xref: /openbmc/linux/fs/befs/btree.c (revision 32981ea5)
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  *
131  * On success, returns BEFS_OK and *@sup contains the btree superblock,
132  * in cpu byte order.
133  *
134  * On failure, BEFS_ERR is returned.
135  */
136 static int
137 befs_bt_read_super(struct super_block *sb, const befs_data_stream *ds,
138 		   befs_btree_super * sup)
139 {
140 	struct buffer_head *bh;
141 	befs_disk_btree_super *od_sup;
142 
143 	befs_debug(sb, "---> %s", __func__);
144 
145 	bh = befs_read_datastream(sb, ds, 0, NULL);
146 
147 	if (!bh) {
148 		befs_error(sb, "Couldn't read index header.");
149 		goto error;
150 	}
151 	od_sup = (befs_disk_btree_super *) bh->b_data;
152 	befs_dump_index_entry(sb, od_sup);
153 
154 	sup->magic = fs32_to_cpu(sb, od_sup->magic);
155 	sup->node_size = fs32_to_cpu(sb, od_sup->node_size);
156 	sup->max_depth = fs32_to_cpu(sb, od_sup->max_depth);
157 	sup->data_type = fs32_to_cpu(sb, od_sup->data_type);
158 	sup->root_node_ptr = fs64_to_cpu(sb, od_sup->root_node_ptr);
159 	sup->free_node_ptr = fs64_to_cpu(sb, od_sup->free_node_ptr);
160 	sup->max_size = fs64_to_cpu(sb, od_sup->max_size);
161 
162 	brelse(bh);
163 	if (sup->magic != BEFS_BTREE_MAGIC) {
164 		befs_error(sb, "Index header has bad magic.");
165 		goto error;
166 	}
167 
168 	befs_debug(sb, "<--- %s", __func__);
169 	return BEFS_OK;
170 
171       error:
172 	befs_debug(sb, "<--- %s ERROR", __func__);
173 	return BEFS_ERR;
174 }
175 
176 /**
177  * befs_bt_read_node - read in btree node and convert to cpu byteorder
178  * @sb: Filesystem superblock
179  * @ds: Datastream to read from
180  * @node: Buffer in which to place the btree node
181  * @node_off: Starting offset (in bytes) of the node in @ds
182  *
183  * Calls befs_read_datastream to read in the indicated btree node and
184  * makes sure its header fields are in cpu byteorder, byteswapping if
185  * necessary.
186  * Note: node->bh must be NULL when this function called first
187  * time. Don't forget brelse(node->bh) after last call.
188  *
189  * On success, returns BEFS_OK and *@node contains the btree node that
190  * starts at @node_off, with the node->head fields in cpu byte order.
191  *
192  * On failure, BEFS_ERR is returned.
193  */
194 
195 static int
196 befs_bt_read_node(struct super_block *sb, const befs_data_stream *ds,
197 		  struct befs_btree_node *node, befs_off_t node_off)
198 {
199 	uint off = 0;
200 
201 	befs_debug(sb, "---> %s", __func__);
202 
203 	if (node->bh)
204 		brelse(node->bh);
205 
206 	node->bh = befs_read_datastream(sb, ds, node_off, &off);
207 	if (!node->bh) {
208 		befs_error(sb, "%s failed to read "
209 			   "node at %llu", __func__, node_off);
210 		befs_debug(sb, "<--- %s ERROR", __func__);
211 
212 		return BEFS_ERR;
213 	}
214 	node->od_node =
215 	    (befs_btree_nodehead *) ((void *) node->bh->b_data + off);
216 
217 	befs_dump_index_node(sb, node->od_node);
218 
219 	node->head.left = fs64_to_cpu(sb, node->od_node->left);
220 	node->head.right = fs64_to_cpu(sb, node->od_node->right);
221 	node->head.overflow = fs64_to_cpu(sb, node->od_node->overflow);
222 	node->head.all_key_count =
223 	    fs16_to_cpu(sb, node->od_node->all_key_count);
224 	node->head.all_key_length =
225 	    fs16_to_cpu(sb, node->od_node->all_key_length);
226 
227 	befs_debug(sb, "<--- %s", __func__);
228 	return BEFS_OK;
229 }
230 
231 /**
232  * befs_btree_find - Find a key in a befs B+tree
233  * @sb: Filesystem superblock
234  * @ds: Datastream containing btree
235  * @key: Key string to lookup in btree
236  * @value: Value stored with @key
237  *
238  * On success, returns BEFS_OK and sets *@value to the value stored
239  * with @key (usually the disk block number of an inode).
