lib/radix-tree.c

   1 /*
   2  * Copyright (C) 2001 Momchil Velikov
   3  * Portions Copyright (C) 2001 Christoph Hellwig
   4  * Copyright (C) 2005 SGI, Christoph Lameter <clameter@sgi.com>
   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
  21 #include <linux/errno.h>
  22 #include <linux/init.h>
  23 #include <linux/kernel.h>
  24 #include <linux/module.h>
  25 #include <linux/radix-tree.h>
  26 #include <linux/percpu.h>
  27 #include <linux/slab.h>
  28 #include <linux/notifier.h>
  29 #include <linux/cpu.h>
  30 #include <linux/gfp.h>
  31 #include <linux/string.h>
  32 #include <linux/bitops.h>
  33
  34
  35 #ifdef __KERNEL__
  36 #define RADIX_TREE_MAP_SHIFT    (CONFIG_BASE_SMALL ? 4 : 6)
  37 #else
  38 #define RADIX_TREE_MAP_SHIFT    3       /* For more stressful testing */
  39 #endif
  40
  41 #define RADIX_TREE_MAP_SIZE     (1UL << RADIX_TREE_MAP_SHIFT)
  42 #define RADIX_TREE_MAP_MASK     (RADIX_TREE_MAP_SIZE-1)
  43
  44 #define RADIX_TREE_TAG_LONGS    \
  45         ((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)
  46
  47 struct radix_tree_node {
  48         unsigned int    count;
  49         void            *slots[RADIX_TREE_MAP_SIZE];
  50         unsigned long   tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
  51 };
  52
  53 struct radix_tree_path {
  54         struct radix_tree_node *node;
  55         int offset;
  56 };
  57
  58 #define RADIX_TREE_INDEX_BITS  (8 /* CHAR_BIT */ * sizeof(unsigned long))
  59 #define RADIX_TREE_MAX_PATH (RADIX_TREE_INDEX_BITS/RADIX_TREE_MAP_SHIFT + 2)
  60
  61 static unsigned long height_to_maxindex[RADIX_TREE_MAX_PATH] __read_mostly;
  62
  63 /*
  64  * Radix tree node cache.
  65  */
  66 static kmem_cache_t *radix_tree_node_cachep;
  67
  68 /*
  69  * Per-cpu pool of preloaded nodes
  70  */
  71 struct radix_tree_preload {
  72         int nr;
  73         struct radix_tree_node *nodes[RADIX_TREE_MAX_PATH];
  74 };
  75 DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
  76
  77 static inline gfp_t root_gfp_mask(struct radix_tree_root *root)
  78 {
  79         return root->gfp_mask & __GFP_BITS_MASK;
  80 }
  81
  82 /*
  83  * This assumes that the caller has performed appropriate preallocation, and
  84  * that the caller has pinned this thread of control to the current CPU.
  85  */
  86 static struct radix_tree_node *
  87 radix_tree_node_alloc(struct radix_tree_root *root)
  88 {
  89         struct radix_tree_node *ret;
  90         gfp_t gfp_mask = root_gfp_mask(root);
  91
  92         ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
  93         if (ret == NULL && !(gfp_mask & __GFP_WAIT)) {
  94                 struct radix_tree_preload *rtp;
  95
  96                 rtp = &__get_cpu_var(radix_tree_preloads);
  97                 if (rtp->nr) {
  98                         ret = rtp->nodes[rtp->nr - 1];
  99                         rtp->nodes[rtp->nr - 1] = NULL;
 100                         rtp->nr--;
 101                 }
 102         }
 103         return ret;
 104 }
 105
 106 static inline void
 107 radix_tree_node_free(struct radix_tree_node *node)
 108 {
 109         kmem_cache_free(radix_tree_node_cachep, node);
 110 }
 111
 112 /*
 113  * Load up this CPU's radix_tree_node buffer with sufficient objects to
 114  * ensure that the addition of a single element in the tree cannot fail.  On
 115  * success, return zero, with preemption disabled.  On error, return -ENOMEM
 116  * with preemption not disabled.
