1/* 2 * lib/btree.c - Simple In-memory B+Tree 3 * 4 * As should be obvious for Linux kernel code, license is GPLv2 5 * 6 * Copyright (c) 2007-2008 Joern Engel <joern@logfs.org> 7 * Bits and pieces stolen from Peter Zijlstra's code, which is 8 * Copyright 2007, Red Hat Inc. Peter Zijlstra <pzijlstr@redhat.com> 9 * GPLv2 10 * 11 * see http://programming.kicks-ass.net/kernel-patches/vma_lookup/btree.patch 12 * 13 * A relatively simple B+Tree implementation. I have written it as a learning 14 * excercise to understand how B+Trees work. Turned out to be useful as well. 15 * 16 * B+Trees can be used similar to Linux radix trees (which don't have anything 17 * in common with textbook radix trees, beware). Prerequisite for them working 18 * well is that access to a random tree node is much faster than a large number 19 * of operations within each node. 20 * 21 * Disks have fulfilled the prerequisite for a long time. More recently DRAM 22 * has gained similar properties, as memory access times, when measured in cpu 23 * cycles, have increased. Cacheline sizes have increased as well, which also 24 * helps B+Trees. 25 * 26 * Compared to radix trees, B+Trees are more efficient when dealing with a 27 * sparsely populated address space. Between 25% and 50% of the memory is 28 * occupied with valid pointers. When densely populated, radix trees contain 29 * ~98% pointers - hard to beat. Very sparse radix trees contain only ~2% 30 * pointers. 31 * 32 * This particular implementation stores pointers identified by a long value. 33 * Storing NULL pointers is illegal, lookup will return NULL when no entry 34 * was found. 35 * 36 * A tricks was used that is not commonly found in textbooks. The lowest 37 * values are to the right, not to the left. All used slots within a node 38 * are on the left, all unused slots contain NUL values. Most operations 39 * simply loop once over all slots and terminate on the first NUL. 40 */ 41 42#include <linux/btree.h> 43#include <linux/cache.h> 44#include <linux/kernel.h> 45#include <linux/slab.h> 46#include <linux/module.h> 47 48#define MAX(a, b) ((a) > (b) ? (a) : (b)) 49#define NODESIZE MAX(L1_CACHE_BYTES, 128) 50 51struct btree_geo { 52 int keylen; 53 int no_pairs; 54 int no_longs; 55}; 56 57struct btree_geo btree_geo32 = { 58 .keylen = 1, 59 .no_pairs = NODESIZE / sizeof(long) / 2, 60 .no_longs = NODESIZE / sizeof(long) / 2, 61}; 62EXPORT_SYMBOL_GPL(btree_geo32); 63 64#define LONG_PER_U64 (64 / BITS_PER_LONG) 65struct btree_geo btree_geo64 = { 66 .keylen = LONG_PER_U64, 67 .no_pairs = NODESIZE / sizeof(long) / (1 + LONG_PER_U64), 68 .no_longs = LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + LONG_PER_U64)), 69}; 70EXPORT_SYMBOL_GPL(btree_geo64); 71 72struct btree_geo btree_geo128 = { 73 .keylen = 2 * LONG_PER_U64, 74 .no_pairs = NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64), 75 .no_longs = 2 * LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64)), 76}; 77EXPORT_SYMBOL_GPL(btree_geo128); 78 79static struct kmem_cache *btree_cachep; 80 81void *btree_alloc(gfp_t gfp_mask, void *pool_data) 82{ 83 return kmem_cache_alloc(btree_cachep, gfp_mask); 84} 85EXPORT_SYMBOL_GPL(btree_alloc); 86 87void btree_free(void *element, void *pool_data) 88{ 89 kmem_cache_free(btree_cachep, element); 90} 91EXPORT_SYMBOL_GPL(btree_free); 92 93static unsigned long *btree_node_alloc(struct btree_head *head, gfp_t gfp) 94{ 95 unsigned long *node; 96 97 node = mempool_alloc(head->mempool, gfp); 98 if (likely(node)) 99 memset(node, 0, NODESIZE); 100 return