240  *
241  * On failure, returns BEFS_ERR or BEFS_BT_NOT_FOUND.
242  *
243  * Algorithm:
244  *   Read the superblock and rootnode of the b+tree.
245  *   Drill down through the interior nodes using befs_find_key().
246  *   Once at the correct leaf node, use befs_find_key() again to get the
247  *   actuall value stored with the key.
248  */
249 int
250 befs_btree_find(struct super_block *sb, const befs_data_stream *ds,
251 		const char *key, befs_off_t * value)
252 {
253 	struct befs_btree_node *this_node;
254 	befs_btree_super bt_super;
255 	befs_off_t node_off;
256 	int res;
257 
258 	befs_debug(sb, "---> %s Key: %s", __func__, key);
259 
260 	if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {
261 		befs_error(sb,
262 			   "befs_btree_find() failed to read index superblock");
263 		goto error;
264 	}
265 
266 	this_node = kmalloc(sizeof(struct befs_btree_node),
267 						GFP_NOFS);
268 	if (!this_node) {
269 		befs_error(sb, "befs_btree_find() failed to allocate %zu "
270 			   "bytes of memory", sizeof(struct befs_btree_node));
271 		goto error;
272 	}
273 
274 	this_node->bh = NULL;
275 
276 	/* read in root node */
277 	node_off = bt_super.root_node_ptr;
278 	if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
279 		befs_error(sb, "befs_btree_find() failed to read "
280 			   "node at %llu", node_off);
281 		goto error_alloc;
282 	}
283 
284 	while (!befs_leafnode(this_node)) {
285 		res = befs_find_key(sb, this_node, key, &node_off);
286 		if (res == BEFS_BT_NOT_FOUND)
287 			node_off = this_node->head.overflow;
288 		/* if no match, go to overflow node */
289 		if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
290 			befs_error(sb, "befs_btree_find() failed to read "
291 				   "node at %llu", node_off);
292 			goto error_alloc;
293 		}
294 	}
295 
296 	/* at the correct leaf node now */
297 
298 	res = befs_find_key(sb, this_node, key, value);
299 
300 	brelse(this_node->bh);
301 	kfree(this_node);
302 
303 	if (res != BEFS_BT_MATCH) {
304 		befs_debug(sb, "<--- %s Key %s not found", __func__, key);
305 		*value = 0;
306 		return BEFS_BT_NOT_FOUND;
307 	}
308 	befs_debug(sb, "<--- %s Found key %s, value %llu", __func__,
309 		   key, *value);
310 	return BEFS_OK;
311 
312       error_alloc:
313 	kfree(this_node);
314       error:
315 	*value = 0;
316 	befs_debug(sb, "<--- %s ERROR", __func__);
317 	return BEFS_ERR;
318 }
319 
320 /**
321  * befs_find_key - Search for a key within a node
322  * @sb: Filesystem superblock
323  * @node: Node to find the key within
324  * @findkey: Keystring to search for
325  * @value: If key is found, the value stored with the key is put here
326  *
327  * finds exact match if one exists, and returns BEFS_BT_MATCH
328  * If no exact match, finds first key in node that is greater
329  * (alphabetically) than the search key and returns BEFS_BT_PARMATCH
330  * (for partial match, I guess). Can you think of something better to
331  * call it?
332  *
333  * If no key was a match or greater than the search key, return
334  * BEFS_BT_NOT_FOUND.
335  *
336  * Use binary search instead of a linear.