 117  */
 118 int radix_tree_preload(gfp_t gfp_mask)
 119 {
 120         struct radix_tree_preload *rtp;
 121         struct radix_tree_node *node;
 122         int ret = -ENOMEM;
 123
 124         preempt_disable();
 125         rtp = &__get_cpu_var(radix_tree_preloads);
 126         while (rtp->nr < ARRAY_SIZE(rtp->nodes)) {
 127                 preempt_enable();
 128                 node = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
 129                 if (node == NULL)
 130                         goto out;
 131                 preempt_disable();
 132                 rtp = &__get_cpu_var(radix_tree_preloads);
 133                 if (rtp->nr < ARRAY_SIZE(rtp->nodes))
 134                         rtp->nodes[rtp->nr++] = node;
 135                 else
 136                         kmem_cache_free(radix_tree_node_cachep, node);
 137         }
 138         ret = 0;
 139 out:
 140         return ret;
 141 }
 142
 143 static inline void tag_set(struct radix_tree_node *node, unsigned int tag,
 144                 int offset)
 145 {
 146         __set_bit(offset, node->tags[tag]);
 147 }
 148
 149 static inline void tag_clear(struct radix_tree_node *node, unsigned int tag,
 150                 int offset)
 151 {
 152         __clear_bit(offset, node->tags[tag]);
 153 }
 154
 155 static inline int tag_get(struct radix_tree_node *node, unsigned int tag,
 156                 int offset)
 157 {
 158         return test_bit(offset, node->tags[tag]);
 159 }
 160
 161 static inline void root_tag_set(struct radix_tree_root *root, unsigned int tag)
 162 {
 163         root->gfp_mask |= (__force gfp_t)(1 << (tag + __GFP_BITS_SHIFT));
 164 }
 165
 166
 167 static inline void root_tag_clear(struct radix_tree_root *root, unsigned int tag)
 168 {
 169         root->gfp_mask &= (__force gfp_t)~(1 << (tag + __GFP_BITS_SHIFT));
 170 }
 171
 172 static inline void root_tag_clear_all(struct radix_tree_root *root)
 173 {
 174         root->gfp_mask &= __GFP_BITS_MASK;
 175 }
 176
 177 static inline int root_tag_get(struct radix_tree_root *root, unsigned int tag)
 178 {
 179         return (__force unsigned)root->gfp_mask & (1 << (tag + __GFP_BITS_SHIFT));
 180 }
 181
 182 /*
 183  * Returns 1 if any slot in the node has this tag set.
 184  * Otherwise returns 0.
 185  */
 186 static inline int any_tag_set(struct radix_tree_node *node, unsigned int tag)
 187 {
 188         int idx;
 189         for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
 190                 if (node->tags[tag][idx])
 191                         return 1;
 192         }
 193         return 0;
 194 }
 195
 196 /*
 197  *      Return the maximum key which can be store into a
 198  *      radix tree with height HEIGHT.
 199  */
 200 static inline unsigned long radix_tree_maxindex(unsigned int height)
 201 {
 202         return height_to_maxindex[height];
 203 }
 204
 205 /*
 206  *      Extend a radix tree so it can store key @index.
 207  */
 208 static int radix_tree_extend(struct radix_tree_root *root, unsigned long index)
 209 {
 210         struct radix_tree_node *node;
 211         unsigned int height;
 212         int tag;
 213
 214         /* Figure out what the height should be.  */
 215         height = root->height + 1;
 216         while (index > radix_tree_maxindex(height))
 217                 height++;
 218
 219         if (root->rnode == NULL) {
 220                 root->height = height;
 221                 goto out;
 222         }
 223
 224         do {
 225                 if (!(node = radix_tree_node_alloc(root)))
 226                         return -ENOMEM;
 227
 228                 /* Increase the height.  */
 229                 node->slots[0] = root->rnode;
 230
 231                 /* Propagate the aggregated tag info into the new root */
 232                 for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
 233                         if (root_tag_get(root, tag))
 234                                 tag_set(node, tag, 0);
 235                 }
 236
 237                 node->count = 1;
 238                 root->rnode = node;
 239                 root->height++;
 240         } while (height > root->height);
 241 out:
 242         return 0;
 243 }
 244
 245 /**
 246  *      radix_tree_insert    -    insert into a radix tree
 247  *      @root:          radix tree root
 248  *      @index:         index key
 249  *      @item:          item to insert
 250  *
 251  *      Insert an item into the radix tree at position @index.
