xref: /openbmc/linux/fs/befs/btree.c (revision 6dfcd296)
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 
160 	brelse(bh);
161 	if (sup->magic != BEFS_BTREE_MAGIC) {
162 		befs_error(sb, "Index header has bad magic.");
163 		goto error;
164 	}
165 
166 	befs_debug(sb, "<--- %s", __func__);
167 	return BEFS_OK;
168 
169       error:
170 	befs_debug(sb, "<--- %s ERROR", __func__);
171 	return BEFS_ERR;
172 }
173 
174 /**
175  * befs_bt_read_node - read in btree node and convert to cpu byteorder
176  * @sb: Filesystem superblock
177  * @ds: Datastream to read from
178  * @node: Buffer in which to place the btree node
179  * @node_off: Starting offset (in bytes) of the node in @ds
180  *
181  * Calls befs_read_datastream to read in the indicated btree node and
182  * makes sure its header fields are in cpu byteorder, byteswapping if
183  * necessary.
184  * Note: node->bh must be NULL when this function is called the first time.
185  * Don't forget brelse(node->bh) after last call.
186  *
187  * On success, returns BEFS_OK and *@node contains the btree node that
188  * starts at @node_off, with the node->head fields in cpu byte order.
189  *
190  * On failure, BEFS_ERR is returned.
191  */
192 
193 static int
194 befs_bt_read_node(struct super_block *sb, const befs_data_stream *ds,
195 		  struct befs_btree_node *node, befs_off_t node_off)
196 {
197 	uint off = 0;
198 
199 	befs_debug(sb, "---> %s", __func__);
200 
201 	if (node->bh)
202 		brelse(node->bh);
203 
204 	node->bh = befs_read_datastream(sb, ds, node_off, &off);
205 	if (!node->bh) {
206 		befs_error(sb, "%s failed to read "
207 			   "node at %llu", __func__, node_off);
208 		befs_debug(sb, "<--- %s ERROR", __func__);
209 
210 		return BEFS_ERR;
211 	}
212 	node->od_node =
213 	    (befs_btree_nodehead *) ((void *) node->bh->b_data + off);
214 
215 	befs_dump_index_node(sb, node->od_node);
216 
217 	node->head.left = fs64_to_cpu(sb, node->od_node->left);
218 	node->head.right = fs64_to_cpu(sb, node->od_node->right);
219 	node->head.overflow = fs64_to_cpu(sb, node->od_node->overflow);
220 	node->head.all_key_count =
221 	    fs16_to_cpu(sb, node->od_node->all_key_count);
222 	node->head.all_key_length =
223 	    fs16_to_cpu(sb, node->od_node->all_key_length);
224 
225 	befs_debug(sb, "<--- %s", __func__);
226 	return BEFS_OK;
227 }
228 
229 /**
230  * befs_btree_find - Find a key in a befs B+tree
231  * @sb: Filesystem superblock
232  * @ds: Datastream containing btree
233  * @key: Key string to lookup in btree
234  * @value: Value stored with @key
235  *
236  * On success, returns BEFS_OK and sets *@value to the value stored
237  * with @key (usually the disk block number of an inode).
238  *
239  * On failure, returns BEFS_ERR or BEFS_BT_NOT_FOUND.
240  *
241  * Algorithm:
242  *   Read the superblock and rootnode of the b+tree.
243  *   Drill down through the interior nodes using befs_find_key().
244  *   Once at the correct leaf node, use befs_find_key() again to get the
245  *   actual value stored with the key.
