btree.c 21.9 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787
/*
 * linux/fs/befs/btree.c
 *
 * Copyright (C) 2001-2002 Will Dyson <will_dyson@pobox.com>
 *
 * Licensed under the GNU GPL. See the file COPYING for details.
 *
 * 2002-02-05: Sergey S. Kostyliov added binary search withing
 * 		btree nodes.
 *
 * Many thanks to:
 *
 * Dominic Giampaolo, author of "Practical File System
 * Design with the Be File System", for such a helpful book.
 * 
 * Marcus J. Ranum, author of the b+tree package in 
 * comp.sources.misc volume 10. This code is not copied from that
 * work, but it is partially based on it.
 *
 * Makoto Kato, author of the original BeFS for linux filesystem
 * driver.
 */

#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/buffer_head.h>

#include "befs.h"
#include "btree.h"
#include "datastream.h"

/*
 * The btree functions in this file are built on top of the
 * datastream.c interface, which is in turn built on top of the
 * io.c interface.
 */

/* Befs B+tree structure:
 * 
 * The first thing in the tree is the tree superblock. It tells you
 * all kinds of useful things about the tree, like where the rootnode
 * is located, and the size of the nodes (always 1024 with current version
 * of BeOS).
 *
 * The rest of the tree consists of a series of nodes. Nodes contain a header
 * (struct befs_btree_nodehead), the packed key data, an array of shorts 
 * containing the ending offsets for each of the keys, and an array of
 * befs_off_t values. In interior nodes, the keys are the ending keys for 
 * the childnode they point to, and the values are offsets into the 
 * datastream containing the tree. 
 */

/* Note:
 * 
 * The book states 2 confusing things about befs b+trees. First, 
 * it states that the overflow field of node headers is used by internal nodes
 * to point to another node that "effectively continues this one". Here is what
 * I believe that means. Each key in internal nodes points to another node that
 * contains key values less than itself. Inspection reveals that the last key 
 * in the internal node is not the last key in the index. Keys that are 
 * greater than the last key in the internal node go into the overflow node. 
 * I imagine there is a performance reason for this.
 *
 * Second, it states that the header of a btree node is sufficient to 
 * distinguish internal nodes from leaf nodes. Without saying exactly how. 
 * After figuring out the first, it becomes obvious that internal nodes have
 * overflow nodes and leafnodes do not.
 */

/* 
 * Currently, this code is only good for directory B+trees.
 * In order to be used for other BFS indexes, it needs to be extended to handle
 * duplicate keys and non-string keytypes (int32, int64, float, double).
 */

/*
 * In memory structure of each btree node
 */
typedef struct {
	befs_host_btree_nodehead head;	/* head of node converted to cpu byteorder */
	struct buffer_head *bh;
	befs_btree_nodehead *od_node;	/* on disk node */
} befs_btree_node;

/* local constants */
static const befs_off_t befs_bt_inval = 0xffffffffffffffffULL;

/* local functions */
static int befs_btree_seekleaf(struct super_block *sb, befs_data_stream * ds,
			       befs_btree_super * bt_super,
			       befs_btree_node * this_node,
			       befs_off_t * node_off);

static int befs_bt_read_super(struct super_block *sb, befs_data_stream * ds,
			      befs_btree_super * sup);

static int befs_bt_read_node(struct super_block *sb, befs_data_stream * ds,
			     befs_btree_node * node, befs_off_t node_off);

static int befs_leafnode(befs_btree_node * node);

static fs16 *befs_bt_keylen_index(befs_btree_node * node);

static fs64 *befs_bt_valarray(befs_btree_node * node);

static char *befs_bt_keydata(befs_btree_node * node);

static int befs_find_key(struct super_block *sb, befs_btree_node * node,
			 const char *findkey, befs_off_t * value);

static char *befs_bt_get_key(struct super_block *sb, befs_btree_node * node,
			     int index, u16 * keylen);

static int befs_compare_strings(const void *key1, int keylen1,
				const void *key2, int keylen2);