337  */
338 static int
339 befs_find_key(struct super_block *sb, struct befs_btree_node *node,
340 	      const char *findkey, befs_off_t * value)
341 {
342 	int first, last, mid;
343 	int eq;
344 	u16 keylen;
345 	int findkey_len;
346 	char *thiskey;
347 	fs64 *valarray;
348 
349 	befs_debug(sb, "---> %s %s", __func__, findkey);
350 
351 	*value = 0;
352 
353 	findkey_len = strlen(findkey);
354 
355 	/* if node can not contain key, just skeep this node */
356 	last = node->head.all_key_count - 1;
357 	thiskey = befs_bt_get_key(sb, node, last, &keylen);
358 
359 	eq = befs_compare_strings(thiskey, keylen, findkey, findkey_len);
360 	if (eq < 0) {
361 		befs_debug(sb, "<--- %s %s not found", __func__, findkey);
362 		return BEFS_BT_NOT_FOUND;
363 	}
364 
365 	valarray = befs_bt_valarray(node);
366 
367 	/* simple binary search */
368 	first = 0;
369 	mid = 0;
370 	while (last >= first) {
371 		mid = (last + first) / 2;
372 		befs_debug(sb, "first: %d, last: %d, mid: %d", first, last,
373 			   mid);
374 		thiskey = befs_bt_get_key(sb, node, mid, &keylen);
375 		eq = befs_compare_strings(thiskey, keylen, findkey,
376 					  findkey_len);
377 
378 		if (eq == 0) {
379 			befs_debug(sb, "<--- %s found %s at %d",
380 				   __func__, thiskey, mid);
381 
382 			*value = fs64_to_cpu(sb, valarray[mid]);
383 			return BEFS_BT_MATCH;
384 		}
385 		if (eq > 0)
386 			last = mid - 1;
387 		else
388 			first = mid + 1;
389 	}
390 	if (eq < 0)
391 		*value = fs64_to_cpu(sb, valarray[mid + 1]);
392 	else
393 		*value = fs64_to_cpu(sb, valarray[mid]);
394 	befs_debug(sb, "<--- %s found %s at %d", __func__, thiskey, mid);
395 	return BEFS_BT_PARMATCH;
396 }
397 
398 /**
399  * befs_btree_read - Traverse leafnodes of a btree
400  * @sb: Filesystem superblock
401  * @ds: Datastream containing btree
402  * @key_no: Key number (alphabetical order) of key to read
403  * @bufsize: Size of the buffer to return key in
404  * @keybuf: Pointer to a buffer to put the key in
405  * @keysize: Length of the returned key
406  * @value: Value stored with the returned key
407  *
408  * Heres how it works: Key_no is the index of the key/value pair to
409  * return in keybuf/value.
410  * Bufsize is the size of keybuf (BEFS_NAME_LEN+1 is a good size). Keysize is
411  * the number of characters in the key (just a convenience).
412  *
413  * Algorithm:
414  *   Get the first leafnode of the tree. See if the requested key is in that
415  *   node. If not, follow the node->right link to the next leafnode. Repeat
416  *   until the (key_no)th key is found or the tree is out of keys.