 252  */
 253 int radix_tree_insert(struct radix_tree_root *root,
 254                         unsigned long index, void *item)
 255 {
 256         struct radix_tree_node *node = NULL, *slot;
 257         unsigned int height, shift;
 258         int offset;
 259         int error;
 260
 261         /* Make sure the tree is high enough.  */
 262         if (index > radix_tree_maxindex(root->height)) {
 263                 error = radix_tree_extend(root, index);
 264                 if (error)
 265                         return error;
 266         }
 267
 268         slot = root->rnode;
 269         height = root->height;
 270         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
 271
 272         offset = 0;                     /* uninitialised var warning */
 273         while (height > 0) {
 274                 if (slot == NULL) {
 275                         /* Have to add a child node.  */
 276                         if (!(slot = radix_tree_node_alloc(root)))
 277                                 return -ENOMEM;
 278                         if (node) {
 279                                 node->slots[offset] = slot;
 280                                 node->count++;
 281                         } else
 282                                 root->rnode = slot;
 283                 }
 284
 285                 /* Go a level down */
 286                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 287                 node = slot;
 288                 slot = node->slots[offset];
 289                 shift -= RADIX_TREE_MAP_SHIFT;
 290                 height--;
 291         }
 292
 293         if (slot != NULL)
 294                 return -EEXIST;
 295
 296         if (node) {
 297                 node->count++;
 298                 node->slots[offset] = item;
 299                 BUG_ON(tag_get(node, 0, offset));
 300                 BUG_ON(tag_get(node, 1, offset));
 301         } else {
 302                 root->rnode = item;
 303                 BUG_ON(root_tag_get(root, 0));
 304                 BUG_ON(root_tag_get(root, 1));
 305         }
 306
 307         return 0;
 308 }
 309 EXPORT_SYMBOL(radix_tree_insert);
 310
 311 static inline void **__lookup_slot(struct radix_tree_root *root,
 312                                    unsigned long index)
 313 {
 314         unsigned int height, shift;
 315         struct radix_tree_node **slot;
 316
 317         height = root->height;
 318
 319         if (index > radix_tree_maxindex(height))
 320                 return NULL;
 321
 322         if (height == 0 && root->rnode)
 323                 return (void **)&root->rnode;
 324
 325         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
 326         slot = &root->rnode;
 327
 328         while (height > 0) {
 329                 if (*slot == NULL)
 330                         return NULL;
 331
 332                 slot = (struct radix_tree_node **)
 333                         ((*slot)->slots +
 334                                 ((index >> shift) & RADIX_TREE_MAP_MASK));
 335                 shift -= RADIX_TREE_MAP_SHIFT;
 336                 height--;
 337         }
 338
 339         return (void **)slot;
 340 }
 341
 342 /**
 343  *      radix_tree_lookup_slot    -    lookup a slot in a radix tree
 344  *      @root:          radix tree root
 345  *      @index:         index key
 346  *
 347  *      Lookup the slot corresponding to the position @index in the radix tree
 348  *      @root. This is useful for update-if-exists operations.
 349  */
 350 void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
 351 {
 352         return __lookup_slot(root, index);
 353 }
 354 EXPORT_SYMBOL(radix_tree_lookup_slot);
 355
 356 /**
 357  *      radix_tree_lookup    -    perform lookup operation on a radix tree
 358  *      @root:          radix tree root
 359  *      @index:         index key
 360  *
 361  *      Lookup the item at the position @index in the radix tree @root.
 362  */
 363 void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
 364 {
 365         void **slot;
 366
 367         slot = __lookup_slot(root, index);
 368         return slot != NULL ? *slot : NULL;
 369 }
 370 EXPORT_SYMBOL(radix_tree_lookup);
 371
 372 /**
 373  *      radix_tree_tag_set - set a tag on a radix tree node
 374  *      @root:          radix tree root
 375  *      @index:         index key
 376  *      @tag:           tag index
 377  *
 378  *      Set the search tag (which must be < RADIX_TREE_MAX_TAGS)
 379  *      corresponding to @index in the radix tree.  From
 380  *      the root all the way down to the leaf node.
 381  *
 382  *      Returns the address of the tagged item.   Setting a tag on a not-present
 383  *      item is a bug.
