root/fs/befs/btree.c

DEFINITIONS

1. befs_bt_read_super
2. befs_bt_read_node
3. befs_btree_find
4. befs_find_key
5. befs_btree_read
6. befs_btree_seekleaf
7. befs_leafnode
8. befs_bt_keylen_index
9. befs_bt_valarray
10. befs_bt_keydata
11. befs_bt_get_key
12. befs_compare_strings
13. btree_compare_int32
14. btree_compare_uint32
15. btree_compare_int64
16. btree_compare_uint64
17. btree_compare_float
18. btree_compare_double

   1 /*
   2  * linux/fs/befs/btree.c
   3  *
   4  * Copyright (C) 2001-2002 Will Dyson <will_dyson@pobox.com>
   5  *
   6  * Licensed under the GNU GPL. See the file COPYING for details.
   7  *
   8  * 2002-02-05: Sergey S. Kostyliov added binary search within
   9  *              btree nodes.
  10  *
  11  * Many thanks to:
  12  *
  13  * Dominic Giampaolo, author of "Practical File System
  14  * Design with the Be File System", for such a helpful book.
  15  *
  16  * Marcus J. Ranum, author of the b+tree package in
  17  * comp.sources.misc volume 10. This code is not copied from that
  18  * work, but it is partially based on it.
  19  *
  20  * Makoto Kato, author of the original BeFS for linux filesystem
  21  * driver.
  22  */
  23 
  24 #include <linux/kernel.h>
  25 #include <linux/string.h>
  26 #include <linux/slab.h>
  27 #include <linux/mm.h>
  28 #include <linux/buffer_head.h>
  29 
  30 #include "befs.h"
  31 #include "btree.h"
  32 #include "datastream.h"
  33 
  34 /*
  35  * The btree functions in this file are built on top of the
  36  * datastream.c interface, which is in turn built on top of the
  37  * io.c interface.
  38  */
  39 
  40 /* Befs B+tree structure:
  41  *
  42  * The first thing in the tree is the tree superblock. It tells you
  43  * all kinds of useful things about the tree, like where the rootnode
  44  * is located, and the size of the nodes (always 1024 with current version
  45  * of BeOS).
  46  *
  47  * The rest of the tree consists of a series of nodes. Nodes contain a header
  48  * (struct befs_btree_nodehead), the packed key data, an array of shorts
  49  * containing the ending offsets for each of the keys, and an array of
  50  * befs_off_t values. In interior nodes, the keys are the ending keys for
  51  * the childnode they point to, and the values are offsets into the
  52  * datastream containing the tree.
  53  */
  54 
  55 /* Note:
  56  *
  57  * The book states 2 confusing things about befs b+trees. First,
  58  * it states that the overflow field of node headers is used by internal nodes
  59  * to point to another node that "effectively continues this one". Here is what
  60  * I believe that means. Each key in internal nodes points to another node that
  61  * contains key values less than itself. Inspection reveals that the last key
  62  * in the internal node is not the last key in the index. Keys that are
  63  * greater than the last key in the internal node go into the overflow node.
  64  * I imagine there is a performance reason for this.
  65  *
  66  * Second, it states that the header of a btree node is sufficient to
  67  * distinguish internal nodes from leaf nodes. Without saying exactly how.
  68  * After figuring out the first, it becomes obvious that internal nodes have
  69  * overflow nodes and leafnodes do not.
  70  */
  71 
  72 /*
  73  * Currently, this code is only good for directory B+trees.
  74  * In order to be used for other BFS indexes, it needs to be extended to handle
  75  * duplicate keys and non-string keytypes (int32, int64, float, double).
