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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 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, "---> befs_btree_read_super()");
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, "<--- befs_btree_read_super()");
166         return BEFS_OK;
167 
168       error:
169         befs_debug(sb, "<--- befs_btree_read_super() ERROR");
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, "---> befs_bt_read_node()");
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, "befs_bt_read_node() failed to read "
206                            "node at %Lu", node_off);
207                 befs_debug(sb, "<--- befs_bt_read_node() ERROR");
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, "<--- befs_btree_read_node()");
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, "---> befs_btree_find() Key: %s", 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 %u "
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 %Lu", 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 %Lu", 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, "<--- befs_btree_find() Key %s not found", key);
302                 *value = 0;
303                 return BEFS_BT_NOT_FOUND;
304         }
305         befs_debug(sb, "<--- befs_btree_find() Found key %s, value %Lu",
306                    key, *value);
307         return BEFS_OK;
308 
309       error_alloc:
310         kfree(this_node);
311       error:
312         *value = 0;
313         befs_debug(sb, "<--- befs_btree_find() ERROR");
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, "---> befs_find_key() %s", 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, "<--- befs_find_key() %s not found", 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, "<--- befs_find_key() found %s at %d",
377                                    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, "<--- befs_find_key() found %s at %d", 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, "---> befs_btree_read()");
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 %u "
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, "<--- befs_btree_read() Tree is EMPTY");
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                                    "<--- befs_btree_read() END of keys at %Lu",
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, "befs_btree_read() failed to read "
482                                    "node at %Lu", 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 [%Lu,%d]: keysize %d", node_off, cur_key, keylen);
496 
497         if (bufsize < keylen + 1) {
498                 befs_error(sb, "befs_btree_read() keybuf too small (%u) "
499                            "for key of size %d", bufsize, keylen);
500                 brelse(this_node->bh);
501                 goto error_alloc;
502         };
503 
504         strncpy(keybuf, keystart, keylen);
505         *value = fs64_to_cpu(sb, valarray[cur_key]);
506         *keysize = keylen;
507         keybuf[keylen] = '\0';
508 
509         befs_debug(sb, "Read [%Lu,%d]: Key \"%.*s\", Value %Lu", node_off,
510                    cur_key, keylen, keybuf, *value);
511 
512         brelse(this_node->bh);
513         kfree(this_node);
514 
515         befs_debug(sb, "<--- befs_btree_read()");
516 
517         return BEFS_OK;
518 
519       error_alloc:
520         kfree(this_node);
521 
522       error:
523         *keysize = 0;
524         *value = 0;
525         befs_debug(sb, "<--- befs_btree_read() ERROR");
526         return BEFS_ERR;
527 }
528 
529 /**
530  * befs_btree_seekleaf - Find the first leafnode in the btree
531  * @sb: Filesystem superblock
532  * @ds: Datastream containing btree
533  * @bt_super: Pointer to the superblock of the btree
534  * @this_node: Buffer to return the leafnode in
535  * @node_off: Pointer to offset of current node within datastream. Modified
536  *              by the function.
537  *
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, befs_data_stream * ds,
546                     befs_btree_super * bt_super, befs_btree_node * this_node,
547                     befs_off_t * node_off)
548 {
549 
550         befs_debug(sb, "---> befs_btree_seekleaf()");
551 
552         if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
553                 befs_error(sb, "befs_btree_seekleaf() failed to read "
554                            "node at %Lu", *node_off);
555                 goto error;
556         }
557         befs_debug(sb, "Seekleaf to root node %Lu", *node_off);
558 
559         if (this_node->head.all_key_count == 0 && befs_leafnode(this_node)) {
560                 befs_debug(sb, "<--- befs_btree_seekleaf() Tree is EMPTY");
561                 return BEFS_BT_EMPTY;
562         }
563 
564         while (!befs_leafnode(this_node)) {
565 
566                 if (this_node->head.all_key_count == 0) {
567                         befs_debug(sb, "befs_btree_seekleaf() encountered "
568                                    "an empty interior node: %Lu. Using Overflow "
569                                    "node: %Lu", *node_off,
570                                    this_node->head.overflow);
571                         *node_off = this_node->head.overflow;
572                 } else {
573                         fs64 *valarray = befs_bt_valarray(this_node);
574                         *node_off = fs64_to_cpu(sb, valarray[0]);
575                 }
576                 if (befs_bt_read_node(sb, ds, this_node, *node_off) != BEFS_OK) {
577                         befs_error(sb, "befs_btree_seekleaf() failed to read "
578                                    "node at %Lu", *node_off);
579                         goto error;
580                 }
581 
582                 befs_debug(sb, "Seekleaf to child node %Lu", *node_off);
583         }
584         befs_debug(sb, "Node %Lu is a leaf node", *node_off);
585 
586         return BEFS_OK;
587 
588       error:
589         befs_debug(sb, "<--- befs_btree_seekleaf() ERROR");
590         return BEFS_ERR;
591 }
592 
593 /**
594  * befs_leafnode - Determine if the btree node is a leaf node or an 
595  * interior node
596  * @node: Pointer to node structure to test
597  * 
598  * Return 1 if leaf, 0 if interior
599  */
600 static int
601 befs_leafnode(befs_btree_node * node)
602 {
603         /* all interior nodes (and only interior nodes) have an overflow node */
604         if (node->head.overflow == befs_bt_inval)
605                 return 1;
606         else
607                 return 0;
608 }
609 
610 /**
611  * befs_bt_keylen_index - Finds start of keylen index in a node
612  * @node: Pointer to the node structure to find the keylen index within
613  *
614  * Returns a pointer to the start of the key length index array
615  * of the B+tree node *@node
616  *
617  * "The length of all the keys in the node is added to the size of the
618  * header and then rounded up to a multiple of four to get the beginning
619  * of the key length index" (p.88, practical filesystem design).
