net/ceph/crush/mapper.c

   1
   2 #ifdef __KERNEL__
   3 # include <linux/string.h>
   4 # include <linux/slab.h>
   5 # include <linux/bug.h>
   6 # include <linux/kernel.h>
   7 # ifndef dprintk
   8 #  define dprintk(args...)
   9 # endif
  10 #else
  11 # include <string.h>
  12 # include <stdio.h>
  13 # include <stdlib.h>
  14 # include <assert.h>
  15 # define BUG_ON(x) assert(!(x))
  16 # define dprintk(args...) /* printf(args) */
  17 # define kmalloc(x, f) malloc(x)
  18 # define kfree(x) free(x)
  19 #endif
  20
  21 #include <linux/crush/crush.h>
  22 #include <linux/crush/hash.h>
  23 #include <linux/crush/mapper.h>
  24
  25 /*
  26  * Implement the core CRUSH mapping algorithm.
  27  */
  28
  29 /**
  30  * crush_find_rule - find a crush_rule id for a given ruleset, type, and size.
  31  * @map: the crush_map
  32  * @ruleset: the storage ruleset id (user defined)
  33  * @type: storage ruleset type (user defined)
  34  * @size: output set size
  35  */
  36 int crush_find_rule(const struct crush_map *map, int ruleset, int type, int size)
  37 {
  38         __u32 i;
  39
  40         for (i = 0; i < map->max_rules; i++) {
  41                 if (map->rules[i] &&
  42                     map->rules[i]->mask.ruleset == ruleset &&
  43                     map->rules[i]->mask.type == type &&
  44                     map->rules[i]->mask.min_size <= size &&
  45                     map->rules[i]->mask.max_size >= size)
  46                         return i;
  47         }
  48         return -1;
  49 }
  50
  51
  52 /*
  53  * bucket choose methods
  54  *
  55  * For each bucket algorithm, we have a "choose" method that, given a
  56  * crush input @x and replica position (usually, position in output set) @r,
  57  * will produce an item in the bucket.
  58  */
  59
  60 /*
  61  * Choose based on a random permutation of the bucket.
  62  *
  63  * We used to use some prime number arithmetic to do this, but it
  64  * wasn't very random, and had some other bad behaviors.  Instead, we
  65  * calculate an actual random permutation of the bucket members.
  66  * Since this is expensive, we optimize for the r=0 case, which
  67  * captures the vast majority of calls.
  68  */
  69 static int bucket_perm_choose(struct crush_bucket *bucket,
  70                               int x, int r)
  71 {
  72         unsigned int pr = r % bucket->size;
  73         unsigned int i, s;
  74
  75         /* start a new permutation if @x has changed */
  76         if (bucket->perm_x != (__u32)x || bucket->perm_n == 0) {
  77                 dprintk("bucket %d new x=%d\n", bucket->id, x);
  78                 bucket->perm_x = x;
  79
  80                 /* optimize common r=0 case */
  81                 if (pr == 0) {
  82                         s = crush_hash32_3(bucket->hash, x, bucket->id, 0) %
  83                                 bucket->size;
  84                         bucket->perm[0] = s;
  85                         bucket->perm_n = 0xffff;   /* magic value, see below */
  86                         goto out;
  87                 }
  88
  89                 for (i = 0; i < bucket->size; i++)
  90                         bucket->perm[i] = i;
  91                 bucket->perm_n = 0;
  92         } else if (bucket->perm_n == 0xffff) {
  93                 /* clean up after the r=0 case above */
  94                 for (i = 1; i < bucket->size; i++)
  95                         bucket->perm[i] = i;
  96                 bucket->perm[bucket->perm[0]] = 0;
  97                 bucket->perm_n = 1;
  98         }
  99
 100         /* calculate permutation up to pr */
 101         for (i = 0; i < bucket->perm_n; i++)
 102                 dprintk(" perm_choose have %d: %d\n", i, bucket->perm[i]);
 103         while (bucket->perm_n <= pr) {
 104                 unsigned int p = bucket->perm_n;
 105                 /* no point in swapping the final entry */
 106                 if (p < bucket->size - 1) {
 107                         i = crush_hash32_3(bucket->hash, x, bucket->id, p) %
 108                                 (bucket->size - p);
 109                         if (i) {
 110                                 unsigned int t = bucket->perm[p + i];
 111                                 bucket->perm[p + i] = bucket->perm[p];
 112                                 bucket->perm[p] = t;
 113                         }
 114                         dprintk(" perm_choose swap %d with %d\n", p, p+i);
 115                 }
 116                 bucket->perm_n++;
 117         }
 118         for (i = 0; i < bucket->size; i++)
 119                 dprintk(" perm_choose  %d: %d\n", i, bucket->perm[i]);
 120