  76  */
  77 
  78 /*
  79  * In memory structure of each btree node
  80  */
  81 struct befs_btree_node {
  82         befs_host_btree_nodehead head;  /* head of node converted to cpu byteorder */
  83         struct buffer_head *bh;
  84         befs_btree_nodehead *od_node;   /* on disk node */
  85 };
  86 
  87 /* local constants */
  88 static const befs_off_t BEFS_BT_INVAL = 0xffffffffffffffffULL;
  89 
  90 /* local functions */
  91 static int befs_btree_seekleaf(struct super_block *sb, const befs_data_stream *ds,
  92                                befs_btree_super * bt_super,
  93                                struct befs_btree_node *this_node,
  94                                befs_off_t * node_off);
  95 
  96 static int befs_bt_read_super(struct super_block *sb, const befs_data_stream *ds,
  97                               befs_btree_super * sup);
  98 
  99 static int befs_bt_read_node(struct super_block *sb, const befs_data_stream *ds,
 100                              struct befs_btree_node *node,
 101                              befs_off_t node_off);
 102 
 103 static int befs_leafnode(struct befs_btree_node *node);
 104 
 105 static fs16 *befs_bt_keylen_index(struct befs_btree_node *node);
 106 
 107 static fs64 *befs_bt_valarray(struct befs_btree_node *node);
 108 
 109 static char *befs_bt_keydata(struct befs_btree_node *node);
 110 
 111 static int befs_find_key(struct super_block *sb,
 112                          struct befs_btree_node *node,
 113                          const char *findkey, befs_off_t * value);
 114 
 115 static char *befs_bt_get_key(struct super_block *sb,
 116                              struct befs_btree_node *node,
 117                              int index, u16 * keylen);
 118 
 119 static int befs_compare_strings(const void *key1, int keylen1,
 120                                 const void *key2, int keylen2);
 121 
 122 /**
 123  * befs_bt_read_super() - read in btree superblock convert to cpu byteorder
 124  * @sb:        Filesystem superblock
 125  * @ds:        Datastream to read from
 126  * @sup:       Buffer in which to place the btree superblock
 127  *
 128  * Calls befs_read_datastream to read in the btree superblock and
 129  * makes sure it is in cpu byteorder, byteswapping if necessary.
 130  * Return: BEFS_OK on success and if *@sup contains the btree superblock in cpu
 131  * byte order. Otherwise return BEFS_ERR on error.
 132  */
 133 static int
 134 befs_bt_read_super(struct super_block *sb, const befs_data_stream *ds,
 135                    befs_btree_super * sup)
 136 {
 137         struct buffer_head *bh;
 138         befs_disk_btree_super *od_sup;
 139 
 140         befs_debug(sb, "---> %s", __func__);
 141 
 142         bh = befs_read_datastream(sb, ds, 0, NULL);
 143 
 144         if (!bh) {
 145                 befs_error(sb, "Couldn't read index header.");
 146                 goto error;
 147         }
 148         od_sup = (befs_disk_btree_super *) bh->b_data;
 149         befs_dump_index_entry(sb, od_sup);
 150 
 151         sup->magic = fs32_to_cpu(sb, od_sup->magic);
 152         sup->node_size = fs32_to_cpu(sb, od_sup->node_size);
 153         sup->max_depth = fs32_to_cpu(sb, od_sup->max_depth);
 154         sup->data_type = fs32_to_cpu(sb, od_sup->data_type);
 155         sup->root_node_ptr = fs64_to_cpu(sb, od_sup->root_node_ptr);
 156 
 157         brelse(bh);
 158         if (sup->magic != BEFS_BTREE_MAGIC) {
 159                 befs_error(sb, "Index header has bad magic.");
 160                 goto error;
 161         }
 162 
 163         befs_debug(sb, "<--- %s", __func__);
 164         return BEFS_OK;
 165 
 166       error:
 167         befs_debug(sb, "<--- %s ERROR", __func__);
 168         return BEFS_ERR;
 169 }
 170 
 171 /**
 172  * befs_bt_read_node - read in btree node and convert to cpu byteorder
 173  * @sb: Filesystem superblock
 174  * @ds: Datastream to read from
 175  * @node: Buffer in which to place the btree node
 176  * @node_off: Starting offset (in bytes) of the node in @ds
 177  *
 178  * Calls befs_read_datastream to read in the indicated btree node and
 179  * makes sure its header fields are in cpu byteorder, byteswapping if
 180  * necessary.