/**
 * befs_bt_read_super - read in btree superblock convert to cpu byteorder
 * @sb: Filesystem superblock
 * @ds: Datastream to read from
 * @sup: Buffer in which to place the btree superblock
 *
 * Calls befs_read_datastream to read in the btree superblock and
 * makes sure it is in cpu byteorder, byteswapping if necessary.
 *
 * On success, returns BEFS_OK and *@sup contains the btree superblock,
 * in cpu byte order.
 *
 * On failure, BEFS_ERR is returned.
 */
static int
befs_bt_read_super(struct super_block *sb, befs_data_stream * ds,
		   befs_btree_super * sup)
{
	struct buffer_head *bh = NULL;
	befs_disk_btree_super *od_sup = NULL;

	befs_debug(sb, "---> befs_btree_read_super()");

	bh = befs_read_datastream(sb, ds, 0, NULL);

	if (!bh) {
		befs_error(sb, "Couldn't read index header.");
		goto error;
	}
	od_sup = (befs_disk_btree_super *) bh->b_data;
	befs_dump_index_entry(sb, od_sup);

	sup->magic = fs32_to_cpu(sb, od_sup->magic);
	sup->node_size = fs32_to_cpu(sb, od_sup->node_size);
	sup->max_depth = fs32_to_cpu(sb, od_sup->max_depth);
	sup->data_type = fs32_to_cpu(sb, od_sup->data_type);
	sup->root_node_ptr = fs64_to_cpu(sb, od_sup->root_node_ptr);
	sup->free_node_ptr = fs64_to_cpu(sb, od_sup->free_node_ptr);
	sup->max_size = fs64_to_cpu(sb, od_sup->max_size);

	brelse(bh);
	if (sup->magic != BEFS_BTREE_MAGIC) {
		befs_error(sb, "Index header has bad magic.");
		goto error;
	}

	befs_debug(sb, "<--- befs_btree_read_super()");
	return BEFS_OK;

      error:
	befs_debug(sb, "<--- befs_btree_read_super() ERROR");
	return BEFS_ERR;
}

/**
 * befs_bt_read_node - read in btree node and convert to cpu byteorder
 * @sb: Filesystem superblock
 * @ds: Datastream to read from
 * @node: Buffer in which to place the btree node
 * @node_off: Starting offset (in bytes) of the node in @ds
 *
 * Calls befs_read_datastream to read in the indicated btree node and
 * makes sure its header fields are in cpu byteorder, byteswapping if
 * necessary.
 * Note: node->bh must be NULL when this function called first
 * time. Don't forget brelse(node->bh) after last call.
 *
 * On success, returns BEFS_OK and *@node contains the btree node that
 * starts at @node_off, with the node->head fields in cpu byte order.
 *
 * On failure, BEFS_ERR is returned.
 */

static int
befs_bt_read_node(struct super_block *sb, befs_data_stream * ds,
		  befs_btree_node * node, befs_off_t node_off)
{
	uint off = 0;

	befs_debug(sb, "---> befs_bt_read_node()");

	if (node->bh)
		brelse(node->bh);

	node->bh = befs_read_datastream(sb, ds, node_off, &off);
	if (!node->bh) {
		befs_error(sb, "befs_bt_read_node() failed to read "
			   "node at %Lu", node_off);
		befs_debug(sb, "<--- befs_bt_read_node() ERROR");

		return BEFS_ERR;
	}
	node->od_node =
	    (befs_btree_nodehead *) ((void *) node->bh->b_data + off);

	befs_dump_index_node(sb, node->od_node);

	node->head.left = fs64_to_cpu(sb, node->od_node->left);
	node->head.right = fs64_to_cpu(sb, node->od_node->right);
	node->head.overflow = fs64_to_cpu(sb, node->od_node->overflow);
	node->head.all_key_count =
	    fs16_to_cpu(sb, node->od_node->all_key_count);
	node->head.all_key_length =
	    fs16_to_cpu(sb, node->od_node->all_key_length);

	befs_debug(sb, "<--- befs_btree_read_node()");
	return BEFS_OK;
}

/**
 * befs_btree_find - Find a key in a befs B+tree
 * @sb: Filesystem superblock
 * @ds: Datastream containing btree
 * @key: Key string to lookup in btree
 * @value: Value stored with @key
 *
 * On success, returns BEFS_OK and sets *@value to the value stored
 * with @key (usually the disk block number of an inode).
 *
 * On failure, returns BEFS_ERR or BEFS_BT_NOT_FOUND.
 * 
 * Algorithm: 
 *   Read the superblock and rootnode of the b+tree.
 *   Drill down through the interior nodes using befs_find_key().
 *   Once at the correct leaf node, use befs_find_key() again to get the
 *   actuall value stored with the key.
 */
int
befs_btree_find(struct super_block *sb, befs_data_stream * ds,
		const char *key, befs_off_t * value)
{
	befs_btree_node *this_node = NULL;
	befs_btree_super bt_super;
	befs_off_t node_off;
	int res;