node; 101} 102 103static int longcmp(const unsigned long *l1, const unsigned long *l2, size_t n) 104{ 105 size_t i; 106 107 for (i = 0; i < n; i++) { 108 if (l1[i] < l2[i]) 109 return -1; 110 if (l1[i] > l2[i]) 111 return 1; 112 } 113 return 0; 114} 115 116static unsigned long *longcpy(unsigned long *dest, const unsigned long *src, 117 size_t n) 118{ 119 size_t i; 120 121 for (i = 0; i < n; i++) 122 dest[i] = src[i]; 123 return dest; 124} 125 126static unsigned long *longset(unsigned long *s, unsigned long c, size_t n) 127{ 128 size_t i; 129 130 for (i = 0; i < n; i++) 131 s[i] = c; 132 return s; 133} 134 135static void dec_key(struct btree_geo *geo, unsigned long *key) 136{ 137 unsigned long val; 138 int i; 139 140 for (i = geo->keylen - 1; i >= 0; i--) { 141 val = key[i]; 142 key[i] = val - 1; 143 if (val) 144 break; 145 } 146} 147 148static unsigned long *bkey(struct btree_geo *geo, unsigned long *node, int n) 149{ 150 return &node[n * geo->keylen]; 151} 152 153static void *bval(struct btree_geo *geo, unsigned long *node, int n) 154{ 155 return (void *)node[geo->no_longs + n]; 156} 157 158static void setkey(struct btree_geo *geo, unsigned long *node, int n, 159 unsigned long *key) 160{ 161 longcpy(bkey(geo, node, n), key, geo->keylen); 162} 163 164static void setval(struct btree_geo *geo, unsigned long *node, int n, 165 void *val) 166{ 167 node[geo->no_longs + n] = (unsigned long) val; 168} 169 170static void clearpair(struct btree_geo *geo, unsigned long *node, int n) 171{ 172 longset(bkey(geo, node, n), 0, geo->keylen); 173 node[geo->no_longs + n] = 0; 174} 175 176static inline void __btree_init(struct btree_head *head) 177{ 178 head->node = NULL; 179 head->height = 0; 180} 181 182void btree_init_mempool(struct btree_head *head, mempool_t *mempool) 183{ 184 __btree_init(head); 185 head->mempool = mempool; 186} 187EXPORT_SYMBOL_GPL(btree_init_mempool); 188 189int btree_init(struct btree_head *head) 190{ 191 __btree_init(head); 192 head->mempool = mempool_create(0, btree_alloc, btree_free, NULL); 193 if (!head->mempool) 194 return -ENOMEM; 195 return 0; 196} 197EXPORT_SYMBOL_GPL(btree_init); 198 199void btree_destroy(struct btree_head *head) 200{ 201 mempool_destroy(head->mempool); 202 head->mempool = NULL; 203} 204EXPORT_SYMBOL_GPL(btree_destroy); 205 206void *btree_last(struct btree_head *head, struct btree_geo *geo, 207 unsigned long *key) 208{ 209 int height = head->height; 210 unsigned long *node = head->node; 211 212 if (height == 0) 213 return NULL; 214 215 for ( ; height > 1; height--) 216 node = bval(geo, node, 0); 217 218 longcpy(key, bkey(geo, node, 0), geo->keylen); 219 return bval(geo, node, 0); 220} 221EXPORT_SYMBOL_GPL(btree_last); 222 223static int keycmp(struct btree_geo *geo, unsigned long *node, int pos, 224 unsigned long *key) 225{ 226 return longcmp(bkey(geo, node, pos), key, geo->keylen); 227} 228 229static int keyzero(struct btree_geo *geo, unsigned long *key) 230{ 231 int i; 232 233 for (i = 0; i < geo->keylen; i++) 234 if (key[i]) 235 return 0; 236 237 return 1; 238} 239 240void *btree_lookup(struct btree_head *head, struct btree_geo *geo, 241 unsigned long *key) 242{ 243 int i, height = head->height; 244 unsigned long *node = head->node; 245 246 if (height == 0) 247 return NULL; 248 249 for ( ; height > 1; height--) { 250 for (i = 0; i < geo->no_pairs; i++) 251 if (keycmp(geo, node, i, key) <= 0) 252 break; 253 if (i == geo->no_pairs) 254 return NULL; 255 node = bval(geo, node, i); 256 if (!node) 257 return NULL; 258 } 259 260 if (!node) 261 