 181  * Note: node->bh must be NULL when this function is called the first time.
 182  * Don't forget brelse(node->bh) after last call.
 183  *
 184  * On success, returns BEFS_OK and *@node contains the btree node that
 185  * starts at @node_off, with the node->head fields in cpu byte order.
 186  *
 187  * On failure, BEFS_ERR is returned.
 188  */
 189 
 190 static int
 191 befs_bt_read_node(struct super_block *sb, const befs_data_stream *ds,
 192                   struct befs_btree_node *node, befs_off_t node_off)
 193 {
 194         uint off = 0;
 195 
 196         befs_debug(sb, "---> %s", __func__);
 197 
 198         if (node->bh)
 199                 brelse(node->bh);
 200 
 201         node->bh = befs_read_datastream(sb, ds, node_off, &off);
 202         if (!node->bh) {
 203                 befs_error(sb, "%s failed to read "
 204                            "node at %llu", __func__, node_off);
 205                 befs_debug(sb, "<--- %s ERROR", __func__);
 206 
 207                 return BEFS_ERR;
 208         }
 209         node->od_node =
 210             (befs_btree_nodehead *) ((void *) node->bh->b_data + off);
 211 
 212         befs_dump_index_node(sb, node->od_node);
 213 
 214         node->head.left = fs64_to_cpu(sb, node->od_node->left);
 215         node->head.right = fs64_to_cpu(sb, node->od_node->right);
 216         node->head.overflow = fs64_to_cpu(sb, node->od_node->overflow);
 217         node->head.all_key_count =
 218             fs16_to_cpu(sb, node->od_node->all_key_count);
 219         node->head.all_key_length =
 220             fs16_to_cpu(sb, node->od_node->all_key_length);
 221 
 222         befs_debug(sb, "<--- %s", __func__);
 223         return BEFS_OK;
 224 }
 225 
 226 /**
 227  * befs_btree_find - Find a key in a befs B+tree
 228  * @sb: Filesystem superblock
 229  * @ds: Datastream containing btree
 230  * @key: Key string to lookup in btree
 231  * @value: Value stored with @key
 232  *
 233  * On success, returns BEFS_OK and sets *@value to the value stored
 234  * with @key (usually the disk block number of an inode).
 235  *
 236  * On failure, returns BEFS_ERR or BEFS_BT_NOT_FOUND.
 237  *
 238  * Algorithm:
 239  *   Read the superblock and rootnode of the b+tree.
 240  *   Drill down through the interior nodes using befs_find_key().
 241  *   Once at the correct leaf node, use befs_find_key() again to get the
 242  *   actual value stored with the key.