	befs_debug(sb, "---> befs_btree_find() Key: %s", key);

	if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {
		befs_error(sb,
			   "befs_btree_find() failed to read index superblock");
		goto error;
	}

	this_node = kmalloc(sizeof (befs_btree_node),
						GFP_NOFS);
	if (!this_node) {
		befs_error(sb, "befs_btree_find() failed to allocate %u "
			   "bytes of memory", sizeof (befs_btree_node));
		goto error;
	}

	this_node->bh = NULL;

	/* read in root node */
	node_off = bt_super.root_node_ptr;
	if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
		befs_error(sb, "befs_btree_find() failed to read "
			   "node at %Lu", node_off);
		goto error_alloc;
	}

	while (!befs_leafnode(this_node)) {
		res = befs_find_key(sb, this_node, key, &node_off);
		if (res == BEFS_BT_NOT_FOUND)
			node_off = this_node->head.overflow;
		/* if no match, go to overflow node */
		if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
			befs_error(sb, "befs_btree_find() failed to read "
				   "node at %Lu", node_off);
			goto error_alloc;
		}
	}

	/* at the correct leaf node now */

	res = befs_find_key(sb, this_node, key, value);

	brelse(this_node->bh);
	kfree(this_node);

	if (res != BEFS_BT_MATCH) {
		befs_debug(sb, "<--- befs_btree_find() Key %s not found", key);
		*value = 0;
		return BEFS_BT_NOT_FOUND;
	}
	befs_debug(sb, "<--- befs_btree_find() Found key %s, value %Lu",
		   key, *value);
	return BEFS_OK;

      error_alloc:
	kfree(this_node);
      error:
	*value = 0;
	befs_debug(sb, "<--- befs_btree_find() ERROR");
	return BEFS_ERR;
}

/**
 * befs_find_key - Search for a key within a node
 * @sb: Filesystem superblock
 * @node: Node to find the key within
 * @key: Keystring to search for
 * @value: If key is found, the value stored with the key is put here
 *
 * finds exact match if one exists, and returns BEFS_BT_MATCH
 * If no exact match, finds first key in node that is greater
 * (alphabetically) than the search key and returns BEFS_BT_PARMATCH
 * (for partial match, I guess). Can you think of something better to
 * call it?
 *
 * If no key was a match or greater than the search key, return
 * BEFS_BT_NOT_FOUND.
 *
 * Use binary search instead of a linear.
 */
static int
befs_find_key(struct super_block *sb, befs_btree_node * node,
	      const char *findkey, befs_off_t * value)
{
	int first, last, mid;
	int eq;
	u16 keylen;
	int findkey_len;
	char *thiskey;
	fs64 *valarray;

	befs_debug(sb, "---> befs_find_key() %s", findkey);

	*value = 0;

	findkey_len = strlen(findkey);

	/* if node can not contain key, just skeep this node */
	last = node->head.all_key_count - 1;
	thiskey = befs_bt_get_key(sb, node, last, &keylen);

	eq = befs_compare_strings(thiskey, keylen, findkey, findkey_len);
	if (eq < 0) {
		befs_debug(sb, "<--- befs_find_key() %s not found", findkey);
		return BEFS_BT_NOT_FOUND;
	}

	valarray = befs_bt_valarray(node);

	/* simple binary search */
	first = 0;
	mid = 0;
	while (last >= first) {
		mid = (last + first) / 2;
		befs_debug(sb, "first: %d, last: %d, mid: %d", first, last,
			   mid);
		thiskey = befs_bt_get_key(sb, node, mid, &keylen);
		eq = befs_compare_strings(thiskey, keylen, findkey,
					  findkey_len);

		if (eq == 0) {
			befs_debug(sb, "<--- befs_find_key() found %s at %d",
				   thiskey, mid);

