xref: /openbmc/linux/fs/befs/btree.c (revision b34e08d5)
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 typedef struct {
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 } befs_btree_node;
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, befs_data_stream * ds,
92 			       befs_btree_super * bt_super,
93 			       befs_btree_node * this_node,
94 			       befs_off_t * node_off);
95 
96 static int befs_bt_read_super(struct super_block *sb, befs_data_stream * ds,
97 			      befs_btree_super * sup);
98 
99 static int befs_bt_read_node(struct super_block *sb, befs_data_stream * ds,
100 			     befs_btree_node * node, befs_off_t node_off);
101 
102 static int befs_leafnode(befs_btree_node * node);
103 
104 static fs16 *befs_bt_keylen_index(befs_btree_node * node);
105 
106 static fs64 *befs_bt_valarray(befs_btree_node * node);
107 
108 static char *befs_bt_keydata(befs_btree_node * node);
109 
110 static int befs_find_key(struct super_block *sb, befs_btree_node * node,
111 			 const char *findkey, befs_off_t * value);
112 
113 static char *befs_bt_get_key(struct super_block *sb, befs_btree_node * node,
114 			     int index, u16 * keylen);
115 
116 static int befs_compare_strings(const void *key1, int keylen1,
117 				const void *key2, int keylen2);
118 
119 /**
120  * befs_bt_read_super - read in btree superblock convert to cpu byteorder
121  * @sb: Filesystem superblock
122  * @ds: Datastream to read from
123  * @sup: Buffer in which to place the btree superblock
124  *
125  * Calls befs_read_datastream to read in the btree superblock and
126  * makes sure it is in cpu byteorder, byteswapping if necessary.
127  *
128  * On success, returns BEFS_OK and *@sup contains the btree superblock,
129  * in cpu byte order.
130  *
131  * On failure, BEFS_ERR is returned.
132  */
133 static int
134 befs_bt_read_super(struct super_block *sb, befs_data_stream * ds,
135 		   befs_btree_super * sup)
136 {
137 	struct buffer_head *bh = NULL;
138 	befs_disk_btree_super *od_sup = NULL;
139 
140 	befs_debug(sb, "---> %s", __func__);
141 
142 	bh = befs_read_datastream(sb, ds, 0, NULL);
143 
144 	if (!bh) {
145 		befs_error(sb, "Couldn't read index header.");
146 		goto error;
147 	}
148 	od_sup = (befs_disk_btree_super *) bh->b_data;
149 	befs_dump_index_entry(sb, od_sup);
150 
151 	sup->magic = fs32_to_cpu(sb, od_sup->magic);
152 	sup->node_size = fs32_to_cpu(sb, od_sup->node_size);
153 	sup->max_depth = fs32_to_cpu(sb, od_sup->max_depth);
154 	sup->data_type = fs32_to_cpu(sb, od_sup->data_type);
155 	sup->root_node_ptr = fs64_to_cpu(sb, od_sup->root_node_ptr);
156 	sup->free_node_ptr = fs64_to_cpu(sb, od_sup->free_node_ptr);
157 	sup->max_size = fs64_to_cpu(sb, od_sup->max_size);
158 
159 	brelse(bh);
160 	if (sup->magic != BEFS_BTREE_MAGIC) {
161 		befs_error(sb, "Index header has bad magic.");
162 		goto error;
163 	}
164 
165 	befs_debug(sb, "<--- %s", __func__);
166 	return BEFS_OK;
167 
168       error:
169 	befs_debug(sb, "<--- %s ERROR", __func__);
170 	return BEFS_ERR;
171 }
172 
173 /**
174  * befs_bt_read_node - read in btree node and convert to cpu byteorder
175  * @sb: Filesystem superblock
176  * @ds: Datastream to read from
177  * @node: Buffer in which to place the btree node
178  * @node_off: Starting offset (in bytes) of the node in @ds
179  *
180  * Calls befs_read_datastream to read in the indicated btree node and
181  * makes sure its header fields are in cpu byteorder, byteswapping if
182  * necessary.
183  * Note: node->bh must be NULL when this function called first
184  * time. Don't forget brelse(node->bh) after last call.
185  *
186  * On success, returns BEFS_OK and *@node contains the btree node that
187  * starts at @node_off, with the node->head fields in cpu byte order.