 243  */
 244 int
 245 befs_btree_find(struct super_block *sb, const befs_data_stream *ds,
 246                 const char *key, befs_off_t * value)
 247 {
 248         struct befs_btree_node *this_node;
 249         befs_btree_super bt_super;
 250         befs_off_t node_off;
 251         int res;
 252 
 253         befs_debug(sb, "---> %s Key: %s", __func__, key);
 254 
 255         if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {
 256                 befs_error(sb,
 257                            "befs_btree_find() failed to read index superblock");
 258                 goto error;
 259         }
 260 
 261         this_node = kmalloc(sizeof(struct befs_btree_node),
 262                                                 GFP_NOFS);
 263         if (!this_node) {
 264                 befs_error(sb, "befs_btree_find() failed to allocate %zu "
 265                            "bytes of memory", sizeof(struct befs_btree_node));
 266                 goto error;
 267         }
 268 
 269         this_node->bh = NULL;
 270 
 271         /* read in root node */
 272         node_off = bt_super.root_node_ptr;
 273         if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
 274                 befs_error(sb, "befs_btree_find() failed to read "
 275                            "node at %llu", node_off);
 276                 goto error_alloc;
 277         }
 278 
 279         while (!befs_leafnode(this_node)) {
 280                 res = befs_find_key(sb, this_node, key, &node_off);
 281                 /* if no key set, try the overflow node */
 282                 if (res == BEFS_BT_OVERFLOW)
 283                         node_off = this_node->head.overflow;
 284                 if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
 285                         befs_error(sb, "befs_btree_find() failed to read "
 286                                    "node at %llu", node_off);
 287                         goto error_alloc;
 288                 }
 289         }
 290 
 291         /* at a leaf node now, check if it is correct */
 292         res = befs_find_key(sb, this_node, key, value);
 293 
 294         brelse(this_node->bh);
 295         kfree(this_node);
 296 
 297         if (res != BEFS_BT_MATCH) {
 298                 befs_error(sb, "<--- %s Key %s not found", __func__, key);
 299                 befs_debug(sb, "<--- %s ERROR", __func__);
 300                 *value = 0;
 301                 return BEFS_BT_NOT_FOUND;
 302         }
 303         befs_debug(sb, "<--- %s Found key %s, value %llu", __func__,
 304                    key, *value);
 305         return BEFS_OK;
 306 
 307       error_alloc:
 308         kfree(this_node);
 309       error:
 310         *value = 0;
 311         befs_debug(sb, "<--- %s ERROR", __func__);
 312         return BEFS_ERR;
 313 }
 314 
 315 /**
 316  * befs_find_key - Search for a key within a node
 317  * @sb: Filesystem superblock
 318  * @node: Node to find the key within
 319  * @findkey: Keystring to search for
 320  * @value: If key is found, the value stored with the key is put here
 321  *
 322  * Finds exact match if one exists, and returns BEFS_BT_MATCH.
 323  * If there is no match and node's value array is too small for key, return
 324  * BEFS_BT_OVERFLOW.
 325  * If no match and node should countain this key, return BEFS_BT_NOT_FOUND.
 326  *
 327  * Uses binary search instead of a linear.
 328  */
 329 static int
 330 befs_find_key(struct super_block *sb, struct befs_btree_node *node,
 331               const char *findkey, befs_off_t * value)
 332 {
 333         int first, last, mid;
 334         int eq;
 335         u16 keylen;
 336         int findkey_len;
 337         char *thiskey;
 338         fs64 *valarray;
 339 
 340         befs_debug(sb, "---> %s %s", __func__, findkey);
 341 
 342         findkey_len = strlen(findkey);
 343 
 344         /* if node can not contain key, just skip this node */