246  */
247 int
248 befs_btree_find(struct super_block *sb, const befs_data_stream *ds,
249 		const char *key, befs_off_t * value)
250 {
251 	struct befs_btree_node *this_node;
252 	befs_btree_super bt_super;
253 	befs_off_t node_off;
254 	int res;
255 
256 	befs_debug(sb, "---> %s Key: %s", __func__, key);
257 
258 	if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {
259 		befs_error(sb,
260 			   "befs_btree_find() failed to read index superblock");
261 		goto error;
262 	}
263 
264 	this_node = kmalloc(sizeof(struct befs_btree_node),
265 						GFP_NOFS);
266 	if (!this_node) {
267 		befs_error(sb, "befs_btree_find() failed to allocate %zu "
268 			   "bytes of memory", sizeof(struct befs_btree_node));
269 		goto error;
270 	}
271 
272 	this_node->bh = NULL;
273 
274 	/* read in root node */
275 	node_off = bt_super.root_node_ptr;
276 	if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
277 		befs_error(sb, "befs_btree_find() failed to read "
278 			   "node at %llu", node_off);
279 		goto error_alloc;
280 	}
281 
282 	while (!befs_leafnode(this_node)) {
283 		res = befs_find_key(sb, this_node, key, &node_off);
284 		/* if no key set, try the overflow node */
285 		if (res == BEFS_BT_OVERFLOW)
286 			node_off = this_node->head.overflow;
287 		if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
288 			befs_error(sb, "befs_btree_find() failed to read "
289 				   "node at %llu", node_off);
290 			goto error_alloc;
291 		}
292 	}
293 
294 	/* at a leaf node now, check if it is correct */
295 	res = befs_find_key(sb, this_node, key, value);
296 
297 	brelse(this_node->bh);
298 	kfree(this_node);
299 
300 	if (res != BEFS_BT_MATCH) {
301 		befs_error(sb, "<--- %s Key %s not found", __func__, key);
302 		befs_debug(sb, "<--- %s ERROR", __func__);
303 		*value = 0;
304 		return BEFS_BT_NOT_FOUND;
305 	}
306 	befs_debug(sb, "<--- %s Found key %s, value %llu", __func__,
307 		   key, *value);
308 	return BEFS_OK;
309 
310       error_alloc:
311 	kfree(this_node);
312       error:
313 	*value = 0;
314 	befs_debug(sb, "<--- %s ERROR", __func__);
315 	return BEFS_ERR;
316 }
317 
318 /**
319  * befs_find_key - Search for a key within a node
320  * @sb: Filesystem superblock
321  * @node: Node to find the key within
322  * @findkey: Keystring to search for
323  * @value: If key is found, the value stored with the key is put here
324  *
325  * Finds exact match if one exists, and returns BEFS_BT_MATCH.
326  * If there is no match and node's value array is too small for key, return
327  * BEFS_BT_OVERFLOW.
328  * If no match and node should countain this key, return BEFS_BT_NOT_FOUND.
329  *
330  * Uses binary search instead of a linear.
331  */
332 static int
333 befs_find_key(struct super_block *sb, struct befs_btree_node *node,
334 	      const char *findkey, befs_off_t * value)
335 {
336 	int first, last, mid;
337 	int eq;
338 	u16 keylen;
339 	int findkey_len;
340 	char *thiskey;
341 	fs64 *valarray;
342 
343 	befs_debug(sb, "---> %s %s", __func__, findkey);
344 
345 	findkey_len = strlen(findkey);
346 
347 	/* if node can not contain key, just skip this node */
348 	last = node->head.all_key_count - 1;
349 	thiskey = befs_bt_get_key(sb, node, last, &keylen);
350 
351 	eq = befs_compare_strings(thiskey, keylen, findkey, findkey_len);
352 	if (eq < 0) {
353 		befs_debug(sb, "<--- node can't contain %s", findkey);
354 		return BEFS_BT_OVERFLOW;
355 	}
356 
357 	valarray = befs_bt_valarray(node);
358 
359 	/* simple binary search */
360 	first = 0;
361 	mid = 0;
362 	while (last >= first) {
363 		mid = (last + first) / 2;
364 		befs_debug(sb, "first: %d, last: %d, mid: %d", first, last,
365 			   mid);
366 		thiskey = befs_bt_get_key(sb, node, mid, &keylen);
367 		eq = befs_compare_strings(thiskey, keylen, findkey,
368 					  findkey_len);
369 
370 		if (eq == 0) {
371 			befs_debug(sb, "<--- %s found %s at %d",
372 				   __func__, thiskey, mid);
373 
374 			*value = fs64_to_cpu(sb, valarray[mid]);
375 			return BEFS_BT_MATCH;
376 		}
377 		if (eq > 0)
378 			last = mid - 1;
379 		else
380 			first = mid + 1;
381 	}
382 
383 	/* return an existing value so caller can arrive to a leaf node */
384 	if (eq < 0)
385 		*value = fs64_to_cpu(sb, valarray[mid + 1]);
386 	else
387 		*value = fs64_to_cpu(sb, valarray[mid]);
388 	befs_error(sb, "<--- %s %s not found", __func__, findkey);
389 	befs_debug(sb, "<--- %s ERROR", __func__);
390 	return BEFS_BT_NOT_FOUND;
391 }
392 
393 /**
394  * befs_btree_read - Traverse leafnodes of a btree
395  * @sb: Filesystem superblock
396  * @ds: Datastream containing btree
397  * @key_no: Key number (alphabetical order) of key to read
398  * @bufsize: Size of the buffer to return key in
399  * @keybuf: Pointer to a buffer to put the key in
400  * @keysize: Length of the returned key
401  * @value: Value stored with the returned key
402  *
403  * Here's how it works: Key_no is the index of the key/value pair to
404  * return in keybuf/value.