188  *
189  * On failure, BEFS_ERR is returned.
190  */
191 
192 static int
193 befs_bt_read_node(struct super_block *sb, befs_data_stream * ds,
194 		  befs_btree_node * node, befs_off_t node_off)
195 {
196 	uint off = 0;
197 
198 	befs_debug(sb, "---> %s", __func__);
199 
200 	if (node->bh)
201 		brelse(node->bh);
202 
203 	node->bh = befs_read_datastream(sb, ds, node_off, &off);
204 	if (!node->bh) {
205 		befs_error(sb, "%s failed to read "
206 			   "node at %llu", __func__, node_off);
207 		befs_debug(sb, "<--- %s ERROR", __func__);
208 
209 		return BEFS_ERR;
210 	}
211 	node->od_node =
212 	    (befs_btree_nodehead *) ((void *) node->bh->b_data + off);
213 
214 	befs_dump_index_node(sb, node->od_node);
215 
216 	node->head.left = fs64_to_cpu(sb, node->od_node->left);
217 	node->head.right = fs64_to_cpu(sb, node->od_node->right);
218 	node->head.overflow = fs64_to_cpu(sb, node->od_node->overflow);
219 	node->head.all_key_count =
220 	    fs16_to_cpu(sb, node->od_node->all_key_count);
221 	node->head.all_key_length =
222 	    fs16_to_cpu(sb, node->od_node->all_key_length);
223 
224 	befs_debug(sb, "<--- %s", __func__);
225 	return BEFS_OK;
226 }
227 
228 /**
229  * befs_btree_find - Find a key in a befs B+tree
230  * @sb: Filesystem superblock
231  * @ds: Datastream containing btree
232  * @key: Key string to lookup in btree
233  * @value: Value stored with @key
234  *
235  * On success, returns BEFS_OK and sets *@value to the value stored
236  * with @key (usually the disk block number of an inode).
237  *
238  * On failure, returns BEFS_ERR or BEFS_BT_NOT_FOUND.
239  *
240  * Algorithm:
241  *   Read the superblock and rootnode of the b+tree.
242  *   Drill down through the interior nodes using befs_find_key().
243  *   Once at the correct leaf node, use befs_find_key() again to get the
244  *   actuall value stored with the key.
245  */
246 int
247 befs_btree_find(struct super_block *sb, befs_data_stream * ds,
248 		const char *key, befs_off_t * value)
249 {
250 	befs_btree_node *this_node = NULL;
251 	befs_btree_super bt_super;
252 	befs_off_t node_off;
253 	int res;
254 
255 	befs_debug(sb, "---> %s Key: %s", __func__, key);
256 
257 	if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {
258 		befs_error(sb,
259 			   "befs_btree_find() failed to read index superblock");
260 		goto error;
261 	}
262 
263 	this_node = kmalloc(sizeof (befs_btree_node),
264 						GFP_NOFS);
265 	if (!this_node) {
266 		befs_error(sb, "befs_btree_find() failed to allocate %zu "
267 			   "bytes of memory", sizeof (befs_btree_node));
268 		goto error;
269 	}
270 
271 	this_node->bh = NULL;
272 
273 	/* read in root node */
274 	node_off = bt_super.root_node_ptr;
275 	if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
276 		befs_error(sb, "befs_btree_find() failed to read "
277 			   "node at %llu", node_off);
278 		goto error_alloc;
279 	}
280 
281 	while (!befs_leafnode(this_node)) {
282 		res = befs_find_key(sb, this_node, key, &node_off);
283 		if (res == BEFS_BT_NOT_FOUND)
284 			node_off = this_node->head.overflow;
285 		/* if no match, go to overflow node */
286 		if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
287 			befs_error(sb, "befs_btree_find() failed to read "
288 				   "node at %llu", node_off);
289 			goto error_alloc;
290 		}
291 	}
292 
293 	/* at the correct leaf node now */
294 
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_debug(sb, "<--- %s Key %s not found", __func__, key);
302 		*value = 0;
303 		return BEFS_BT_NOT_FOUND;
304 	}
305 	befs_debug(sb, "<--- %s Found key %s, value %llu", __func__,
306 		   key, *value);
307 	return BEFS_OK;
308 
309       error_alloc:
310 	kfree(this_node);
311       error:
312 	*value = 0;
313 	befs_debug(sb, "<--- %s ERROR", __func__);
314 	return BEFS_ERR;
315 }
316 
317 /**
318  * befs_find_key - Search for a key within a node
319  * @sb: Filesystem superblock
320  * @node: Node to find the key within
321  * @key: Keystring to search for
322  * @value: If key is found, the value stored with the key is put here
323  *
324  * finds exact match if one exists, and returns BEFS_BT_MATCH
325  * If no exact match, finds first key in node that is greater
326  * (alphabetically) than the search key and returns BEFS_BT_PARMATCH
327  * (for partial match, I guess). Can you think of something better to
328  * call it?