 345         last = node->head.all_key_count - 1;
 346         thiskey = befs_bt_get_key(sb, node, last, &keylen);
 347 
 348         eq = befs_compare_strings(thiskey, keylen, findkey, findkey_len);
 349         if (eq < 0) {
 350                 befs_debug(sb, "<--- node can't contain %s", findkey);
 351                 return BEFS_BT_OVERFLOW;
 352         }
 353 
 354         valarray = befs_bt_valarray(node);
 355 
 356         /* simple binary search */
 357         first = 0;
 358         mid = 0;
 359         while (last >= first) {
 360                 mid = (last + first) / 2;
 361                 befs_debug(sb, "first: %d, last: %d, mid: %d", first, last,
 362                            mid);
 363                 thiskey = befs_bt_get_key(sb, node, mid, &keylen);
 364                 eq = befs_compare_strings(thiskey, keylen, findkey,
 365                                           findkey_len);
 366 
 367                 if (eq == 0) {
 368                         befs_debug(sb, "<--- %s found %s at %d",
 369                                    __func__, thiskey, mid);
 370 
 371                         *value = fs64_to_cpu(sb, valarray[mid]);
 372                         return BEFS_BT_MATCH;
 373                 }
 374                 if (eq > 0)
 375                         last = mid - 1;
 376                 else
 377                         first = mid + 1;
 378         }
 379 
 380         /* return an existing value so caller can arrive to a leaf node */
 381         if (eq < 0)
 382                 *value = fs64_to_cpu(sb, valarray[mid + 1]);
 383         else
 384                 *value = fs64_to_cpu(sb, valarray[mid]);
 385         befs_error(sb, "<--- %s %s not found", __func__, findkey);
 386         befs_debug(sb, "<--- %s ERROR", __func__);
 387         return BEFS_BT_NOT_FOUND;
 388 }
 389 
 390 /**
 391  * befs_btree_read - Traverse leafnodes of a btree
 392  * @sb: Filesystem superblock
 393  * @ds: Datastream containing btree
 394  * @key_no: Key number (alphabetical order) of key to read
 395  * @bufsize: Size of the buffer to return key in
 396  * @keybuf: Pointer to a buffer to put the key in
 397  * @keysize: Length of the returned key
 398  * @value: Value stored with the returned key
 399  *
 400  * Here's how it works: Key_no is the index of the key/value pair to
 401  * return in keybuf/value.
 402  * Bufsize is the size of keybuf (BEFS_NAME_LEN+1 is a good size). Keysize is
 403  * the number of characters in the key (just a convenience).
 404  *
 405  * Algorithm:
 406  *   Get the first leafnode of the tree. See if the requested key is in that
 407  *   node. If not, follow the node->right link to the next leafnode. Repeat
 408  *   until the (key_no)th key is found or the tree is out of keys.
 409  */
 410 int
 411 befs_btree_read(struct super_block *sb, const befs_data_stream *ds,
 412                 loff_t key_no, size_t bufsize, char *keybuf, size_t * keysize,
 413                 befs_off_t * value)
 414 {
 415         struct befs_btree_node *this_node;
 416         befs_btree_super bt_super;
 417         befs_off_t node_off;
 418         int cur_key;
 419         fs64 *valarray;
 420         char *keystart;
 421         u16 keylen;
 422         int res;
 423 
 424         uint key_sum = 0;
 425 
 426         befs_debug(sb, "---> %s", __func__);
 427 
 428         if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {
 429                 befs_error(sb,
 430                            "befs_btree_read() failed to read index superblock");
 431                 goto error;
 432         }
 433 
 434         this_node = kmalloc(sizeof(struct befs_btree_node), GFP_NOFS);
 435         if (this_node == NULL) {
 436                 befs_error(sb, "befs_btree_read() failed to allocate %zu "
 437                            "bytes of memory", sizeof(struct befs_btree_node));
 438                 goto error;
 439         }
 440 
 441         node_off = bt_super.root_node_ptr;