620  *
621  * Except that rounding up to 8 works, and rounding up to 4 doesn't.
622  */
623 static fs16 *
624 befs_bt_keylen_index(befs_btree_node * node)
625 {
626         const int keylen_align = 8;
627         unsigned long int off =
628             (sizeof (befs_btree_nodehead) + node->head.all_key_length);
629         ulong tmp = off % keylen_align;
630 
631         if (tmp)
632                 off += keylen_align - tmp;
633 
634         return (fs16 *) ((void *) node->od_node + off);
635 }
636 
637 /**
638  * befs_bt_valarray - Finds the start of value array in a node
639  * @node: Pointer to the node structure to find the value array within
640  *
641  * Returns a pointer to the start of the value array
642  * of the node pointed to by the node header
643  */
644 static fs64 *
645 befs_bt_valarray(befs_btree_node * node)
646 {
647         void *keylen_index_start = (void *) befs_bt_keylen_index(node);
648         size_t keylen_index_size = node->head.all_key_count * sizeof (fs16);
649 
650         return (fs64 *) (keylen_index_start + keylen_index_size);
651 }
652 
653 /**
654  * befs_bt_keydata - Finds start of keydata array in a node
655  * @node: Pointer to the node structure to find the keydata array within
656  *
657  * Returns a pointer to the start of the keydata array
658  * of the node pointed to by the node header 
659  */
660 static char *
661 befs_bt_keydata(befs_btree_node * node)
662 {
663         return (char *) ((void *) node->od_node + sizeof (befs_btree_nodehead));
664 }
665 
666 /**
667  * befs_bt_get_key - returns a pointer to the start of a key
668  * @sb: filesystem superblock
669  * @node: node in which to look for the key
670  * @index: the index of the key to get
671  * @keylen: modified to be the length of the key at @index
672  *
673  * Returns a valid pointer into @node on success.
674  * Returns NULL on failure (bad input) and sets *@keylen = 0
675  */
676 static char *
677 befs_bt_get_key(struct super_block *sb, befs_btree_node * node,
678                 int index, u16 * keylen)
679 {
680         int prev_key_end;
681         char *keystart;
682         fs16 *keylen_index;
683 
684         if (index < 0 || index > node->head.all_key_count) {
685                 *keylen = 0;
686                 return NULL;
687         }
688 
689         keystart = befs_bt_keydata(node);
690         keylen_index = befs_bt_keylen_index(node);
691 
692         if (index == 0)
693                 prev_key_end = 0;
694         else
695                 prev_key_end = fs16_to_cpu(sb, keylen_index[index - 1]);
696 
697         *keylen = fs16_to_cpu(sb, keylen_index[index]) - prev_key_end;
698 
699         return keystart + prev_key_end;
700 }
701 
702 /**
703  * befs_compare_strings - compare two strings
704  * @key1: pointer to the first key to be compared 
705  * @keylen1: length in bytes of key1
706  * @key2: pointer to the second key to be compared
707  * @kelen2: length in bytes of key2
708  *
709  * Returns 0 if @key1 and @key2 are equal.
710  * Returns >0 if @key1 is greater.
711  * Returns <0 if @key2 is greater..
712  */
713 static int
714 befs_compare_strings(const void *key1, int keylen1,
715                      const void *key2, int keylen2)
716 {
717         int len = min_t(int, keylen1, keylen2);
718         int result = strncmp(key1, key2, len);
719         if (result == 0)
720                 result = keylen1 - keylen2;
721         return result;
722 }
723 
724 /* These will be used for non-string keyed btrees */
725 #if 0
726 static int
727 btree_compare_int32(cont void *key1, int keylen1, const void *key2, int keylen2)
728 {
729         return *(int32_t *) key1 - *(int32_t *) key2;
730 }
731 
732 static int
733 btree_compare_uint32(cont void *key1, int keylen1,
734                      const void *key2, int keylen2)
735 {
736         if (*(u_int32_t *) key1 == *(u_int32_t *) key2)
737                 return 0;
738         else if (*(u_int32_t *) key1 > *(u_int32_t *) key2)
739                 return 1;
740 
741         return -1;
742 }
743 static int
744 btree_compare_int64(cont void *key1, int keylen1, const void *key2, int keylen2)
745 {
746         if (*(int64_t *) key1 == *(int64_t *) key2)
747                 return 0;
748         else if (*(int64_t *) key1 > *(int64_t *) key2)
749                 return 1;
750 
751         return -1;
752 }
753 
754 static int
755 btree_compare_uint64(cont void *key1, int keylen1,
756                      const void *key2, int keylen2)
757 {
758         if (*(u_int64_t *) key1 == *(u_int64_t *) key2)
759                 return 0;
760         else if (*(u_int64_t *) key1 > *(u_int64_t *) key2)
761                 return 1;
762 
763         return -1;
764 }
765 
766 static int
767 btree_compare_float(cont void *key1, int keylen1, const void *key2, int keylen2)
768 {
769         float result = *(float *) key1 - *(float *) key2;
770         if (result == 0.0f)
771                 return 0;
772 
773         return (result < 0.0f) ? -1 : 1;
774 }
775 
776 static int
777 btree_compare_double(cont void *key1, int keylen1,
778                      const void *key2, int keylen2)
779 {
780         double result = *(double *) key1 - *(double *) key2;
781         if (result == 0.0)
782                 return 0;
783 
784         return (result < 0.0) ? -1 : 1;
785 }
786 #endif                          //
787 

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