329  *
330  * If no key was a match or greater than the search key, return
331  * BEFS_BT_NOT_FOUND.
332  *
333  * Use binary search instead of a linear.
334  */
335 static int
336 befs_find_key(struct super_block *sb, befs_btree_node * node,
337 	      const char *findkey, befs_off_t * value)
338 {
339 	int first, last, mid;
340 	int eq;
341 	u16 keylen;
342 	int findkey_len;
343 	char *thiskey;
344 	fs64 *valarray;
345 
346 	befs_debug(sb, "---> %s %s", __func__, findkey);
347 
348 	*value = 0;
349 
350 	findkey_len = strlen(findkey);
351 
352 	/* if node can not contain key, just skeep this node */
353 	last = node->head.all_key_count - 1;
354 	thiskey = befs_bt_get_key(sb, node, last, &keylen);
355 
356 	eq = befs_compare_strings(thiskey, keylen, findkey, findkey_len);
357 	if (eq < 0) {
358 		befs_debug(sb, "<--- %s %s not found", __func__, findkey);
359 		return BEFS_BT_NOT_FOUND;
360 	}
361 
362 	valarray = befs_bt_valarray(node);
363 
364 	/* simple binary search */
365 	first = 0;
366 	mid = 0;
367 	while (last >= first) {
368 		mid = (last + first) / 2;
369 		befs_debug(sb, "first: %d, last: %d, mid: %d", first, last,
370 			   mid);
371 		thiskey = befs_bt_get_key(sb, node, mid, &keylen);
372 		eq = befs_compare_strings(thiskey, keylen, findkey,
373 					  findkey_len);
374 
375 		if (eq == 0) {
376 			befs_debug(sb, "<--- %s found %s at %d",
377 				   __func__, thiskey, mid);
378 
379 			*value = fs64_to_cpu(sb, valarray[mid]);
380 			return BEFS_BT_MATCH;
381 		}
382 		if (eq > 0)
383 			last = mid - 1;
384 		else
385 			first = mid + 1;
386 	}
387 	if (eq < 0)
388 		*value = fs64_to_cpu(sb, valarray[mid + 1]);
389 	else
390 		*value = fs64_to_cpu(sb, valarray[mid]);
391 	befs_debug(sb, "<--- %s found %s at %d", __func__, thiskey, mid);
392 	return BEFS_BT_PARMATCH;
393 }
394 
395 /**
396  * befs_btree_read - Traverse leafnodes of a btree
397  * @sb: Filesystem superblock
398  * @ds: Datastream containing btree
399  * @key_no: Key number (alphabetical order) of key to read
400  * @bufsize: Size of the buffer to return key in
401  * @keybuf: Pointer to a buffer to put the key in
402  * @keysize: Length of the returned key
403  * @value: Value stored with the returned key
404  *
405  * Heres how it works: Key_no is the index of the key/value pair to
406  * return in keybuf/value.
407  * Bufsize is the size of keybuf (BEFS_NAME_LEN+1 is a good size). Keysize is
408  * the number of charecters in the key (just a convenience).
409  *
410  * Algorithm:
411  *   Get the first leafnode of the tree. See if the requested key is in that
412  *   node. If not, follow the node->right link to the next leafnode. Repeat
413  *   until the (key_no)th key is found or the tree is out of keys.