return NULL; 262 263 for (i = 0; i < geo->no_pairs; i++) 264 if (keycmp(geo, node, i, key) == 0) 265 return bval(geo, node, i); 266 return NULL; 267} 268EXPORT_SYMBOL_GPL(btree_lookup); 269 270int btree_update(struct btree_head *head, struct btree_geo *geo, 271 unsigned long *key, void *val) 272{ 273 int i, height = head->height; 274 unsigned long *node = head->node; 275 276 if (height == 0) 277 return -ENOENT; 278 279 for ( ; height > 1; height--) { 280 for (i = 0; i < geo->no_pairs; i++) 281 if (keycmp(geo, node, i, key) <= 0) 282 break; 283 if (i == geo->no_pairs) 284 return -ENOENT; 285 node = bval(geo, node, i); 286 if (!node) 287 return -ENOENT; 288 } 289 290 if (!node) 291 return -ENOENT; 292 293 for (i = 0; i < geo->no_pairs; i++) 294 if (keycmp(geo, node, i, key) == 0) { 295 setval(geo, node, i, val); 296 return 0; 297 } 298 return -ENOENT; 299} 300EXPORT_SYMBOL_GPL(btree_update); 301 302/* 303 * Usually this function is quite similar to normal lookup. But the key of 304 * a parent node may be smaller than the smallest key of all its siblings. 305 * In such a case we cannot just return NULL, as we have only proven that no 306 * key smaller than __key, but larger than this parent key exists. 307 * So we set __key to the parent key and retry. We have to use the smallest 308 * such parent key, which is the last parent key we encountered. 309 */ 310void *btree_get_prev(struct btree_head *head, struct btree_geo *geo, 311 unsigned long *__key) 312{ 313 int i, height; 314 unsigned long *node, *oldnode; 315 unsigned long *retry_key = NULL, key[geo->keylen]; 316 317 if (keyzero(geo, __key)) 318 return NULL; 319 320 if (head->height == 0) 321 return NULL; 322retry: 323 longcpy(key, __key, geo->keylen); 324 dec_key(geo, key); 325 326 node = head->node; 327 for (height = head->height ; height > 1; height--) { 328 for (i = 0; i < geo->no_pairs; i++) 329 if (keycmp(geo, node, i, key) <= 0) 330 break; 331 if (i == geo->no_pairs) 332 goto miss; 333 oldnode = node; 334 node = bval(geo, node, i); 335 if (!node) 336 goto miss; 337 retry_key = bkey(geo, oldnode, i); 338 } 339 340 if (!node) 341 goto miss; 342 343 for (i = 0; i < geo->no_pairs; i++) { 344 if (keycmp(geo, node, i, key) <= 0) { 345 if (bval(geo, node, i)) { 346 longcpy(__key, bkey(geo, node, i), geo->keylen); 347 return bval(geo, node, i); 348 } else 349 goto miss; 350 } 351 } 352miss: 353 if (retry_key) { 354 __key = retry_key; 355 retry_key = NULL; 356 goto retry; 357 } 358 return NULL; 359} 360 361static int getpos(struct btree_geo *geo, unsigned long *node, 362 unsigned long *key) 363{ 364 int i; 365 366 for (i = 0; i < geo->no_pairs; i++) { 367 if (keycmp(geo, node, i, key) <= 0) 368 break; 369 } 370 return i; 371} 372 373static int getfill(struct btree_geo *geo, unsigned long *node, int start) 374{ 375 int i; 376 377 for (i = start; i < geo->no_pairs; i++) 378 if (!bval(geo, node, i)) 379 break; 380 return i; 381} 382 383/* 384 * locate the correct leaf node in the btree 385 */ 386static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo, 387 unsigned long *key, int level) 388{ 389 unsigned long *node = head->node; 390 int i, height; 391 392 for (height = head->height; height > level; height--) { 393 for (i = 0; i < geo->no_pairs; i++) 394 if (keycmp(geo, node, i, key) <= 0) 395 break; 396 397 if ((i == geo->no_pairs) || !bval(geo, node, i)) { 398 /* right-most key is too large, update it */ 399 i--; 400 setkey(geo, node, i, key); 401 } 402 BUG_ON(i < 0); 403 node = bval(geo, node, i); 404 } 405 BUG_ON(!node); 