			*value = fs64_to_cpu(sb, valarray[mid]);
			return BEFS_BT_MATCH;
		}
		if (eq > 0)
			last = mid - 1;
		else
			first = mid + 1;
	}
	if (eq < 0)
		*value = fs64_to_cpu(sb, valarray[mid + 1]);
	else
		*value = fs64_to_cpu(sb, valarray[mid]);
	befs_debug(sb, "<--- befs_find_key() found %s at %d", thiskey, mid);
	return BEFS_BT_PARMATCH;
}

/**
 * befs_btree_read - Traverse leafnodes of a btree
 * @sb: Filesystem superblock
 * @ds: Datastream containing btree
 * @key_no: Key number (alphabetical order) of key to read
 * @bufsize: Size of the buffer to return key in
 * @keybuf: Pointer to a buffer to put the key in
 * @keysize: Length of the returned key
 * @value: Value stored with the returned key
 *
 * Heres how it works: Key_no is the index of the key/value pair to 
 * return in keybuf/value.
 * Bufsize is the size of keybuf (BEFS_NAME_LEN+1 is a good size). Keysize is 
 * the number of charecters in the key (just a convenience).
 *
 * Algorithm:
 *   Get the first leafnode of the tree. See if the requested key is in that
 *   node. If not, follow the node->right link to the next leafnode. Repeat 
 *   until the (key_no)th key is found or the tree is out of keys.
 */
int
befs_btree_read(struct super_block *sb, befs_data_stream * ds,
		loff_t key_no, size_t bufsize, char *keybuf, size_t * keysize,
		befs_off_t * value)
{
	befs_btree_node *this_node;
	befs_btree_super bt_super;
	befs_off_t node_off = 0;
	int cur_key;
	fs64 *valarray;
	char *keystart;
	u16 keylen;
	int res;

	uint key_sum = 0;

	befs_debug(sb, "---> befs_btree_read()");

	if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {
		befs_error(sb,
			   "befs_btree_read() failed to read index superblock");
		goto error;
	}

	if ((this_node = (befs_btree_node *)
	     kmalloc(sizeof (befs_btree_node), GFP_NOFS)) == NULL) {
		befs_error(sb, "befs_btree_read() failed to allocate %u "
			   "bytes of memory", sizeof (befs_btree_node));
		goto error;
	}

	node_off = bt_super.root_node_ptr;
	this_node->bh = NULL;

	/* seeks down to first leafnode, reads it into this_node */
	res = befs_btree_seekleaf(sb, ds, &bt_super, this_node, &node_off);
	if (res == BEFS_BT_EMPTY) {
		brelse(this_node->bh);
		kfree(this_node);
		*value = 0;
		*keysize = 0;
		befs_debug(sb, "<--- befs_btree_read() Tree is EMPTY");
		return BEFS_BT_EMPTY;
	} else if (res == BEFS_ERR) {
		goto error_alloc;
	}

	/* find the leaf node containing the key_no key */

	while (key_sum + this_node->head.all_key_count <= key_no) {

		/* no more nodes to look in: key_no is too large */
		if (this_node->head.right == befs_bt_inval) {
			*keysize = 0;
			*value = 0;
			befs_debug(sb,
				   "<--- befs_btree_read() END of keys at %Lu",
				   key_sum + this_node->head.all_key_count);
			brelse(this_node->bh);
			kfree(this_node);
			return BEFS_BT_END;
		}

		key_sum += this_node->head.all_key_count;
		node_off = this_node->head.right;

		if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
			befs_error(sb, "befs_btree_read() failed to read "
				   "node at %Lu", node_off);
			goto error_alloc;
		}
	}

	/* how many keys into this_node is key_no */
	cur_key = key_no - key_sum;