405  * Bufsize is the size of keybuf (BEFS_NAME_LEN+1 is a good size). Keysize is
406  * the number of characters in the key (just a convenience).
407  *
408  * Algorithm:
409  *   Get the first leafnode of the tree. See if the requested key is in that
410  *   node. If not, follow the node->right link to the next leafnode. Repeat
411  *   until the (key_no)th key is found or the tree is out of keys.
412  */
413 int
414 befs_btree_read(struct super_block *sb, const befs_data_stream *ds,
415 		loff_t key_no, size_t bufsize, char *keybuf, size_t * keysize,
416 		befs_off_t * value)
417 {
418 	struct befs_btree_node *this_node;
419 	befs_btree_super bt_super;
420 	befs_off_t node_off;
421 	int cur_key;
422 	fs64 *valarray;
423 	char *keystart;
424 	u16 keylen;
425 	int res;
426 
427 	uint key_sum = 0;
428 
429 	befs_debug(sb, "---> %s", __func__);
430 
431 	if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {
432 		befs_error(sb,
433 			   "befs_btree_read() failed to read index superblock");
434 		goto error;
435 	}
436 
437 	this_node = kmalloc(sizeof(struct befs_btree_node), GFP_NOFS);
438 	if (this_node == NULL) {
439 		befs_error(sb, "befs_btree_read() failed to allocate %zu "
440 			   "bytes of memory", sizeof(struct befs_btree_node));
441 		goto error;
442 	}
443 
444 	node_off = bt_super.root_node_ptr;
445 	this_node->bh = NULL;
446 
447 	/* seeks down to first leafnode, reads it into this_node */
448 	res = befs_btree_seekleaf(sb, ds, &bt_super, this_node, &node_off);
449 	if (res == BEFS_BT_EMPTY) {
450 		brelse(this_node->bh);
451 		kfree(this_node);
452 		*value = 0;
453 		*keysize = 0;
454 		befs_debug(sb, "<--- %s Tree is EMPTY", __func__);
455 		return BEFS_BT_EMPTY;
456 	} else if (res == BEFS_ERR) {
457 		goto error_alloc;
458 	}
459 
460 	/* find the leaf node containing the key_no key */
461 
462 	while (key_sum + this_node->head.all_key_count <= key_no) {
463 
464 		/* no more nodes to look in: key_no is too large */
465 		if (this_node->head.right == BEFS_BT_INVAL) {
466 			*keysize = 0;
467 			*value = 0;
468 			befs_debug(sb,
469 				   "<--- %s END of keys at %llu", __func__,
470 				   (unsigned long long)
471 				   key_sum + this_node->head.all_key_count);
472 			brelse(this_node->bh);
473 			kfree(this_node);
474 			return BEFS_BT_END;
475 		}
476 
477 		key_sum += this_node->head.all_key_count;
478 		node_off = this_node->head.right;
479 
480 		if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
481 			befs_error(sb, "%s failed to read node at %llu",
482 				  __func__, (unsigned long long)node_off);
483 			goto error_alloc;
484 		}
485 	}
486 
487 	/* how many keys into this_node is key_no */
488 	cur_key = key_no - key_sum;
489 
490 	/* get pointers to datastructures within the node body */
491 	valarray = befs_bt_valarray(this_node);
492 
493 	keystart = befs_bt_get_key(sb, this_node, cur_key, &keylen);
494 
495 	befs_debug(sb, "Read [%llu,%d]: keysize %d",
496 		   (long long unsigned int)node_off, (int)cur_key,
497 		   (int)keylen);
498 
499 	if (bufsize < keylen + 1) {
500 		befs_error(sb, "%s keybuf too small (%zu) "
501 			   "for key of size %d", __func__, bufsize, keylen);
502 		brelse(this_node->bh);
503 		goto error_alloc;
504 	}
505 
506 	strlcpy(keybuf, keystart, keylen + 1);
507 	*value = fs64_to_cpu(sb, valarray[cur_key]);
508 	*keysize = keylen;
509 
510 	befs_debug(sb, "Read [%llu,%d]: Key \"%.*s\", Value %llu", node_off,
511 		   cur_key, keylen, keybuf, *value);
512 
513 	brelse(this_node->bh);
514 	kfree(this_node);
515 
516 	befs_debug(sb, "<--- %s", __func__);
517 
518 	return BEFS_OK;
519 
520       error_alloc:
521 	kfree(this_node);
522 
523       error:
524 	*keysize = 0;
525 	*value = 0;
526 	befs_debug(sb, "<--- %s ERROR", __func__);
527 	return BEFS_ERR;
528 }
529 
530 /**
531  * befs_btree_seekleaf - Find the first leafnode in the btree
532  * @sb: Filesystem superblock
533  * @ds: Datastream containing btree
534  * @bt_super: Pointer to the superblock of the btree
535  * @this_node: Buffer to return the leafnode in
536  * @node_off: Pointer to offset of current node within datastream. Modified
537  * 		by the function.