 442         this_node->bh = NULL;
 443 
 444         /* seeks down to first leafnode, reads it into this_node */
 445         res = befs_btree_seekleaf(sb, ds, &bt_super, this_node, &node_off);
 446         if (res == BEFS_BT_EMPTY) {
 447                 brelse(this_node->bh);
 448                 kfree(this_node);
 449                 *value = 0;
 450                 *keysize = 0;
 451                 befs_debug(sb, "<--- %s Tree is EMPTY", __func__);
 452                 return BEFS_BT_EMPTY;
 453         } else if (res == BEFS_ERR) {
 454                 goto error_alloc;
 455         }
 456 
 457         /* find the leaf node containing the key_no key */
 458 
 459         while (key_sum + this_node->head.all_key_count <= key_no) {
 460 
 461                 /* no more nodes to look in: key_no is too large */
 462                 if (this_node->head.right == BEFS_BT_INVAL) {
 463                         *keysize = 0;
 464                         *value = 0;
 465                         befs_debug(sb,
 466                                    "<--- %s END of keys at %llu", __func__,
 467                                    (unsigned long long)
 468                                    key_sum + this_node->head.all_key_count);
 469                         brelse(this_node->bh);
 470                         kfree(this_node);
 471                         return BEFS_BT_END;
 472                 }
 473 
 474                 key_sum += this_node->head.all_key_count;
 475                 node_off = this_node->head.right;
 476 
 477                 if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
 478                         befs_error(sb, "%s failed to read node at %llu",
 479                                   __func__, (unsigned long long)node_off);
 480                         goto error_alloc;
 481                 }
 482         }
 483 
 484         /* how many keys into this_node is key_no */
 485         cur_key = key_no - key_sum;
 486 
 487         /* get pointers to datastructures within the node body */
 488         valarray = befs_bt_valarray(this_node);
 489 
 490         keystart = befs_bt_get_key(sb, this_node, cur_key, &keylen);
 491 
 492         befs_debug(sb, "Read [%llu,%d]: keysize %d",
 493                    (long long unsigned int)node_off, (int)cur_key,
 494                    (int)keylen);
 495 
 496         if (bufsize < keylen + 1) {
 497                 befs_error(sb, "%s keybuf too small (%zu) "
 498                            "for key of size %d", __func__, bufsize, keylen);
 499                 brelse(this_node->bh);
 500                 goto error_alloc;
 501         }
 502 
 503         strlcpy(keybuf, keystart, keylen + 1);
 504         *value = fs64_to_cpu(sb, valarray[cur_key]);
 505         *keysize = keylen;
 506 
 507         befs_debug(sb, "Read [%llu,%d]: Key \"%.*s\", Value %llu", node_off,
 508                    cur_key, keylen, keybuf, *value);
 509 
 510         brelse(this_node->bh);
 511         kfree(this_node);
 512 
 513         befs_debug(sb, "<--- %s", __func__);
 514 
 515         return BEFS_OK;
 516 
 517       error_alloc:
 518         kfree(this_node);
 519 
 520       error:
 521         *keysize = 0;
 522         *value = 0;
 523         befs_debug(sb, "<--- %s ERROR", __func__);
 524         return BEFS_ERR;
 525 }
 526 
 527 /**
 528  * befs_btree_seekleaf - Find the first leafnode in the btree
 529  * @sb: Filesystem superblock
 530  * @ds: Datastream containing btree
 531  * @bt_super: Pointer to the superblock of the btree
 532  * @this_node: Buffer to return the leafnode in
 533  * @node_off: Pointer to offset of current node within datastream. Modified
 534  *              by the function.
 535  *
 536  * Helper function for btree traverse. Moves the current position to the
 537  * start of the first leaf node.
 538  *
 539  * Also checks for an empty tree. If there are no keys, returns BEFS_BT_EMPTY.