417  */
418 int
419 befs_btree_read(struct super_block *sb, const befs_data_stream *ds,
420 		loff_t key_no, size_t bufsize, char *keybuf, size_t * keysize,
421 		befs_off_t * value)
422 {
423 	struct befs_btree_node *this_node;
424 	befs_btree_super bt_super;
425 	befs_off_t node_off = 0;
426 	int cur_key;
427 	fs64 *valarray;
428 	char *keystart;
429 	u16 keylen;
430 	int res;
431 
432 	uint key_sum = 0;
433 
434 	befs_debug(sb, "---> %s", __func__);
435 
436 	if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {
437 		befs_error(sb,
438 			   "befs_btree_read() failed to read index superblock");
439 		goto error;
440 	}
441 
442 	this_node = kmalloc(sizeof(struct befs_btree_node), GFP_NOFS);
443 	if (this_node == NULL) {
444 		befs_error(sb, "befs_btree_read() failed to allocate %zu "
445 			   "bytes of memory", sizeof(struct befs_btree_node));
446 		goto error;
447 	}
448 
449 	node_off = bt_super.root_node_ptr;
450 	this_node->bh = NULL;
451 
452 	/* seeks down to first leafnode, reads it into this_node */
453 	res = befs_btree_seekleaf(sb, ds, &bt_super, this_node, &node_off);
454 	if (res == BEFS_BT_EMPTY) {
455 		brelse(this_node->bh);
456 		kfree(this_node);
457 		*value = 0;
458 		*keysize = 0;
459 		befs_debug(sb, "<--- %s Tree is EMPTY", __func__);
460 		return BEFS_BT_EMPTY;
461 	} else if (res == BEFS_ERR) {
462 		goto error_alloc;
463 	}
464 
465 	/* find the leaf node containing the key_no key */
466 
467 	while (key_sum + this_node->head.all_key_count <= key_no) {
468 
469 		/* no more nodes to look in: key_no is too large */
470 		if (this_node->head.right == befs_bt_inval) {
471 			*keysize = 0;
472 			*value = 0;
473 			befs_debug(sb,
474 				   "<--- %s END of keys at %llu", __func__,
475 				   (unsigned long long)
476 				   key_sum + this_node->head.all_key_count);
477 			brelse(this_node->bh);
478 			kfree(this_node);
479 			return BEFS_BT_END;
480 		}
481 
482 		key_sum += this_node->head.all_key_count;
483 		node_off = this_node->head.right;
484 
485 		if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
486 			befs_error(sb, "%s failed to read node at %llu",
487 				  __func__, (unsigned long long)node_off);
488 			goto error_alloc;
489 		}
490 	}
491 
492 	/* how many keys into this_node is key_no */
493 	cur_key = key_no - key_sum;
494 
495 	/* get pointers to datastructures within the node body */
496 	valarray = befs_bt_valarray(this_node);
497 
498 	keystart = befs_bt_get_key(sb, this_node, cur_key, &keylen);
499 
500 	befs_debug(sb, "Read [%llu,%d]: keysize %d",
501 		   (long long unsigned int)node_off, (int)cur_key,
502 		   (int)keylen);
503 
504 	if (bufsize < keylen + 1) {
505 		befs_error(sb, "%s keybuf too small (%zu) "
506 			   "for key of size %d", __func__, bufsize, keylen);
507 		brelse(this_node->bh);
508 		goto error_alloc;
509 	}
510 
511 	strlcpy(keybuf, keystart, keylen + 1);
512 	*value = fs64_to_cpu(sb, valarray[cur_key]);
513 	*keysize = keylen;
514 
515 	befs_debug(sb, "Read [%llu,%d]: Key \"%.*s\", Value %llu", node_off,
516 		   cur_key, keylen, keybuf, *value);
517 
518 	brelse(this_node->bh);
519 	kfree(this_node);
520 
521 	befs_debug(sb, "<--- %s", __func__);
522 
523 	return BEFS_OK;
524 
525       error_alloc:
526 	kfree(this_node);
527 
528       error:
529 	*keysize = 0;
530 	*value = 0;
531 	befs_debug(sb, "<--- %s ERROR", __func__);
532 	return BEFS_ERR;
533 }
534 
535 /**
536  * befs_btree_seekleaf - Find the first leafnode in the btree
537  * @sb: Filesystem superblock
538  * @ds: Datastream containing btree
539  * @bt_super: Pointer to the superblock of the btree
540  * @this_node: Buffer to return the leafnode in
541  * @node_off: Pointer to offset of current node within datastream. Modified
542  * 		by the function.
543  *
544  *
545  * Helper function for btree traverse. Moves the current position to the
546  * start of the first leaf node.
547  *
548  * Also checks for an empty tree. If there are no keys, returns BEFS_BT_EMPTY.