 121         s = bucket->perm[pr];
 122 out:
 123         dprintk(" perm_choose %d sz=%d x=%d r=%d (%d) s=%d\n", bucket->id,
 124                 bucket->size, x, r, pr, s);
 125         return bucket->items[s];
 126 }
 127
 128 /* uniform */
 129 static int bucket_uniform_choose(struct crush_bucket_uniform *bucket,
 130                                  int x, int r)
 131 {
 132         return bucket_perm_choose(&bucket->h, x, r);
 133 }
 134
 135 /* list */
 136 static int bucket_list_choose(struct crush_bucket_list *bucket,
 137                               int x, int r)
 138 {
 139         int i;
 140
 141         for (i = bucket->h.size-1; i >= 0; i--) {
 142                 __u64 w = crush_hash32_4(bucket->h.hash,x, bucket->h.items[i],
 143                                          r, bucket->h.id);
 144                 w &= 0xffff;
 145                 dprintk("list_choose i=%d x=%d r=%d item %d weight %x "
 146                         "sw %x rand %llx",
 147                         i, x, r, bucket->h.items[i], bucket->item_weights[i],
 148                         bucket->sum_weights[i], w);
 149                 w *= bucket->sum_weights[i];
 150                 w = w >> 16;
 151                 /*dprintk(" scaled %llx\n", w);*/
 152                 if (w < bucket->item_weights[i])
 153                         return bucket->h.items[i];
 154         }
 155
 156         dprintk("bad list sums for bucket %d\n", bucket->h.id);
 157         return bucket->h.items[0];
 158 }
 159
 160
 161 /* (binary) tree */
 162 static int height(int n)
 163 {
 164         int h = 0;
 165         while ((n & 1) == 0) {
 166                 h++;
 167                 n = n >> 1;
 168         }
 169         return h;
 170 }
 171
 172 static int left(int x)
 173 {
 174         int h = height(x);
 175         return x - (1 << (h-1));
 176 }
 177
 178 static int right(int x)
 179 {
 180         int h = height(x);
 181         return x + (1 << (h-1));
 182 }
 183
 184 static int terminal(int x)
 185 {
 186         return x & 1;
 187 }
 188
 189 static int bucket_tree_choose(struct crush_bucket_tree *bucket,
 190                               int x, int r)
 191 {
 192         int n;
 193         __u32 w;
 194         __u64 t;
 195
 196         /* start at root */
 197         n = bucket->num_nodes >> 1;
 198
 199         while (!terminal(n)) {
 200                 int l;
 201                 /* pick point in [0, w) */
 202                 w = bucket->node_weights[n];
 203                 t = (__u64)crush_hash32_4(bucket->h.hash, x, n, r,
 204                                           bucket->h.id) * (__u64)w;
 205                 t = t >> 32;
 206
 207                 /* descend to the left or right? */
 208                 l = left(n);
 209                 if (t < bucket->node_weights[l])
 210                         n = l;
 211                 else
 212                         n = right(n);
 213         }
 214
 215         return bucket->h.items[n >> 1];
 216 }
 217
 218
 219 /* straw */
 220
 221 static int bucket_straw_choose(struct crush_bucket_straw *bucket,
 222                                int x, int r)
 223 {
 224         __u32 i;
 225         int high = 0;
 226         __u64 high_draw = 0;
 227         __u64 draw;
 228
 229         for (i = 0; i < bucket->h.size; i++) {
 230                 draw = crush_hash32_3(bucket->h.hash, x, bucket->h.items[i], r);
 231                 draw &= 0xffff;
 232                 draw *= bucket->straws[i];
 233                 if (i == 0 || draw > high_draw) {
 234                         high = i;
 235                         high_draw = draw;
 236                 }
 237         }
 238         return bucket->h.items[high];
 239 }
 240
 241 static int crush_bucket_choose(struct crush_bucket *in, int x, int r)
 242 {
 243         dprintk(" crush_bucket_choose %d x=%d r=%d\n", in->id, x, r);
 244         BUG_ON(in->size == 0);
 245         switch (in->alg) {
 246         case CRUSH_BUCKET_UNIFORM:
 247                 return bucket_uniform_choose((struct crush_bucket_uniform *)in,
 248                                           x, r);
 249         case CRUSH_BUCKET_LIST:
 250                 return bucket_list_choose((struct crush_bucket_list *)in,
 251                                           x, r);
 252         case CRUSH_BUCKET_TREE:
 253                 return bucket_tree_choose((struct crush_bucket_tree *)in,
 254                                           x, r);
 255         case CRUSH_BUCKET_STRAW:
 256                 return bucket_straw_choose((struct crush_bucket_straw *)in,
 257                                            x, r);
 258         default:
 259                 dprintk("unknown bucket %d alg %d\n", in->id, in->alg);
