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Linux/fs/befs/btree.c

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

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