549  */
550 static int
551 befs_btree_seekleaf(struct super_block *sb, const befs_data_stream *ds,
552 		    befs_btree_super *bt_super,
553 		    struct befs_btree_node *this_node,
554 		    befs_off_t * node_off)
555 {
556 
557 	befs_debug(sb, "---> %s", __func__);
558 
559 	if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
560 		befs_error(sb, "%s failed to read "
561 			   "node at %llu", __func__, *node_off);
562 		goto error;
563 	}
564 	befs_debug(sb, "Seekleaf to root node %llu", *node_off);
565 
566 	if (this_node->head.all_key_count == 0 && befs_leafnode(this_node)) {
567 		befs_debug(sb, "<--- %s Tree is EMPTY", __func__);
568 		return BEFS_BT_EMPTY;
569 	}
570 
571 	while (!befs_leafnode(this_node)) {
572 
573 		if (this_node->head.all_key_count == 0) {
574 			befs_debug(sb, "%s encountered "
575 				   "an empty interior node: %llu. Using Overflow "
576 				   "node: %llu", __func__, *node_off,
577 				   this_node->head.overflow);
578 			*node_off = this_node->head.overflow;
579 		} else {
580 			fs64 *valarray = befs_bt_valarray(this_node);
581 			*node_off = fs64_to_cpu(sb, valarray[0]);
582 		}
583 		if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
584 			befs_error(sb, "%s failed to read "
585 				   "node at %llu", __func__, *node_off);
586 			goto error;
587 		}
588 
589 		befs_debug(sb, "Seekleaf to child node %llu", *node_off);
590 	}
591 	befs_debug(sb, "Node %llu is a leaf node", *node_off);
592 
593 	return BEFS_OK;
594 
595       error:
596 	befs_debug(sb, "<--- %s ERROR", __func__);
597 	return BEFS_ERR;
598 }
599 
600 /**
601  * befs_leafnode - Determine if the btree node is a leaf node or an
602  * interior node
603  * @node: Pointer to node structure to test
604  *
605  * Return 1 if leaf, 0 if interior
606  */
607 static int
608 befs_leafnode(struct befs_btree_node *node)
609 {
610 	/* all interior nodes (and only interior nodes) have an overflow node */
611 	if (node->head.overflow == befs_bt_inval)
612 		return 1;
613 	else
614 		return 0;
615 }
616 
617 /**
618  * befs_bt_keylen_index - Finds start of keylen index in a node
619  * @node: Pointer to the node structure to find the keylen index within
620  *
621  * Returns a pointer to the start of the key length index array
622  * of the B+tree node *@node
623  *
624  * "The length of all the keys in the node is added to the size of the
625  * header and then rounded up to a multiple of four to get the beginning
626  * of the key length index" (p.88, practical filesystem design).
627  *
628  * Except that rounding up to 8 works, and rounding up to 4 doesn't.
629  */
630 static fs16 *
631 befs_bt_keylen_index(struct befs_btree_node *node)
632 {
633 	const int keylen_align = 8;
634 	unsigned long int off =
635 	    (sizeof (befs_btree_nodehead) + node->head.all_key_length);
636 	ulong tmp = off % keylen_align;
637 
638 	if (tmp)
639 		off += keylen_align - tmp;
640 
641 	return (fs16 *) ((void *) node->od_node + off);
642 }
643 
644 /**
645  * befs_bt_valarray - Finds the start of value array in a node
646  * @node: Pointer to the node structure to find the value array within
647  *
648  * Returns a pointer to the start of the value array
649  * of the node pointed to by the node header
650  */
651 static fs64 *
652 befs_bt_valarray(struct befs_btree_node *node)
653 {
654 	void *keylen_index_start = (void *) befs_bt_keylen_index(node);
655 	size_t keylen_index_size = node->head.all_key_count * sizeof (fs16);
656 
657 	return (fs64 *) (keylen_index_start + keylen_index_size);
658 }
659 
660 /**
661  * befs_bt_keydata - Finds start of keydata array in a node
662  * @node: Pointer to the node structure to find the keydata array within
663  *
664  * Returns a pointer to the start of the keydata array
665  * of the node pointed to by the node header
666  */
667 static char *
668 befs_bt_keydata(struct befs_btree_node *node)
669 {
670 	return (char *) ((void *) node->od_node + sizeof (befs_btree_nodehead));
671 }
672 
673 /**
674  * befs_bt_get_key - returns a pointer to the start of a key
675  * @sb: filesystem superblock
676  * @node: node in which to look for the key
677  * @index: the index of the key to get
678  * @keylen: modified to be the length of the key at @index
679  *
680  * Returns a valid pointer into @node on success.