414  */
415 int
416 befs_btree_read(struct super_block *sb, befs_data_stream * ds,
417 		loff_t key_no, size_t bufsize, char *keybuf, size_t * keysize,
418 		befs_off_t * value)
419 {
420 	befs_btree_node *this_node;
421 	befs_btree_super bt_super;
422 	befs_off_t node_off = 0;
423 	int cur_key;
424 	fs64 *valarray;
425 	char *keystart;
426 	u16 keylen;
427 	int res;
428 
429 	uint key_sum = 0;
430 
431 	befs_debug(sb, "---> %s", __func__);
432 
433 	if (befs_bt_read_super(sb, ds, &bt_super) != BEFS_OK) {
434 		befs_error(sb,
435 			   "befs_btree_read() failed to read index superblock");
436 		goto error;
437 	}
438 
439 	if ((this_node = kmalloc(sizeof (befs_btree_node), GFP_NOFS)) == NULL) {
440 		befs_error(sb, "befs_btree_read() failed to allocate %zu "
441 			   "bytes of memory", sizeof (befs_btree_node));
442 		goto error;
443 	}
444 
445 	node_off = bt_super.root_node_ptr;
446 	this_node->bh = NULL;
447 
448 	/* seeks down to first leafnode, reads it into this_node */
449 	res = befs_btree_seekleaf(sb, ds, &bt_super, this_node, &node_off);
450 	if (res == BEFS_BT_EMPTY) {
451 		brelse(this_node->bh);
452 		kfree(this_node);
453 		*value = 0;
454 		*keysize = 0;
455 		befs_debug(sb, "<--- %s Tree is EMPTY", __func__);
456 		return BEFS_BT_EMPTY;
457 	} else if (res == BEFS_ERR) {
458 		goto error_alloc;
459 	}
460 
461 	/* find the leaf node containing the key_no key */
462 
463 	while (key_sum + this_node->head.all_key_count <= key_no) {
464 
465 		/* no more nodes to look in: key_no is too large */
466 		if (this_node->head.right == befs_bt_inval) {
467 			*keysize = 0;
468 			*value = 0;
469 			befs_debug(sb,
470 				   "<--- %s END of keys at %llu", __func__,
471 				   (unsigned long long)
472 				   key_sum + this_node->head.all_key_count);
473 			brelse(this_node->bh);
474 			kfree(this_node);
475 			return BEFS_BT_END;
476 		}
477 
478 		key_sum += this_node->head.all_key_count;
479 		node_off = this_node->head.right;
480 
481 		if (befs_bt_read_node(sb, ds, this_node, node_off) != BEFS_OK) {
482 			befs_error(sb, "%s failed to read node at %llu",
483 				  __func__, (unsigned long long)node_off);
484 			goto error_alloc;
485 		}
486 	}
487 
488 	/* how many keys into this_node is key_no */
489 	cur_key = key_no - key_sum;
490 
491 	/* get pointers to datastructures within the node body */
492 	valarray = befs_bt_valarray(this_node);
493 
494 	keystart = befs_bt_get_key(sb, this_node, cur_key, &keylen);
495 
496 	befs_debug(sb, "Read [%llu,%d]: keysize %d",
497 		   (long long unsigned int)node_off, (int)cur_key,
498 		   (int)keylen);
499 
500 	if (bufsize < keylen + 1) {
501 		befs_error(sb, "%s keybuf too small (%zu) "
502 			   "for key of size %d", __func__, bufsize, keylen);
503 		brelse(this_node->bh);
504 		goto error_alloc;
505 	};
506 
507 	strncpy(keybuf, keystart, keylen);
508 	*value = fs64_to_cpu(sb, valarray[cur_key]);
509 	*keysize = keylen;
510 	keybuf[keylen] = '\0';
511 
512 	befs_debug(sb, "Read [%llu,%d]: Key \"%.*s\", Value %llu", node_off,
513 		   cur_key, keylen, keybuf, *value);
514 
515 	brelse(this_node->bh);
516 	kfree(this_node);
517 
518 	befs_debug(sb, "<--- %s", __func__);
519 
520 	return BEFS_OK;
521 
522       error_alloc:
523 	kfree(this_node);
524 
525       error:
526 	*keysize = 0;
527 	*value = 0;
528 	befs_debug(sb, "<--- %s ERROR", __func__);
529 	return BEFS_ERR;
530 }
531 
532 /**
533  * befs_btree_seekleaf - Find the first leafnode in the btree
534  * @sb: Filesystem superblock
535  * @ds: Datastream containing btree
536  * @bt_super: Pointer to the superblock of the btree
537  * @this_node: Buffer to return the leafnode in
538  * @node_off: Pointer to offset of current node within datastream. Modified
539  * 		by the function.