 260                 return in->items[0];
 261         }
 262 }
 263
 264 /*
 265  * true if device is marked "out" (failed, fully offloaded)
 266  * of the cluster
 267  */
 268 static int is_out(const struct crush_map *map,
 269                   const __u32 *weight, int weight_max,
 270                   int item, int x)
 271 {
 272         if (item >= weight_max)
 273                 return 1;
 274         if (weight[item] >= 0x10000)
 275                 return 0;
 276         if (weight[item] == 0)
 277                 return 1;
 278         if ((crush_hash32_2(CRUSH_HASH_RJENKINS1, x, item) & 0xffff)
 279             < weight[item])
 280                 return 0;
 281         return 1;
 282 }
 283
 284 /**
 285  * crush_choose_firstn - choose numrep distinct items of given type
 286  * @map: the crush_map
 287  * @bucket: the bucket we are choose an item from
 288  * @x: crush input value
 289  * @numrep: the number of items to choose
 290  * @type: the type of item to choose
 291  * @out: pointer to output vector
 292  * @outpos: our position in that vector
 293  * @tries: number of attempts to make
 294  * @recurse_tries: number of attempts to have recursive chooseleaf make
 295  * @local_tries: localized retries
 296  * @local_fallback_tries: localized fallback retries
 297  * @recurse_to_leaf: true if we want one device under each item of given type (chooseleaf instead of choose)
 298  * @out2: second output vector for leaf items (if @recurse_to_leaf)
 299  */
 300 static int crush_choose_firstn(const struct crush_map *map,
 301                                struct crush_bucket *bucket,
 302                                const __u32 *weight, int weight_max,
 303                                int x, int numrep, int type,
 304                                int *out, int outpos,
 305                                unsigned int tries,
 306                                unsigned int recurse_tries,
 307                                unsigned int local_tries,
 308                                unsigned int local_fallback_tries,
 309                                int recurse_to_leaf,
 310                                int *out2)
 311 {
 312         int rep;
 313         unsigned int ftotal, flocal;
 314         int retry_descent, retry_bucket, skip_rep;
 315         struct crush_bucket *in = bucket;
 316         int r;
 317         int i;
 318         int item = 0;
 319         int itemtype;
 320         int collide, reject;
 321
 322         dprintk("CHOOSE%s bucket %d x %d outpos %d numrep %d\n", recurse_to_leaf ? "_LEAF" : "",
 323                 bucket->id, x, outpos, numrep);
 324
 325         for (rep = outpos; rep < numrep; rep++) {
 326                 /* keep trying until we get a non-out, non-colliding item */
 327                 ftotal = 0;
 328                 skip_rep = 0;
 329                 do {
 330                         retry_descent = 0;
 331                         in = bucket;               /* initial bucket */
 332
 333                         /* choose through intervening buckets */
 334                         flocal = 0;
 335                         do {
 336                                 collide = 0;
 337                                 retry_bucket = 0;
 338                                 r = rep;
 339                                 /* r' = r + f_total */
 340                                 r += ftotal;
 341
 342                                 /* bucket choose */
 343                                 if (in->size == 0) {
 344                                         reject = 1;
 345                                         goto reject;
 346                                 }
 347                                 if (local_fallback_tries > 0 &&
 348                                     flocal >= (in->size>>1) &&
 349                                     flocal > local_fallback_tries)
 350                                         item = bucket_perm_choose(in, x, r);
 351                                 else
 352                                         item = crush_bucket_choose(in, x, r);
 353                                 if (item >= map->max_devices) {
 354                                         dprintk("   bad item %d\n", item);
 355                                         skip_rep = 1;
 356                                         break;
 357                                 }
 358
 359                                 /* desired type? */
 360                                 if (item < 0)
 361                                         itemtype = map->buckets[-1-item]->type;
 362                                 else