681  * Returns NULL on failure (bad input) and sets *@keylen = 0
682  */
683 static char *
684 befs_bt_get_key(struct super_block *sb, struct befs_btree_node *node,
685 		int index, u16 * keylen)
686 {
687 	int prev_key_end;
688 	char *keystart;
689 	fs16 *keylen_index;
690 
691 	if (index < 0 || index > node->head.all_key_count) {
692 		*keylen = 0;
693 		return NULL;
694 	}
695 
696 	keystart = befs_bt_keydata(node);
697 	keylen_index = befs_bt_keylen_index(node);
698 
699 	if (index == 0)
700 		prev_key_end = 0;
701 	else
702 		prev_key_end = fs16_to_cpu(sb, keylen_index[index - 1]);
703 
704 	*keylen = fs16_to_cpu(sb, keylen_index[index]) - prev_key_end;
705 
706 	return keystart + prev_key_end;
707 }
708 
709 /**
710  * befs_compare_strings - compare two strings
711  * @key1: pointer to the first key to be compared
712  * @keylen1: length in bytes of key1
713  * @key2: pointer to the second key to be compared
714  * @keylen2: length in bytes of key2
715  *
716  * Returns 0 if @key1 and @key2 are equal.
717  * Returns >0 if @key1 is greater.
718  * Returns <0 if @key2 is greater..
719  */
720 static int
721 befs_compare_strings(const void *key1, int keylen1,
722 		     const void *key2, int keylen2)
723 {
724 	int len = min_t(int, keylen1, keylen2);
725 	int result = strncmp(key1, key2, len);
726 	if (result == 0)
727 		result = keylen1 - keylen2;
728 	return result;
729 }
730 
731 /* These will be used for non-string keyed btrees */
732 #if 0
733 static int
734 btree_compare_int32(cont void *key1, int keylen1, const void *key2, int keylen2)
735 {
736 	return *(int32_t *) key1 - *(int32_t *) key2;
737 }
738 
739 static int
740 btree_compare_uint32(cont void *key1, int keylen1,
741 		     const void *key2, int keylen2)
742 {
743 	if (*(u_int32_t *) key1 == *(u_int32_t *) key2)
744 		return 0;
745 	else if (*(u_int32_t *) key1 > *(u_int32_t *) key2)
746 		return 1;
747 
748 	return -1;
749 }
750 static int
751 btree_compare_int64(cont void *key1, int keylen1, const void *key2, int keylen2)
752 {
753 	if (*(int64_t *) key1 == *(int64_t *) key2)
754 		return 0;
755 	else if (*(int64_t *) key1 > *(int64_t *) key2)
756 		return 1;
757 
758 	return -1;
759 }
760 
761 static int
762 btree_compare_uint64(cont void *key1, int keylen1,
763 		     const void *key2, int keylen2)
764 {
765 	if (*(u_int64_t *) key1 == *(u_int64_t *) key2)
766 		return 0;
767 	else if (*(u_int64_t *) key1 > *(u_int64_t *) key2)
768 		return 1;
769 
770 	return -1;
771 }
772 
773 static int
774 btree_compare_float(cont void *key1, int keylen1, const void *key2, int keylen2)
775 {
776 	float result = *(float *) key1 - *(float *) key2;
777 	if (result == 0.0f)
778 		return 0;
779 
780 	return (result < 0.0f) ? -1 : 1;
781 }
782 
783 static int
784 btree_compare_double(cont void *key1, int keylen1,
785 		     const void *key2, int keylen2)
786 {
787 	double result = *(double *) key1 - *(double *) key2;
788 	if (result == 0.0)
789 		return 0;
790 
791 	return (result < 0.0) ? -1 : 1;
792 }
793 #endif				//0
794