 540  */
 541 static int
 542 befs_btree_seekleaf(struct super_block *sb, const befs_data_stream *ds,
 543                     befs_btree_super *bt_super,
 544                     struct befs_btree_node *this_node,
 545                     befs_off_t * node_off)
 546 {
 547 
 548         befs_debug(sb, "---> %s", __func__);
 549 
 550         if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
 551                 befs_error(sb, "%s failed to read "
 552                            "node at %llu", __func__, *node_off);
 553                 goto error;
 554         }
 555         befs_debug(sb, "Seekleaf to root node %llu", *node_off);
 556 
 557         if (this_node->head.all_key_count == 0 && befs_leafnode(this_node)) {
 558                 befs_debug(sb, "<--- %s Tree is EMPTY", __func__);
 559                 return BEFS_BT_EMPTY;
 560         }
 561 
 562         while (!befs_leafnode(this_node)) {
 563 
 564                 if (this_node->head.all_key_count == 0) {
 565                         befs_debug(sb, "%s encountered "
 566                                    "an empty interior node: %llu. Using Overflow "
 567                                    "node: %llu", __func__, *node_off,
 568                                    this_node->head.overflow);
 569                         *node_off = this_node->head.overflow;
 570                 } else {
 571                         fs64 *valarray = befs_bt_valarray(this_node);
 572                         *node_off = fs64_to_cpu(sb, valarray[0]);
 573                 }
 574                 if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
 575                         befs_error(sb, "%s failed to read "
 576                                    "node at %llu", __func__, *node_off);
 577                         goto error;
 578                 }
 579 
 580                 befs_debug(sb, "Seekleaf to child node %llu", *node_off);
 581         }
 582         befs_debug(sb, "Node %llu is a leaf node", *node_off);
 583 
 584         return BEFS_OK;
 585 
 586       error:
 587         befs_debug(sb, "<--- %s ERROR", __func__);
 588         return BEFS_ERR;
 589 }
 590 
 591 /**
 592  * befs_leafnode - Determine if the btree node is a leaf node or an
 593  * interior node
 594  * @node: Pointer to node structure to test
 595  *
 596  * Return 1 if leaf, 0 if interior
 597  */
 598 static int
 599 befs_leafnode(struct befs_btree_node *node)
 600 {
 601         /* all interior nodes (and only interior nodes) have an overflow node */
 602         if (node->head.overflow == BEFS_BT_INVAL)
 603                 return 1;
 604         else
 605                 return 0;
 606 }
 607 
 608 /**
 609  * befs_bt_keylen_index - Finds start of keylen index in a node
 610  * @node: Pointer to the node structure to find the keylen index within
 611  *
 612  * Returns a pointer to the start of the key length index array
 613  * of the B+tree node *@node
 614  *
 615  * "The length of all the keys in the node is added to the size of the
 616  * header and then rounded up to a multiple of four to get the beginning
 617  * of the key length index" (p.88, practical filesystem design).
 618  *
 619  * Except that rounding up to 8 works, and rounding up to 4 doesn't.
 620  */
 621 static fs16 *
 622 befs_bt_keylen_index(struct befs_btree_node *node)
 623 {
 624         const int keylen_align = 8;
 625         unsigned long int off =
 626             (sizeof (befs_btree_nodehead) + node->head.all_key_length);
 627         ulong tmp = off % keylen_align;
 628 
 629         if (tmp)
 630                 off += keylen_align - tmp;
 631 
 632         return (fs16 *) ((void *) node->od_node + off);
 633 }
 634 
 635 /**
 636  * befs_bt_valarray - Finds the start of value array in a node
 637  * @node: Pointer to the node structure to find the value array within
 638  *
 639  * Returns a pointer to the start of the value array
 640  * of the node pointed to by the node header
 641  */
 642 static fs64 *
 643 befs_bt_valarray(struct befs_btree_node *node)
 644 {
 645         void *keylen_index_start = (void *) befs_bt_keylen_index(node);
 646         size_t keylen_index_size = node->head.all_key_count * sizeof (fs16);
 647 
 648         return (fs64 *) (keylen_index_start + keylen_index_size);
 649 }
 650 
 651 /**
 652  * befs_bt_keydata - Finds start of keydata array in a node
 653  * @node: Pointer to the node structure to find the keydata array within
 654  *
 655  * Returns a pointer to the start of the keydata array
 656  * of the node pointed to by the node header
 657  */
 658 static char *
 659 befs_bt_keydata(struct befs_btree_node *node)
 660 {
 661         return (char *) ((void *) node->od_node + sizeof (befs_btree_nodehead));
 662 }
 663 
 664 /**
 665  * befs_bt_get_key - returns a pointer to the start of a key
 666  * @sb: filesystem superblock
 667  * @node: node in which to look for the key
 668  * @index: the index of the key to get
 669  * @keylen: modified to be the length of the key at @index
 670  *
 671  * Returns a valid pointer into @node on success.
