aboutsummaryrefslogtreecommitdiff
path: root/fs/befs/btree.c
blob: a66c9b1136e06d8d4ab4ef40cad62c69aee4cae1 (plain)
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 within
 * 		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