538  *
539  * Helper function for btree traverse. Moves the current position to the
540  * start of the first leaf node.
541  *
542  * Also checks for an empty tree. If there are no keys, returns BEFS_BT_EMPTY.
543  */
544 static int
545 befs_btree_seekleaf(struct super_block *sb, const befs_data_stream *ds,
546 		    befs_btree_super *bt_super,
547 		    struct befs_btree_node *this_node,
548 		    befs_off_t * node_off)
549 {
550 
551 	befs_debug(sb, "---> %s", __func__);
552 
553 	if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
554 		befs_error(sb, "%s failed to read "
555 			   "node at %llu", __func__, *node_off);
556 		goto error;
557 	}
558 	befs_debug(sb, "Seekleaf to root node %llu", *node_off);
559 
560 	if (this_node->head.all_key_count == 0 && befs_leafnode(this_node)) {
561 		befs_debug(sb, "<--- %s Tree is EMPTY", __func__);
562 		return BEFS_BT_EMPTY;
563 	}
564 
565 	while (!befs_leafnode(this_node)) {
566 
567 		if (this_node->head.all_key_count == 0) {
568 			befs_debug(sb, "%s encountered "
569 				   "an empty interior node: %llu. Using Overflow "
570 				   "node: %llu", __func__, *node_off,
571 				   this_node->head.overflow);
572 			*node_off = this_node->head.overflow;
573 		} else {
574 			fs64 *valarray = befs_bt_valarray(this_node);
575 			*node_off = fs64_to_cpu(sb, valarray[0]);
576 		}
577 		if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
578 			befs_error(sb, "%s failed to read "
579 				   "node at %llu", __func__, *node_off);
580 			goto error;
581 		}
582 
583 		befs_debug(sb, "Seekleaf to child node %llu", *node_off);
584 	}
585 	befs_debug(sb, "Node %llu is a leaf node", *node_off);
586 
587 	return BEFS_OK;
588 
589       error:
590 	befs_debug(sb, "<--- %s ERROR", __func__);
591 	return BEFS_ERR;
592 }
593 
594 /**
595  * befs_leafnode - Determine if the btree node is a leaf node or an
596  * interior node
597  * @node: Pointer to node structure to test
598  *
599  * Return 1 if leaf, 0 if interior
600  */
601 static int
602 befs_leafnode(struct befs_btree_node *node)
603 {
604 	/* all interior nodes (and only interior nodes) have an overflow node */
605 	if (node->head.overflow == BEFS_BT_INVAL)
606 		return 1;
607 	else
608 		return 0;
609 }
610 
611 /**
612  * befs_bt_keylen_index - Finds start of keylen index in a node
613  * @node: Pointer to the node structure to find the keylen index within
614  *
615  * Returns a pointer to the start of the key length index array
616  * of the B+tree node *@node
617  *
618  * "The length of all the keys in the node is added to the size of the
619  * header and then rounded up to a multiple of four to get the beginning
620  * of the key length index" (p.88, practical filesystem design).
621  *
622  * Except that rounding up to 8 works, and rounding up to 4 doesn't.
623  */
624 static fs16 *
625 befs_bt_keylen_index(struct befs_btree_node *node)
626 {
627 	const int keylen_align = 8;
628 	unsigned long int off =
629 	    (sizeof (befs_btree_nodehead) + node->head.all_key_length);
630 	ulong tmp = off % keylen_align;
631 
632 	if (tmp)
633 		off += keylen_align - tmp;
634 
635 	return (fs16 *) ((void *) node->od_node + off);
636 }
637 
638 /**
639  * befs_bt_valarray - Finds the start of value array in a node
640  * @node: Pointer to the node structure to find the value array within
641  *
642  * Returns a pointer to the start of the value array
643  * of the node pointed to by the node header
644  */
645 static fs64 *
646 befs_bt_valarray(struct befs_btree_node *node)
647 {
648 	void *keylen_index_start = (void *) befs_bt_keylen_index(node);
649 	size_t keylen_index_size = node->head.all_key_count * sizeof (fs16);
650 
651 	return (fs64 *) (keylen_index_start + keylen_index_size);
652 }
653 
654 /**
655  * befs_bt_keydata - Finds start of keydata array in a node
656  * @node: Pointer to the node structure to find the keydata array within
657  *
658  * Returns a pointer to the start of the keydata array
659  * of the node pointed to by the node header
660  */
661 static char *
662 befs_bt_keydata(struct befs_btree_node *node)
663 {
664 	return (char *) ((void *) node->od_node + sizeof (befs_btree_nodehead));
665 }
666 
667 /**
668  * befs_bt_get_key - returns a pointer to the start of a key
669  * @sb: filesystem superblock
670  * @node: node in which to look for the key
671  * @index: the index of the key to get
672  * @keylen: modified to be the length of the key at @index
673  *
674  * Returns a valid pointer into @node on success.