 384  */
 385 void *radix_tree_tag_set(struct radix_tree_root *root,
 386                         unsigned long index, unsigned int tag)
 387 {
 388         unsigned int height, shift;
 389         struct radix_tree_node *slot;
 390
 391         height = root->height;
 392         BUG_ON(index > radix_tree_maxindex(height));
 393
 394         slot = root->rnode;
 395         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 396
 397         while (height > 0) {
 398                 int offset;
 399
 400                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 401                 if (!tag_get(slot, tag, offset))
 402                         tag_set(slot, tag, offset);
 403                 slot = slot->slots[offset];
 404                 BUG_ON(slot == NULL);
 405                 shift -= RADIX_TREE_MAP_SHIFT;
 406                 height--;
 407         }
 408
 409         /* set the root's tag bit */
 410         if (slot && !root_tag_get(root, tag))
 411                 root_tag_set(root, tag);
 412
 413         return slot;
 414 }
 415 EXPORT_SYMBOL(radix_tree_tag_set);
 416
 417 /**
 418  *      radix_tree_tag_clear - clear a tag on a radix tree node
 419  *      @root:          radix tree root
 420  *      @index:         index key
 421  *      @tag:           tag index
 422  *
 423  *      Clear the search tag (which must be < RADIX_TREE_MAX_TAGS)
 424  *      corresponding to @index in the radix tree.  If
 425  *      this causes the leaf node to have no tags set then clear the tag in the
 426  *      next-to-leaf node, etc.
 427  *
 428  *      Returns the address of the tagged item on success, else NULL.  ie:
 429  *      has the same return value and semantics as radix_tree_lookup().
 430  */
 431 void *radix_tree_tag_clear(struct radix_tree_root *root,
 432                         unsigned long index, unsigned int tag)
 433 {
 434         struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;
 435         struct radix_tree_node *slot = NULL;
 436         unsigned int height, shift;
 437
 438         height = root->height;
 439         if (index > radix_tree_maxindex(height))
 440                 goto out;
 441
 442         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 443         pathp->node = NULL;
 444         slot = root->rnode;
 445
 446         while (height > 0) {
 447                 int offset;
 448
 449                 if (slot == NULL)
 450                         goto out;
 451
 452                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 453                 pathp[1].offset = offset;
 454                 pathp[1].node = slot;
 455                 slot = slot->slots[offset];
 456                 pathp++;
 457                 shift -= RADIX_TREE_MAP_SHIFT;
 458                 height--;
 459         }
 460
 461         if (slot == NULL)
 462                 goto out;
 463
 464         while (pathp->node) {
 465                 if (!tag_get(pathp->node, tag, pathp->offset))
 466                         goto out;
 467                 tag_clear(pathp->node, tag, pathp->offset);
 468                 if (any_tag_set(pathp->node, tag))
 469                         goto out;
 470                 pathp--;
 471         }
 472
 473         /* clear the root's tag bit */
 474         if (root_tag_get(root, tag))
 475                 root_tag_clear(root, tag);
 476
 477 out:
 478         return slot;
 479 }
 480 EXPORT_SYMBOL(radix_tree_tag_clear);
 481
 482 #ifndef __KERNEL__      /* Only the test harness uses this at present */
 483 /**
 484  * radix_tree_tag_get - get a tag on a radix tree node
 485  * @root:               radix tree root
 486  * @index:              index key
 487  * @tag:                tag index (< RADIX_TREE_MAX_TAGS)
 488  *
 489  * Return values:
 490  *
 491  *  0: tag not present or not set
 492  *  1: tag set
 493  */
 494 int radix_tree_tag_get(struct radix_tree_root *root,
 495                         unsigned long index, unsigned int tag)
 496 {
 497         unsigned int height, shift;
 498         struct radix_tree_node *slot;
 499         int saw_unset_tag = 0;
 500
 501         height = root->height;
 502         if (index > radix_tree_maxindex(height))
 503                 return 0;
 504
 505         /* check the root's tag bit */
 506         if (!root_tag_get(root, tag))
 507                 return 0;
 508
 509         if (height == 0)
 510                 return 1;
 511
 512         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 513         slot = root->rnode;
 514
 515         for ( ; ; ) {
 516                 int offset;
 517
 518                 if (slot == NULL)
 519                         return 0;
 520
 521                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 522
 523                 /*
 524                  * This is just a debug check.  Later, we can bale as soon as
 525                  * we see an unset tag.