 363                                         itemtype = 0;
 364                                 dprintk("  item %d type %d\n", item, itemtype);
 365
 366                                 /* keep going? */
 367                                 if (itemtype != type) {
 368                                         if (item >= 0 ||
 369                                             (-1-item) >= map->max_buckets) {
 370                                                 dprintk("   bad item type %d\n", type);
 371                                                 skip_rep = 1;
 372                                                 break;
 373                                         }
 374                                         in = map->buckets[-1-item];
 375                                         retry_bucket = 1;
 376                                         continue;
 377                                 }
 378
 379                                 /* collision? */
 380                                 for (i = 0; i < outpos; i++) {
 381                                         if (out[i] == item) {
 382                                                 collide = 1;
 383                                                 break;
 384                                         }
 385                                 }
 386
 387                                 reject = 0;
 388                                 if (!collide && recurse_to_leaf) {
 389                                         if (item < 0) {
 390                                                 if (crush_choose_firstn(map,
 391                                                          map->buckets[-1-item],
 392                                                          weight, weight_max,
 393                                                          x, outpos+1, 0,
 394                                                          out2, outpos,
 395                                                          recurse_tries, 0,
 396                                                          local_tries,
 397                                                          local_fallback_tries,
 398                                                          0,
 399                                                          NULL) <= outpos)
 400                                                         /* didn't get leaf */
 401                                                         reject = 1;
 402                                         } else {
 403                                                 /* we already have a leaf! */
 404                                                 out2[outpos] = item;
 405                                         }
 406                                 }
 407
 408                                 if (!reject) {
 409                                         /* out? */
 410                                         if (itemtype == 0)
 411                                                 reject = is_out(map, weight,
 412                                                                 weight_max,
 413                                                                 item, x);
 414                                         else
 415                                                 reject = 0;
 416                                 }
 417
 418 reject:
 419                                 if (reject || collide) {
 420                                         ftotal++;
 421                                         flocal++;
 422
 423                                         if (collide && flocal <= local_tries)
 424                                                 /* retry locally a few times */
 425                                                 retry_bucket = 1;
 426                                         else if (local_fallback_tries > 0 &&
 427                                                  flocal <= in->size + local_fallback_tries)
 428                                                 /* exhaustive bucket search */
 429                                                 retry_bucket = 1;
 430                                         else if (ftotal <= tries)
 431                                                 /* then retry descent */
 432                                                 retry_descent = 1;
 433                                         else
 434                                                 /* else give up */
 435                                                 skip_rep = 1;
 436                                         dprintk("  reject %d  collide %d  "
 437                                                 "ftotal %u  flocal %u\n",
 438                                                 reject, collide, ftotal,