406 return node; 407} 408 409static int btree_grow(struct btree_head *head, struct btree_geo *geo, 410 gfp_t gfp) 411{ 412 unsigned long *node; 413 int fill; 414 415 node = btree_node_alloc(head, gfp); 416 if (!node) 417 return -ENOMEM; 418 if (head->node) { 419 fill = getfill(geo, head->node, 0); 420 setkey(geo, node, 0, bkey(geo, head->node, fill - 1)); 421 setval(geo, node, 0, head->node); 422 } 423 head->node = node; 424 head->height++; 425 return 0; 426} 427 428static void btree_shrink(struct btree_head *head, struct btree_geo *geo) 429{ 430 unsigned long *node; 431 int fill; 432 433 if (head->height <= 1) 434 return; 435 436 node = head->node; 437 fill = getfill(geo, node, 0); 438 BUG_ON(fill > 1); 439 head->node = bval(geo, node, 0); 440 head->height--; 441 mempool_free(node, head->mempool); 442} 443 444static int btree_insert_level(struct btree_head *head, struct btree_geo *geo, 445 unsigned long *key, void *val, int level, 446 gfp_t gfp) 447{ 448 unsigned long *node; 449 int i, pos, fill, err; 450 451 BUG_ON(!val); 452 if (head->height < level) { 453 err = btree_grow(head, geo, gfp); 454 if (err) 455 return err; 456 } 457 458retry: 459 node = find_level(head, geo, key, level); 460 pos = getpos(geo, node, key); 461 fill = getfill(geo, node, pos); 462 /* two identical keys are not allowed */ 463 BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0); 464 465 if (fill == geo->no_pairs) { 466 /* need to split node */ 467 unsigned long *new; 468 469 new = btree_node_alloc(head, gfp); 470 if (!new) 471 return -ENOMEM; 472 err = btree_insert_level(head, geo, 473 bkey(geo, node, fill / 2 - 1), 474 new, level + 1, gfp); 475 if (err) { 476 mempool_free(new, head->mempool); 477 return err; 478 } 479 for (i = 0; i < fill / 2; i++) { 480 setkey(geo, new, i, bkey(geo, node, i)); 481 setval(geo, new, i, bval(geo, node, i)); 482 setkey(geo, node, i, bkey(geo, node, i + fill / 2)); 483 setval(geo, node, i, bval(geo, node, i + fill / 2)); 484 clearpair(geo, node, i + fill / 2); 485 } 486 if (fill & 1) { 487 setkey(geo, node, i, bkey(geo, node, fill - 1)); 488 setval(geo, node, i, bval(geo, node, fill - 1)); 489 clearpair(geo, node, fill - 1); 490 } 491 goto retry; 492 } 493 BUG_ON(fill >= geo->no_pairs); 494 495 /* shift and insert */ 496 for (i = fill; i > pos; i--) { 497 setkey(geo, node, i, bkey(geo, node, i - 1)); 498 setval(geo, node, i, bval(geo, node, i - 1)); 499 } 500 setkey(geo, node, pos, key); 501 setval(geo, node, pos, val); 502 503 return 0; 504} 505 506int btree_insert(struct btree_head *head, struct btree_geo *geo, 507 unsigned long *key, void *val, gfp_t gfp) 508{ 509 return btree_insert_level(head, geo, key, val, 1, gfp); 510} 511EXPORT_SYMBOL_GPL(btree_insert); 512 513static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo, 514 unsigned long *key, int level); 515static void merge(struct btree_head *head, struct btree_geo *geo, int level, 516 unsigned long *left, int lfill, 517 unsigned long *right, int rfill, 518 unsigned long *parent, int lpos) 519{ 520 int i; 521 522 for (i = 0; i < rfill; i++) { 523 /* Move all keys to the left */ 524 setkey(geo, left, lfill + i, bkey(geo, right, i)); 525 setval(geo, left, lfill + i, bval(geo, right, i)); 526 } 527 /* Exchange left and right child in parent */ 528 setval(geo, parent, lpos, right); 529 setval(geo, parent, lpos + 1, left); 530 /* Remove left (formerly right) child from parent */ 531 btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1); 532 mempool_free(right, head->mempool); 533} 534 535static void rebalance(struct btree_head *head, struct btree_geo *geo, 536 unsigned long *key, int level, unsigned long *child, int fill) 537{ 538 unsigned long *parent, *left = NULL, *right = NULL; 539 int i, no_left, no_right; 540 541 if (fill == 0) { 542 /* Because we don't steal entries from a neigbour, this case 543 * can happen. Parent node contains a single child, this 544 * node, so merging with a sibling never happens. 