 526                  */
 527                 if (!tag_get(slot, tag, offset))
 528                         saw_unset_tag = 1;
 529                 if (height == 1) {
 530                         int ret = tag_get(slot, tag, offset);
 531
 532                         BUG_ON(ret && saw_unset_tag);
 533                         return !!ret;
 534                 }
 535                 slot = slot->slots[offset];
 536                 shift -= RADIX_TREE_MAP_SHIFT;
 537                 height--;
 538         }
 539 }
 540 EXPORT_SYMBOL(radix_tree_tag_get);
 541 #endif
 542
 543 static unsigned int
 544 __lookup(struct radix_tree_root *root, void **results, unsigned long index,
 545         unsigned int max_items, unsigned long *next_index)
 546 {
 547         unsigned int nr_found = 0;
 548         unsigned int shift, height;
 549         struct radix_tree_node *slot;
 550         unsigned long i;
 551
 552         height = root->height;
 553         if (height == 0) {
 554                 if (root->rnode && index == 0)
 555                         results[nr_found++] = root->rnode;
 556                 goto out;
 557         }
 558
 559         shift = (height-1) * RADIX_TREE_MAP_SHIFT;
 560         slot = root->rnode;
 561
 562         for ( ; height > 1; height--) {
 563
 564                 for (i = (index >> shift) & RADIX_TREE_MAP_MASK ;
 565                                 i < RADIX_TREE_MAP_SIZE; i++) {
 566                         if (slot->slots[i] != NULL)
 567                                 break;
 568                         index &= ~((1UL << shift) - 1);
 569                         index += 1UL << shift;
 570                         if (index == 0)
 571                                 goto out;       /* 32-bit wraparound */
 572                 }
 573                 if (i == RADIX_TREE_MAP_SIZE)
 574                         goto out;
 575
 576                 shift -= RADIX_TREE_MAP_SHIFT;
 577                 slot = slot->slots[i];
 578         }
 579
 580         /* Bottom level: grab some items */
 581         for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++) {
 582                 index++;
 583                 if (slot->slots[i]) {
 584                         results[nr_found++] = slot->slots[i];
 585                         if (nr_found == max_items)
 586                                 goto out;
 587                 }
 588         }
 589 out:
 590         *next_index = index;
 591         return nr_found;
 592 }
 593
 594 /**
 595  *      radix_tree_gang_lookup - perform multiple lookup on a radix tree
 596  *      @root:          radix tree root
 597  *      @results:       where the results of the lookup are placed
 598  *      @first_index:   start the lookup from this key
 599  *      @max_items:     place up to this many items at *results
 600  *
 601  *      Performs an index-ascending scan of the tree for present items.  Places
 602  *      them at *@results and returns the number of items which were placed at
 603  *      *@results.
 604  *
 605  *      The implementation is naive.
 606  */
 607 unsigned int
 608 radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
 609                         unsigned long first_index, unsigned int max_items)
 610 {
 611         const unsigned long max_index = radix_tree_maxindex(root->height);
 612         unsigned long cur_index = first_index;
 613         unsigned int ret = 0;
 614
 615         while (ret < max_items) {
 616                 unsigned int nr_found;
 617                 unsigned long next_index;       /* Index of next search */
 618
 619                 if (cur_index > max_index)
 620                         break;
 621                 nr_found = __lookup(root, results + ret, cur_index,
 622                                         max_items - ret, &next_index);
 623                 ret += nr_found;
 624                 if (next_index == 0)
 625                         break;
 626                 cur_index = next_index;
 627         }
 628         return ret;
 629 }
 630 EXPORT_SYMBOL(radix_tree_gang_lookup);
 631
 632 /*
 633  * FIXME: the two tag_get()s here should use find_next_bit() instead of
 634  * open-coding the search.
