iter_init - initialize radix tree iterator
 287 *
 288 * @iter:       pointer to iterator state
 289 * @start:      iteration starting index
 290 * Returns:     NULL
 291 */
 292static __always_inline void **
 293radix_tree_iter_init(struct radix_tree_iter *iter, unsigned long start)
 294{
 295        /*
 296         * Leave iter->tags uninitialized. radix_tree_next_chunk() will fill it
 297         * in the case of a successful tagged chunk lookup.  If the lookup was
 298         * unsuccessful or non-tagged then nobody cares about ->tags.
 299         *
 300         * Set index to zero to bypass next_index overflow protection.
 301         * See the comment in radix_tree_next_chunk() for details.
 302         */
 303        iter->index = 0;
 304        iter->next_index = start;
 305        return NULL;
 306}
 307
 308/**
 309 * radix_tree_next_chunk - find next chunk of slots for iteration
 310 *
 311 * @root:       radix tree root
 312 * @iter:       iterator state
 313 * @flags:      RADIX_TREE_ITER_* flags and tag index
 314 * Returns:     pointer to chunk first slot, or NULL if there no more left
 315 *
 316 * This function looks up the next chunk in the radix tree starting from
 317 * @iter->next_index.  It returns a pointer to the chunk's first slot.
 318 * Also it fills @iter with data about chunk: position in the tree (index),
 319 * its end (next_index), and constructs a bit mask for tagged iterating (tags).
 320 */
 321void **radix_tree_next_chunk(struct radix_tree_root *root,
 322                             struct radix_tree_iter *iter, unsigned flags);
 323
 324/**
 325 * radix_tree_chunk_size - get current chunk size
 326 *
 327 * @iter:       pointer to radix tree iterator
 328 * Returns:     current chunk size
 329 */
 330static __always_inline unsigned
 331radix_tree_chunk_size(struct radix_tree_iter *iter)
 332{
 333        return iter->next_index - iter->index;
 334}
 335
 336/**
 337 * radix_tree_next_slot - find next slot in chunk
 338 *
 339 * @slot:       pointer to current slot
 340 * @iter:       pointer to interator state
 341 * @flags:      RADIX_TREE_ITER_*, should be constant
 342 * Returns:     pointer to next slot, or NULL if there no more left
 343 *
 344 * This function updates @iter->index in the case of a successful lookup.
 345 * For tagged lookup it also eats @iter->tags.
 346 */
 347static __always_inline void **
 348radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
 349{
 350        if (flags & RADIX_TREE_ITER_TAGGED) {
 351                iter->tags >>= 1;
 352                if (likely(iter->tags & 1ul)) {
 353                        iter->index++;
 354                        return slot + 1;
 355                }
 356                if (!(flags & RADIX_TREE_ITER_CONTIG) && likely(iter->tags)) {
 357                        unsigned offset = __ffs(iter->tags);
 358
 359                        iter->tags >>= offset;
 360                        iter->index += offset + 1;
 361                        return slot + offset + 1;
 362                }
 363        } else {
 364                unsigned size = radix_tree_chunk_size(iter) - 1;
 365
 366                while (size--) {
 367                        slot++;
 368                        iter->index++;
 369                        if (likely(*slot))
 370                                return slot;
 371                        if (flags & RADIX_TREE_ITER_CONTIG) {
 372                                /* forbid switching to the next chunk */
 373                                iter->next_index = 0;
 374                                break;
 375                        }
 376                }
 377        }
 378        return NULL;
 379}
 380
 381/**
 382 * radix_tree_for_each_chunk - iterate over chunks
 383 *
 384 * @slot:       the void** variable for pointer to chunk first slot
 385 * @root:       the struct radix_tree_root pointer
 386 * @iter:       the struct radix_tree_iter pointer
 387 * @start:      iteration starting index
 388 * @flags:      RADIX_TREE_ITER_* and tag index
 389 *
 390 * Locks can be released and reacquired between iterations.
 391 */
 392#define radix_tree_for_each_chunk(slot, root, iter, start, flags)       \
 393        for (slot = radix_tree_iter_init(iter, start) ;                 \
 394              (slot = radix_tree_next_chunk(root, iter, flags)) ;)
 395
 396/**
 397 * radix_tree_for_each_chunk_slot - iterate over slots in one chunk
 398 *
 399 * @slot:       the void** variable, at the beginning points to chunk first slot
 400 * @iter:       the struct radix_tree_iter pointer
 401 * @flags:      RADIX_TREE_ITER_*, should be constant
 402 *
 403 * This macro is designed to be nested inside radix_tree_for_each_chunk().
 404 * @slot points to the radix tree slot, @iter->index contains its index.
 405 */
 406#define radix_tree_for_each_chunk_slot(slot, iter, flags)               \
 407        for (; slot ; slot = radix_tree_next_slot(slot, iter, flags))
 408
 409/**
 410 * radix_tree_for_each_slot - iterate over non-empty slots
 411 *
 412 * @slot:       the void** variable for pointer to slot
 413 * @root:       the struct radix_tree_root pointer
 414 * @iter:       the struct radix_tree_iter pointer
 415 * @start:      iteration starting index
 416 *
 417 * @slot points to radix tree slot, @iter->index contains its index.
 418 */
 419#define radix_tree_for_each_slot(slot, root, iter, start)               \
 420        for (slot = radix_tree_iter_init(iter, start) ;                 \
 421             slot || (slot = radix_tree_next_chunk(root, iter, 0)) ;    \
 422             slot = radix_tree_next_slot(slot, iter, 0))
 423
 424/**
 425 * radix_tree_for_each_contig - iterate over contiguous slots
 426 *
 427 * @slot:       the void** variable for pointer to slot
 428 * @root:       the struct radix_tree_root pointer
 429 * @iter:       the struct radix_tree_iter pointer
 430 * @start:      iteration starting index
 431 *
 432 * @slot points to radix tree slot, @iter->index contains its index.
 433 */
 434#define radix_tree_for_each_contig(slot, root, iter, start)             \
 435        for (slot = radix_tree_iter_init(iter, start) ;                 \
 436             slot || (slot = radix_tree_next_chunk(root, iter,          \
 437                                RADIX_TREE_ITER_CONTIG)) ;              \
 438             slot = radix_tree_next_slot(slot, iter,                    \
 439                                RADIX_TREE_ITER_CONTIG))
 440
 441/**
 442 * radix_tree_for_each_tagged - iterate over tagged slots
 443 *
 444 * @slot:       the void** variable for pointer to slot
 445 * @root:       the struct radix_tree_root pointer
 446 * @iter:       the struct radix_tree_iter pointer
 447 * @start:      iteration starting index
 448 * @tag:        tag index
 449 *
 450 * @slot points to radix tree slot, @iter->index contains its index.
 451 */
 452#define radix_tree_for_each_tagged(slot, root, iter, start, tag)        \
 453        for (slot = radix_tree_iter_init(iter, start) ;                 \
 454             slot || (slot = radix_tree_next_chunk(root, iter,          \
 455                              RADIX_TREE_ITER_TAGGED | tag)) ;          \
 456             slot = radix_tree_next_slot(slot, iter,                    \
 457                                RADIX_TREE_ITER_TAGGED))
 458
 459#endif /* _LINUX_RADIX_TREE_H */
 460
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