545 */ 546 btree_remove_level(head, geo, key, level + 1); 547 mempool_free(child, head->mempool); 548 return; 549 } 550 551 parent = find_level(head, geo, key, level + 1); 552 i = getpos(geo, parent, key); 553 BUG_ON(bval(geo, parent, i) != child); 554 555 if (i > 0) { 556 left = bval(geo, parent, i - 1); 557 no_left = getfill(geo, left, 0); 558 if (fill + no_left <= geo->no_pairs) { 559 merge(head, geo, level, 560 left, no_left, 561 child, fill, 562 parent, i - 1); 563 return; 564 } 565 } 566 if (i + 1 < getfill(geo, parent, i)) { 567 right = bval(geo, parent, i + 1); 568 no_right = getfill(geo, right, 0); 569 if (fill + no_right <= geo->no_pairs) { 570 merge(head, geo, level, 571 child, fill, 572 right, no_right, 573 parent, i); 574 return; 575 } 576 } 577 /* 578 * We could also try to steal one entry from the left or right 579 * neighbor. By not doing so we changed the invariant from 580 * "all nodes are at least half full" to "no two neighboring 581 * nodes can be merged". Which means that the average fill of 582 * all nodes is still half or better. 583 */ 584} 585 586static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo, 587 unsigned long *key, int level) 588{ 589 unsigned long *node; 590 int i, pos, fill; 591 void *ret; 592 593 if (level > head->height) { 594 /* we recursed all the way up */ 595 head->height = 0; 596 head->node = NULL; 597 return NULL; 598 } 599 600 node = find_level(head, geo, key, level); 601 pos = getpos(geo, node, key); 602 fill = getfill(geo, node, pos); 603 if ((level == 1) && (keycmp(geo, node, pos, key) != 0)) 604 return NULL; 605 ret = bval(geo, node, pos); 606 607 /* remove and shift */ 608 for (i = pos; i < fill - 1; i++) { 609 setkey(geo, node, i, bkey(geo, node, i + 1)); 610 setval(geo, node, i, bval(geo, node, i + 1)); 611 } 612 clearpair(geo, node, fill - 1); 613 614 if (fill - 1 < geo->no_pairs / 2) { 615 if (level < head->height) 616 rebalance(head, geo, key, level, node, fill - 1); 617 else if (fill - 1 == 1) 618 btree_shrink(head, geo); 619 } 620 621 return ret; 622} 623 624void *btree_remove(struct btree_head *head, struct btree_geo *geo, 625 unsigned long *key) 626{ 627 if (head->height == 0) 628 return NULL; 629 630 return btree_remove_level(head, geo, key, 1); 631} 632EXPORT_SYMBOL_GPL(btree_remove); 633 634int btree_merge(struct btree_head *target, struct btree_head *victim, 635 struct btree_geo *geo, gfp_t gfp) 636{ 637 unsigned long key[geo->keylen]; 638 unsigned long dup[geo->keylen]; 639 void *val; 640 int err; 641 642 BUG_ON(target == victim); 643 644 if (!(target->node)) { 645 /* target is empty, just copy fields over */ 646 target->node = victim->node; 647 target->height = victim->height; 648 __btree_init(victim); 649 return 0; 650 } 651 652 /* TODO: This needs some optimizations. Currently we do three tree 653 * walks to remove a single object from the victim. 