 635  */
 636 static unsigned int
 637 __lookup_tag(struct radix_tree_root *root, void **results, unsigned long index,
 638         unsigned int max_items, unsigned long *next_index, unsigned int tag)
 639 {
 640         unsigned int nr_found = 0;
 641         unsigned int shift;
 642         unsigned int height = root->height;
 643         struct radix_tree_node *slot;
 644
 645         if (height == 0) {
 646                 if (root->rnode && index == 0)
 647                         results[nr_found++] = root->rnode;
 648                 goto out;
 649         }
 650
 651         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 652         slot = root->rnode;
 653
 654         do {
 655                 unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK;
 656
 657                 for ( ; i < RADIX_TREE_MAP_SIZE; i++) {
 658                         if (tag_get(slot, tag, i)) {
 659                                 BUG_ON(slot->slots[i] == NULL);
 660                                 break;
 661                         }
 662                         index &= ~((1UL << shift) - 1);
 663                         index += 1UL << shift;
 664                         if (index == 0)
 665                                 goto out;       /* 32-bit wraparound */
 666                 }
 667                 if (i == RADIX_TREE_MAP_SIZE)
 668                         goto out;
 669                 height--;
 670                 if (height == 0) {      /* Bottom level: grab some items */
 671                         unsigned long j = index & RADIX_TREE_MAP_MASK;
 672
 673                         for ( ; j < RADIX_TREE_MAP_SIZE; j++) {
 674                                 index++;
 675                                 if (tag_get(slot, tag, j)) {
 676                                         BUG_ON(slot->slots[j] == NULL);
 677                                         results[nr_found++] = slot->slots[j];
 678                                         if (nr_found == max_items)
 679                                                 goto out;
 680                                 }
 681                         }
 682                 }
 683                 shift -= RADIX_TREE_MAP_SHIFT;
 684                 slot = slot->slots[i];
 685         } while (height > 0);
 686 out:
 687         *next_index = index;
 688         return nr_found;
 689 }
 690
 691 /**
 692  *      radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
 693  *                                   based on a tag
 694  *      @root:          radix tree root
 695  *      @results:       where the results of the lookup are placed
 696  *      @first_index:   start the lookup from this key
 697  *      @max_items:     place up to this many items at *results
 698  *      @tag:           the tag index (< RADIX_TREE_MAX_TAGS)
 699  *
 700  *      Performs an index-ascending scan of the tree for present items which
 701  *      have the tag indexed by @tag set.  Places the items at *@results and
 702  *      returns the number of items which were placed at *@results.
 703  */
 704 unsigned int
 705 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
 706                 unsigned long first_index, unsigned int max_items,
 707                 unsigned int tag)
 708 {
 709         const unsigned long max_index = radix_tree_maxindex(root->height);
 710         unsigned long cur_index = first_index;
 711         unsigned int ret = 0;
 712
 713         /* check the root's tag bit */
 714         if (!root_tag_get(root, tag))
 715                 return 0;
 716
 717         while (ret < max_items) {
 718                 unsigned int nr_found;
 719                 unsigned long next_index;       /* Index of next search */
 720
 721                 if (cur_index > max_index)
 722                         break;
 723                 nr_found = __lookup_tag(root, results + ret, cur_index,
 724                                         max_items - ret, &next_index, tag);
 725                 ret += nr_found;
 726                 if (next_index == 0)
 727                         break;
 728                 cur_index = next_index;
 729         }
 730         return ret;
 731 }
 732 EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
 733
 734 /**
 735  *      radix_tree_shrink    -    shrink height of a radix tree to minimal
 736  *      @root           radix tree root
 737  */
 738 static inline void radix_tree_shrink(struct radix_tree_root *root)
 739 {
 740         /* try to shrink tree height */
 741         while (root->height > 0 &&
 742                         root->rnode->count == 1 &&
 743                         root->rnode->slots[0]) {
 744                 struct radix_tree_node *to_free = root->rnode;
 745
 746                 root->rnode = to_free->slots[0];
 747                 root->height--;
 748                 /* must only free zeroed nodes into the slab */
 749                 tag_clear(to_free, 0, 0);
 750                 tag_clear(to_free, 1, 0);
 751                 to_free->slots[0] = NULL;
 752                 to_free->count = 0;
 753                 radix_tree_node_free(to_free);
 754         }
 755 }
 756
 757 /**
 758  *      radix_tree_delete    -    delete an item from a radix tree
 759  *      @root:          radix tree root
 760  *      @index:         index key
 761  *
 762  *      Remove the item at @index from the radix tree rooted at @root.
 763  *
 764  *      Returns the address of the deleted item, or NULL if it was not present.