 672  * Returns NULL on failure (bad input) and sets *@keylen = 0
 673  */
 674 static char *
 675 befs_bt_get_key(struct super_block *sb, struct befs_btree_node *node,
 676                 int index, u16 * keylen)
 677 {
 678         int prev_key_end;
 679         char *keystart;
 680         fs16 *keylen_index;
 681 
 682         if (index < 0 || index > node->head.all_key_count) {
 683                 *keylen = 0;
 684                 return NULL;
 685         }
 686 
 687         keystart = befs_bt_keydata(node);
 688         keylen_index = befs_bt_keylen_index(node);
 689 
 690         if (index == 0)
 691                 prev_key_end = 0;
 692         else
 693                 prev_key_end = fs16_to_cpu(sb, keylen_index[index - 1]);
 694 
 695         *keylen = fs16_to_cpu(sb, keylen_index[index]) - prev_key_end;
 696 
 697         return keystart + prev_key_end;
 698 }
 699 
 700 /**
 701  * befs_compare_strings - compare two strings
 702  * @key1: pointer to the first key to be compared
 703  * @keylen1: length in bytes of key1
 704  * @key2: pointer to the second key to be compared
 705  * @keylen2: length in bytes of key2
 706  *
 707  * Returns 0 if @key1 and @key2 are equal.
 708  * Returns >0 if @key1 is greater.
 709  * Returns <0 if @key2 is greater.
 710  */
 711 static int
 712 befs_compare_strings(const void *key1, int keylen1,
 713                      const void *key2, int keylen2)
 714 {
 715         int len = min_t(int, keylen1, keylen2);
 716         int result = strncmp(key1, key2, len);
 717         if (result == 0)
 718                 result = keylen1 - keylen2;
 719         return result;
 720 }
 721 
 722 /* These will be used for non-string keyed btrees */
 723 #if 0
 724 static int
 725 btree_compare_int32(cont void *key1, int keylen1, const void *key2, int keylen2)
 726 {
 727         return *(int32_t *) key1 - *(int32_t *) key2;
 728 }
 729 
 730 static int
 731 btree_compare_uint32(cont void *key1, int keylen1,
 732                      const void *key2, int keylen2)
 733 {
 734         if (*(u_int32_t *) key1 == *(u_int32_t *) key2)
 735                 return 0;
 736         else if (*(u_int32_t *) key1 > *(u_int32_t *) key2)
 737                 return 1;
 738 
 739         return -1;
 740 }
 741 static int
 742 btree_compare_int64(cont void *key1, int keylen1, const void *key2, int keylen2)
 743 {
 744         if (*(int64_t *) key1 == *(int64_t *) key2)
 745                 return 0;
 746         else if (*(int64_t *) key1 > *(int64_t *) key2)
 747                 return 1;
 748 
 749         return -1;
 750 }
 751 
 752 static int
 753 btree_compare_uint64(cont void *key1, int keylen1,
 754                      const void *key2, int keylen2)
 755 {
 756         if (*(u_int64_t *) key1 == *(u_int64_t *) key2)
 757                 return 0;
 758         else if (*(u_int64_t *) key1 > *(u_int64_t *) key2)
 759                 return 1;
 760 
 761         return -1;
 762 }
 763 
 764 static int
 765 btree_compare_float(cont void *key1, int keylen1, const void *key2, int keylen2)
 766 {
 767         float result = *(float *) key1 - *(float *) key2;
 768         if (result == 0.0f)
 769                 return 0;
 770 
 771         return (result < 0.0f) ? -1 : 1;
 772 }
 773 
 774 static int
 775 btree_compare_double(cont void *key1, int keylen1,
 776                      const void *key2, int keylen2)
 777 {
 778         double result = *(double *) key1 - *(double *) key2;
 779         if (result == 0.0)
 780                 return 0;
 781 
 782         return (result < 0.0) ? -1 : 1;
 783 }
 784 #endif                          //0