654 */ 655 for (;;) { 656 if (!btree_last(victim, geo, key)) 657 break; 658 val = btree_lookup(victim, geo, key); 659 err = btree_insert(target, geo, key, val, gfp); 660 if (err) 661 return err; 662 /* We must make a copy of the key, as the original will get 663 * mangled inside btree_remove. */ 664 longcpy(dup, key, geo->keylen); 665 btree_remove(victim, geo, dup); 666 } 667 return 0; 668} 669EXPORT_SYMBOL_GPL(btree_merge); 670 671static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo, 672 unsigned long *node, unsigned long opaque, 673 void (*func)(void *elem, unsigned long opaque, 674 unsigned long *key, size_t index, 675 void *func2), 676 void *func2, int reap, int height, size_t count) 677{ 678 int i; 679 unsigned long *child; 680 681 for (i = 0; i < geo->no_pairs; i++) { 682 child = bval(geo, node, i); 683 if (!child) 684 break; 685 if (height > 1) 686 count = __btree_for_each(head, geo, child, opaque, 687 func, func2, reap, height - 1, count); 688 else 689 func(child, opaque, bkey(geo, node, i), count++, 690 func2); 691 } 692 if (reap) 693 mempool_free(node, head->mempool); 694 return count; 695} 696 697static void empty(void *elem, unsigned long opaque, unsigned long *key, 698 size_t index, void *func2) 699{ 700} 701 702void visitorl(void *elem, unsigned long opaque, unsigned long *key, 703 size_t index, void *__func) 704{ 705 visitorl_t func = __func; 706 707 func(elem, opaque, *key, index); 708} 709EXPORT_SYMBOL_GPL(visitorl); 710 711void visitor32(void *elem, unsigned long opaque, unsigned long *__key, 712 size_t index, void *__func) 713{ 714 visitor32_t func = __func; 715 u32 *key = (void *)__key; 716 717 func(elem, opaque, *key, index); 718} 719EXPORT_SYMBOL_GPL(visitor32); 720 721void visitor64(void *elem, unsigned long opaque, unsigned long *__key, 722 size_t index, void *__func) 723{ 724 visitor64_t func = __func; 725 u64 *key = (void *)__key; 726 727 func(elem, opaque, *key, index); 728} 729EXPORT_SYMBOL_GPL(visitor64); 730 731void visitor128(void *elem, unsigned long opaque, unsigned long *__key, 732 size_t index, void *__func) 733{ 734 visitor128_t func = __func; 735 u64 *key = (void *)__key; 736 737 func(elem, opaque, key[0], key[1], index); 738} 739EXPORT_SYMBOL_GPL(visitor128); 740 741size_t btree_visitor(struct btree_head *head, struct btree_geo *geo, 742 unsigned long opaque, 743 void (*func)(void *elem, unsigned long opaque, 744 unsigned long *key, 745 size_t index, void *func2), 746 void *func2) 747{ 748 size_t count = 0; 749 750 if (!func2) 751 func = empty; 752 if (head->node) 753 count = __btree_for_each(head, geo, head->node, opaque, func, 754 func2, 0, head->height, 0); 755 return count; 756} 757EXPORT_SYMBOL_GPL(btree_visitor); 758 759size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo, 760 unsigned long opaque, 761 void (*func)(void *elem, unsigned long opaque, 762 unsigned long *key, 763 size_t index, void *func2), 764 void *func2) 765{ 766 size_t count = 0; 767 768 if (!func2) 769 func = empty; 770 if (head->node) 771 count = __btree_for_each(head, geo, head->node, opaque, func, 772 func2, 1, head->height, 0); 773 __btree_init(head); 774 return count; 775} 776EXPORT_SYMBOL_GPL(btree_grim_visitor); 777 778static int __init btree_module_init(void) 779{ 780 btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0, 781 SLAB_HWCACHE_ALIGN, NULL); 782 return 0; 783} 784 785static void __exit btree_module_exit(void) 786{ 787 kmem_cache_destroy(btree_cachep); 788} 789 790/* If core code starts using btree, initialization should happen even earlier */ 791module_init(btree_module_init); 792module_exit(btree_module_exit); 793 794MODULE_AUTHOR("Joern Engel <joern@logfs.org>"); 795MODULE_AUTHOR("Johannes Berg <johannes@sipsolutions.net>"); 796MODULE_LICENSE("GPL"); 797