 765  */
 766 void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
 767 {
 768         struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;
 769         struct radix_tree_node *slot = NULL;
 770         unsigned int height, shift;
 771         int tag;
 772         int offset;
 773
 774         height = root->height;
 775         if (index > radix_tree_maxindex(height))
 776                 goto out;
 777
 778         slot = root->rnode;
 779         if (height == 0 && root->rnode) {
 780                 root_tag_clear_all(root);
 781                 root->rnode = NULL;
 782                 goto out;
 783         }
 784
 785         shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 786         pathp->node = NULL;
 787
 788         do {
 789                 if (slot == NULL)
 790                         goto out;
 791
 792                 pathp++;
 793                 offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 794                 pathp->offset = offset;
 795                 pathp->node = slot;
 796                 slot = slot->slots[offset];
 797                 shift -= RADIX_TREE_MAP_SHIFT;
 798                 height--;
 799         } while (height > 0);
 800
 801         if (slot == NULL)
 802                 goto out;
 803
 804         /*
 805          * Clear all tags associated with the just-deleted item
 806          */
 807         for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
 808                 if (tag_get(pathp->node, tag, pathp->offset))
 809                         radix_tree_tag_clear(root, index, tag);
 810         }
 811
 812         /* Now free the nodes we do not need anymore */
 813         while (pathp->node) {
 814                 pathp->node->slots[pathp->offset] = NULL;
 815                 pathp->node->count--;
 816
 817                 if (pathp->node->count) {
 818                         if (pathp->node == root->rnode)
 819                                 radix_tree_shrink(root);
 820                         goto out;
 821                 }
 822
 823                 /* Node with zero slots in use so free it */
 824                 radix_tree_node_free(pathp->node);
 825
 826                 pathp--;
 827         }
 828         root_tag_clear_all(root);
 829         root->height = 0;
 830         root->rnode = NULL;
 831
 832 out:
 833         return slot;
 834 }
 835 EXPORT_SYMBOL(radix_tree_delete);
 836
 837 /**
 838  *      radix_tree_tagged - test whether any items in the tree are tagged
 839  *      @root:          radix tree root
 840  *      @tag:           tag to test
 841  */
 842 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag)
 843 {
 844         return root_tag_get(root, tag);
 845 }
 846 EXPORT_SYMBOL(radix_tree_tagged);
 847
 848 static void
 849 radix_tree_node_ctor(void *node, kmem_cache_t *cachep, unsigned long flags)
 850 {
 851         memset(node, 0, sizeof(struct radix_tree_node));
 852 }
 853
 854 static __init unsigned long __maxindex(unsigned int height)
 855 {
 856         unsigned int tmp = height * RADIX_TREE_MAP_SHIFT;
 857         unsigned long index = (~0UL >> (RADIX_TREE_INDEX_BITS - tmp - 1)) >> 1;
 858
 859         if (tmp >= RADIX_TREE_INDEX_BITS)
 860                 index = ~0UL;
 861         return index;
 862 }
 863
 864 static __init void radix_tree_init_maxindex(void)
 865 {
 866         unsigned int i;
 867
 868         for (i = 0; i < ARRAY_SIZE(height_to_maxindex); i++)
 869                 height_to_maxindex[i] = __maxindex(i);
 870 }
 871
 872 #ifdef CONFIG_HOTPLUG_CPU
 873 static int radix_tree_callback(struct notifier_block *nfb,
 874                             unsigned long action,
 875                             void *hcpu)
 876 {
 877        int cpu = (long)hcpu;
 878        struct radix_tree_preload *rtp;
 879
 880        /* Free per-cpu pool of perloaded nodes */
 881        if (action == CPU_DEAD) {
 882                rtp = &per_cpu(radix_tree_preloads, cpu);
 883                while (rtp->nr) {
 884                        kmem_cache_free(radix_tree_node_cachep,
 885                                        rtp->nodes[rtp->nr-1]);
 886                        rtp->nodes[rtp->nr-1] = NULL;
 887                        rtp->nr--;
 888                }
 889        }
 890        return NOTIFY_OK;
 891 }
 892 #endif /* CONFIG_HOTPLUG_CPU */
 893
 894 void __init radix_tree_init(void)
 895 {
 896         radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
 897                         sizeof(struct radix_tree_node), 0,
 898                         SLAB_PANIC, radix_tree_node_ctor, NULL);
 899         radix_tree_init_maxindex();
 900         hotcpu_notifier(radix_tree_callback, 0);
 901 }