540  *
541  *
542  * Helper function for btree traverse. Moves the current position to the
543  * start of the first leaf node.
544  *
545  * Also checks for an empty tree. If there are no keys, returns BEFS_BT_EMPTY.
546  */
547 static int
548 befs_btree_seekleaf(struct super_block *sb, befs_data_stream * ds,
549 		    befs_btree_super * bt_super, befs_btree_node * this_node,
550 		    befs_off_t * node_off)
551 {
552 
553 	befs_debug(sb, "---> %s", __func__);
554 
555 	if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
556 		befs_error(sb, "%s failed to read "
557 			   "node at %llu", __func__, *node_off);
558 		goto error;
559 	}
560 	befs_debug(sb, "Seekleaf to root node %llu", *node_off);
561 
562 	if (this_node->head.all_key_count == 0 && befs_leafnode(this_node)) {
563 		befs_debug(sb, "<--- %s Tree is EMPTY", __func__);
564 		return BEFS_BT_EMPTY;
565 	}
566 
567 	while (!befs_leafnode(this_node)) {
568 
569 		if (this_node->head.all_key_count == 0) {
570 			befs_debug(sb, "%s encountered "
571 				   "an empty interior node: %llu. Using Overflow "
572 				   "node: %llu", __func__, *node_off,
573 				   this_node->head.overflow);
574 			*node_off = this_node->head.overflow;
575 		} else {
576 			fs64 *valarray = befs_bt_valarray(this_node);
577 			*node_off = fs64_to_cpu(sb, valarray[0]);
578 		}
579 		if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
580 			befs_error(sb, "%s failed to read "
581 				   "node at %llu", __func__, *node_off);
582 			goto error;
583 		}
584 
585 		befs_debug(sb, "Seekleaf to child node %llu", *node_off);
586 	}
587 	befs_debug(sb, "Node %llu is a leaf node", *node_off);
588 
589 	return BEFS_OK;
590 
591       error:
592 	befs_debug(sb, "<--- %s ERROR", __func__);
593 	return BEFS_ERR;
594 }
595 
596 /**
597  * befs_leafnode - Determine if the btree node is a leaf node or an
598  * interior node
599  * @node: Pointer to node structure to test
600  *
601  * Return 1 if leaf, 0 if interior
602  */
603 static int
604 befs_leafnode(befs_btree_node * node)
605 {
606 	/* all interior nodes (and only interior nodes) have an overflow node */
607 	if (node->head.overflow == befs_bt_inval)
608 		return 1;
609 	else
610 		return 0;
611 }
612 
613 /**
614  * befs_bt_keylen_index - Finds start of keylen index in a node
615  * @node: Pointer to the node structure to find the keylen index within
616  *
617  * Returns a pointer to the start of the key length index array
618  * of the B+tree node *@node
619  *
620  * "The length of all the keys in the node is added to the size of the
621  * header and then rounded up to a multiple of four to get the beginning
622  * of the key length index" (p.88, practical filesystem design).
623  *
624  * Except that rounding up to 8 works, and rounding up to 4 doesn't.
625  */
626 static fs16 *
627 befs_bt_keylen_index(befs_btree_node * node)
628 {
629 	const int keylen_align = 8;
630 	unsigned long int off =
631 	    (sizeof (befs_btree_nodehead) + node->head.all_key_length);
632 	ulong tmp = off % keylen_align;
633 
634 	if (tmp)
635 		off += keylen_align - tmp;
636 
637 	return (fs16 *) ((void *) node->od_node + off);
638 }
639 
640 /**
641  * befs_bt_valarray - Finds the start of value array in a node
642  * @node: Pointer to the node structure to find the value array within
643  *
644  * Returns a pointer to the start of the value array
645  * of the node pointed to by the node header
646  */
647 static fs64 *
648 befs_bt_valarray(befs_btree_node * node)
649 {
650 	void *keylen_index_start = (void *) befs_bt_keylen_index(node);
651 	size_t keylen_index_size = node->head.all_key_count * sizeof (fs16);
652 
653 	return (fs64 *) (keylen_index_start + keylen_index_size);
654 }
655 
656 /**
657  * befs_bt_keydata - Finds start of keydata array in a node
658  * @node: Pointer to the node structure to find the keydata array within
659  *
660  * Returns a pointer to the start of the keydata array
661  * of the node pointed to by the node header
662  */
663 static char *
664 befs_bt_keydata(befs_btree_node * node)
665 {
666 	return (char *) ((void *) node->od_node + sizeof (befs_btree_nodehead));
667 }
668 
669 /**
670  * befs_bt_get_key - returns a pointer to the start of a key
671  * @sb: filesystem superblock
672  * @node: node in which to look for the key
673  * @index: the index of the key to get
674  * @keylen: modified to be the length of the key at @index
675  *
676  * Returns a valid pointer into @node on success.