	/* get pointers to datastructures within the node body */
	valarray = befs_bt_valarray(this_node);

	keystart = befs_bt_get_key(sb, this_node, cur_key, &keylen);

	befs_debug(sb, "Read [%Lu,%d]: keysize %d", node_off, cur_key, keylen);

	if (bufsize < keylen + 1) {
		befs_error(sb, "befs_btree_read() keybuf too small (%u) "
			   "for key of size %d", bufsize, keylen);
		brelse(this_node->bh);
		goto error_alloc;
	};

	strncpy(keybuf, keystart, keylen);
	*value = fs64_to_cpu(sb, valarray[cur_key]);
	*keysize = keylen;
	keybuf[keylen] = '\0';

	befs_debug(sb, "Read [%Lu,%d]: Key \"%.*s\", Value %Lu", node_off,
		   cur_key, keylen, keybuf, *value);

	brelse(this_node->bh);
	kfree(this_node);

	befs_debug(sb, "<--- befs_btree_read()");

	return BEFS_OK;

      error_alloc:
	kfree(this_node);

      error:
	*keysize = 0;
	*value = 0;
	befs_debug(sb, "<--- befs_btree_read() ERROR");
	return BEFS_ERR;
}

/**
 * befs_btree_seekleaf - Find the first leafnode in the btree
 * @sb: Filesystem superblock
 * @ds: Datastream containing btree
 * @bt_super: Pointer to the superblock of the btree
 * @this_node: Buffer to return the leafnode in
 * @node_off: Pointer to offset of current node within datastream. Modified
 * 		by the function.
 *
 *
 * Helper function for btree traverse. Moves the current position to the 
 * start of the first leaf node.
 *
 * Also checks for an empty tree. If there are no keys, returns BEFS_BT_EMPTY.
 */
static int
befs_btree_seekleaf(struct super_block *sb, befs_data_stream * ds,
		    befs_btree_super * bt_super, befs_btree_node * this_node,
		    befs_off_t * node_off)
{

	befs_debug(sb, "---> befs_btree_seekleaf()");

	if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
		befs_error(sb, "befs_btree_seekleaf() failed to read "
			   "node at %Lu", *node_off);
		goto error;
	}
	befs_debug(sb, "Seekleaf to root node %Lu", *node_off);

	if (this_node->head.all_key_count == 0 && befs_leafnode(this_node)) {
		befs_debug(sb, "<--- befs_btree_seekleaf() Tree is EMPTY");
		return BEFS_BT_EMPTY;
	}

	while (!befs_leafnode(this_node)) {

		if (this_node->head.all_key_count == 0) {
			befs_debug(sb, "befs_btree_seekleaf() encountered "
				   "an empty interior node: %Lu. Using Overflow "
				   "node: %Lu", *node_off,
				   this_node->head.overflow);
			*node_off = this_node->head.overflow;
		} else {
			fs64 *valarray = befs_bt_valarray(this_node);
			*node_off = fs64_to_cpu(sb, valarray[0]);
		}
		if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
			befs_error(sb, "befs_btree_seekleaf() failed to read "
				   "node at %Lu", *node_off);
			goto error;
		}

		befs_debug(sb, "Seekleaf to child node %Lu", *node_off);
	}
	befs_debug(sb, "Node %Lu is a leaf node", *node_off);

	return BEFS_OK;

      error:
	befs_debug(sb, "<--- befs_btree_seekleaf() ERROR");
	return BEFS_ERR;
}

/**
 * befs_leafnode - Determine if the btree node is a leaf node or an 
 * interior node
 * @node: Pointer to node structure to test
 * 
 * Return 1 if leaf, 0 if interior
 */
static int
befs_leafnode(befs_btree_node * node)
{
	/* all interior nodes (and only interior nodes) have an overflow node */
	if (node->head.overflow == befs_bt_inval)
		return 1;
	else
		return 0;
}

/**
 * befs_bt_keylen_index - Finds start of keylen index in a node
 * @node: Pointer to the node structure to find the keylen index within
 *
 * Returns a pointer to the start of the key length index array
 * of the B+tree node *@node
 *
 * "The length of all the keys in the node is added to the size of the
 * header and then rounded up to a multiple of four to get the beginning
 * of the key length index" (p.88, practical filesystem design).
 *
 * Except that rounding up to 8 works, and rounding up to 4 doesn't.
 */
static fs16 *
befs_bt_keylen_index(befs_btree_node * node)
{
	const int keylen_align = 8;
	unsigned long int off =
	    (sizeof (befs_btree_nodehead) + node->head.all_key_length);
	ulong tmp = off % keylen_align;

	if (tmp)
		off += keylen_align - tmp;