675  * Returns NULL on failure (bad input) and sets *@keylen = 0
676  */
677 static char *
678 befs_bt_get_key(struct super_block *sb, struct befs_btree_node *node,
679 		int index, u16 * keylen)
680 {
681 	int prev_key_end;
682 	char *keystart;
683 	fs16 *keylen_index;
684 
685 	if (index < 0 || index > node->head.all_key_count) {
686 		*keylen = 0;
687 		return NULL;
688 	}
689 
690 	keystart = befs_bt_keydata(node);
691 	keylen_index = befs_bt_keylen_index(node);
692 
693 	if (index == 0)
694 		prev_key_end = 0;
695 	else
696 		prev_key_end = fs16_to_cpu(sb, keylen_index[index - 1]);
697 
698 	*keylen = fs16_to_cpu(sb, keylen_index[index]) - prev_key_end;
699 
700 	return keystart + prev_key_end;
701 }
702 
703 /**
704  * befs_compare_strings - compare two strings
705  * @key1: pointer to the first key to be compared
706  * @keylen1: length in bytes of key1
707  * @key2: pointer to the second key to be compared
708  * @keylen2: length in bytes of key2
709  *
710  * Returns 0 if @key1 and @key2 are equal.
711  * Returns >0 if @key1 is greater.
712  * Returns <0 if @key2 is greater.
713  */
714 static int
715 befs_compare_strings(const void *key1, int keylen1,
716 		     const void *key2, int keylen2)
717 {
718 	int len = min_t(int, keylen1, keylen2);
719 	int result = strncmp(key1, key2, len);
720 	if (result == 0)
721 		result = keylen1 - keylen2;
722 	return result;
723 }
724 
725 /* These will be used for non-string keyed btrees */
726 #if 0
727 static int
728 btree_compare_int32(cont void *key1, int keylen1, const void *key2, int keylen2)
729 {
730 	return *(int32_t *) key1 - *(int32_t *) key2;
731 }
732 
733 static int
734 btree_compare_uint32(cont void *key1, int keylen1,
735 		     const void *key2, int keylen2)
736 {
737 	if (*(u_int32_t *) key1 == *(u_int32_t *) key2)
738 		return 0;
739 	else if (*(u_int32_t *) key1 > *(u_int32_t *) key2)
740 		return 1;
741 
742 	return -1;
743 }
744 static int
745 btree_compare_int64(cont void *key1, int keylen1, const void *key2, int keylen2)
746 {
747 	if (*(int64_t *) key1 == *(int64_t *) key2)
748 		return 0;
749 	else if (*(int64_t *) key1 > *(int64_t *) key2)
750 		return 1;
751 
752 	return -1;
753 }
754 
755 static int
756 btree_compare_uint64(cont void *key1, int keylen1,
757 		     const void *key2, int keylen2)
758 {
759 	if (*(u_int64_t *) key1 == *(u_int64_t *) key2)
760 		return 0;
761 	else if (*(u_int64_t *) key1 > *(u_int64_t *) key2)
762 		return 1;
763 
764 	return -1;
765 }
766 
767 static int
768 btree_compare_float(cont void *key1, int keylen1, const void *key2, int keylen2)
769 {
770 	float result = *(float *) key1 - *(float *) key2;
771 	if (result == 0.0f)
772 		return 0;
773 
774 	return (result < 0.0f) ? -1 : 1;
775 }
776 
777 static int
778 btree_compare_double(cont void *key1, int keylen1,
779 		     const void *key2, int keylen2)
780 {
781 	double result = *(double *) key1 - *(double *) key2;
782 	if (result == 0.0)
783 		return 0;
784 
785 	return (result < 0.0) ? -1 : 1;
786 }
787 #endif				//0
788