677  * Returns NULL on failure (bad input) and sets *@keylen = 0
678  */
679 static char *
680 befs_bt_get_key(struct super_block *sb, befs_btree_node * node,
681 		int index, u16 * keylen)
682 {
683 	int prev_key_end;
684 	char *keystart;
685 	fs16 *keylen_index;
686 
687 	if (index < 0 || index > node->head.all_key_count) {
688 		*keylen = 0;
689 		return NULL;
690 	}
691 
692 	keystart = befs_bt_keydata(node);
693 	keylen_index = befs_bt_keylen_index(node);
694 
695 	if (index == 0)
696 		prev_key_end = 0;
697 	else
698 		prev_key_end = fs16_to_cpu(sb, keylen_index[index - 1]);
699 
700 	*keylen = fs16_to_cpu(sb, keylen_index[index]) - prev_key_end;
701 
702 	return keystart + prev_key_end;
703 }
704 
705 /**
706  * befs_compare_strings - compare two strings
707  * @key1: pointer to the first key to be compared
708  * @keylen1: length in bytes of key1
709  * @key2: pointer to the second key to be compared
710  * @kelen2: length in bytes of key2
711  *
712  * Returns 0 if @key1 and @key2 are equal.
713  * Returns >0 if @key1 is greater.
714  * Returns <0 if @key2 is greater..
715  */
716 static int
717 befs_compare_strings(const void *key1, int keylen1,
718 		     const void *key2, int keylen2)
719 {
720 	int len = min_t(int, keylen1, keylen2);
721 	int result = strncmp(key1, key2, len);
722 	if (result == 0)
723 		result = keylen1 - keylen2;
724 	return result;
725 }
726 
727 /* These will be used for non-string keyed btrees */
728 #if 0
729 static int
730 btree_compare_int32(cont void *key1, int keylen1, const void *key2, int keylen2)
731 {
732 	return *(int32_t *) key1 - *(int32_t *) key2;
733 }
734 
735 static int
736 btree_compare_uint32(cont void *key1, int keylen1,
737 		     const void *key2, int keylen2)
738 {
739 	if (*(u_int32_t *) key1 == *(u_int32_t *) key2)
740 		return 0;
741 	else if (*(u_int32_t *) key1 > *(u_int32_t *) key2)
742 		return 1;
743 
744 	return -1;
745 }
746 static int
747 btree_compare_int64(cont void *key1, int keylen1, const void *key2, int keylen2)
748 {
749 	if (*(int64_t *) key1 == *(int64_t *) key2)
750 		return 0;
751 	else if (*(int64_t *) key1 > *(int64_t *) key2)
752 		return 1;
753 
754 	return -1;
755 }
756 
757 static int
758 btree_compare_uint64(cont void *key1, int keylen1,
759 		     const void *key2, int keylen2)
760 {
761 	if (*(u_int64_t *) key1 == *(u_int64_t *) key2)
762 		return 0;
763 	else if (*(u_int64_t *) key1 > *(u_int64_t *) key2)
764 		return 1;
765 
766 	return -1;
767 }
768 
769 static int
770 btree_compare_float(cont void *key1, int keylen1, const void *key2, int keylen2)
771 {
772 	float result = *(float *) key1 - *(float *) key2;
773 	if (result == 0.0f)
774 		return 0;
775 
776 	return (result < 0.0f) ? -1 : 1;
777 }
778 
779 static int
780 btree_compare_double(cont void *key1, int keylen1,
781 		     const void *key2, int keylen2)
782 {
783 	double result = *(double *) key1 - *(double *) key2;
784 	if (result == 0.0)
785 		return 0;
786 
787 	return (result < 0.0) ? -1 : 1;
788 }
789 #endif				//0
790