	return (fs16 *) ((void *) node->od_node + off);
}

/**
 * befs_bt_valarray - Finds the start of value array in a node
 * @node: Pointer to the node structure to find the value array within
 *
 * Returns a pointer to the start of the value array
 * of the node pointed to by the node header
 */
static fs64 *
befs_bt_valarray(befs_btree_node * node)
{
	void *keylen_index_start = (void *) befs_bt_keylen_index(node);
	size_t keylen_index_size = node->head.all_key_count * sizeof (fs16);

	return (fs64 *) (keylen_index_start + keylen_index_size);
}

/**
 * befs_bt_keydata - Finds start of keydata array in a node
 * @node: Pointer to the node structure to find the keydata array within
 *
 * Returns a pointer to the start of the keydata array
 * of the node pointed to by the node header 
 */
static char *
befs_bt_keydata(befs_btree_node * node)
{
	return (char *) ((void *) node->od_node + sizeof (befs_btree_nodehead));
}

/**
 * befs_bt_get_key - returns a pointer to the start of a key
 * @sb: filesystem superblock
 * @node: node in which to look for the key
 * @index: the index of the key to get
 * @keylen: modified to be the length of the key at @index
 *
 * Returns a valid pointer into @node on success.
 * Returns NULL on failure (bad input) and sets *@keylen = 0
 */
static char *
befs_bt_get_key(struct super_block *sb, befs_btree_node * node,
		int index, u16 * keylen)
{
	int prev_key_end;
	char *keystart;
	fs16 *keylen_index;

	if (index < 0 || index > node->head.all_key_count) {
		*keylen = 0;
		return NULL;
	}

	keystart = befs_bt_keydata(node);
	keylen_index = befs_bt_keylen_index(node);

	if (index == 0)
		prev_key_end = 0;
	else
		prev_key_end = fs16_to_cpu(sb, keylen_index[index - 1]);

	*keylen = fs16_to_cpu(sb, keylen_index[index]) - prev_key_end;

	return keystart + prev_key_end;
}

/**
 * befs_compare_strings - compare two strings
 * @key1: pointer to the first key to be compared 
 * @keylen1: length in bytes of key1
 * @key2: pointer to the second key to be compared
 * @kelen2: length in bytes of key2
 *
 * Returns 0 if @key1 and @key2 are equal.
 * Returns >0 if @key1 is greater.
 * Returns <0 if @key2 is greater..
 */
static int
befs_compare_strings(const void *key1, int keylen1,
		     const void *key2, int keylen2)
{
	int len = min_t(int, keylen1, keylen2);
	int result = strncmp(key1, key2, len);
	if (result == 0)
		result = keylen1 - keylen2;
	return result;
}

/* These will be used for non-string keyed btrees */
#if 0
static int
btree_compare_int32(cont void *key1, int keylen1, const void *key2, int keylen2)
{
	return *(int32_t *) key1 - *(int32_t *) key2;
}

static int
btree_compare_uint32(cont void *key1, int keylen1,
		     const void *key2, int keylen2)
{
	if (*(u_int32_t *) key1 == *(u_int32_t *) key2)
		return 0;
	else if (*(u_int32_t *) key1 > *(u_int32_t *) key2)
		return 1;

	return -1;
}
static int
btree_compare_int64(cont void *key1, int keylen1, const void *key2, int keylen2)
{
	if (*(int64_t *) key1 == *(int64_t *) key2)
		return 0;
	else if (*(int64_t *) key1 > *(int64_t *) key2)
		return 1;

	return -1;
}

static int
btree_compare_uint64(cont void *key1, int keylen1,
		     const void *key2, int keylen2)
{
	if (*(u_int64_t *) key1 == *(u_int64_t *) key2)
		return 0;
	else if (*(u_int64_t *) key1 > *(u_int64_t *) key2)
		return 1;

	return -1;
}

static int
btree_compare_float(cont void *key1, int keylen1, const void *key2, int keylen2)
{
	float result = *(float *) key1 - *(float *) key2;
	if (result == 0.0f)
		return 0;

	return (result < 0.0f) ? -1 : 1;
}

static int
btree_compare_double(cont void *key1, int keylen1,
		     const void *key2, int keylen2)
{
	double result = *(double *) key1 - *(double *) key2;
	if (result == 0.0)
		return 0;

	return (result < 0.0) ? -1 : 1;
}
#endif				//0