 439                                                 flocal);
 440                                 }
 441                         } while (retry_bucket);
 442                 } while (retry_descent);
 443
 444                 if (skip_rep) {
 445                         dprintk("skip rep\n");
 446                         continue;
 447                 }
 448
 449                 dprintk("CHOOSE got %d\n", item);
 450                 out[outpos] = item;
 451                 outpos++;
 452         }
 453
 454         dprintk("CHOOSE returns %d\n", outpos);
 455         return outpos;
 456 }
 457
 458
 459 /**
 460  * crush_choose_indep: alternative breadth-first positionally stable mapping
 461  *
 462  */
 463 static void crush_choose_indep(const struct crush_map *map,
 464                                struct crush_bucket *bucket,
 465                                const __u32 *weight, int weight_max,
 466                                int x, int left, int numrep, int type,
 467                                int *out, int outpos,
 468                                unsigned int tries,
 469                                unsigned int recurse_tries,
 470                                int recurse_to_leaf,
 471                                int *out2,
 472                                int parent_r)
 473 {
 474         struct crush_bucket *in = bucket;
 475         int endpos = outpos + left;
 476         int rep;
 477         unsigned int ftotal;
 478         int r;
 479         int i;
 480         int item = 0;
 481         int itemtype;
 482         int collide;
 483
 484         dprintk("CHOOSE%s INDEP bucket %d x %d outpos %d numrep %d\n", recurse_to_leaf ? "_LEAF" : "",
 485                 bucket->id, x, outpos, numrep);
 486
 487         /* initially my result is undefined */
 488         for (rep = outpos; rep < endpos; rep++) {
 489                 out[rep] = CRUSH_ITEM_UNDEF;
 490                 if (out2)
 491                         out2[rep] = CRUSH_ITEM_UNDEF;
 492         }
 493
 494         for (ftotal = 0; left > 0 && ftotal < tries; ftotal++) {
 495                 for (rep = outpos; rep < endpos; rep++) {
 496                         if (out[rep] != CRUSH_ITEM_UNDEF)
 497                                 continue;
 498
 499                         in = bucket;  /* initial bucket */
 500
 501                         /* choose through intervening buckets */
 502                         for (;;) {
 503                                 /* note: we base the choice on the position
 504                                  * even in the nested call.  that means that
 505                                  * if the first layer chooses the same bucket
 506                                  * in a different position, we will tend to
 507                                  * choose a different item in that bucket.
 508                                  * this will involve more devices in data
 509                                  * movement and tend to distribute the load.
 510                                  */
 511                                 r = rep + parent_r;
 512
 513                                 /* be careful */
 514                                 if (in->alg == CRUSH_BUCKET_UNIFORM &&
 515                                     in->size % numrep == 0)
 516                                         /* r'=r+(n+1)*f_total */
 517                                         r += (numrep+1) * ftotal;
 518                                 else
 519                                         /* r' = r + n*f_total */
 520                                         r += numrep * ftotal;
 521
 522                                 /* bucket choose */
 523                                 if (in->size == 0) {
 524                                         dprintk("   empty bucket\n");
 525                                         break;
 526                                 }
 527
 528                                 item = crush_bucket_choose(in, x, r);
 529                                 if (item >= map->max_devices) {
 530                                         dprintk("   bad item %d\n", item);
 531                                         out[rep] = CRUSH_ITEM_NONE;
 532                                         if (out2)
 533                                                 out2[rep] = CRUSH_ITEM_NONE;
 534                                         left--;
 535                                         break;
 536                                 }
 537
 538                                 /* desired type? */
 539                                 if (item < 0)
 540                                         itemtype = map->buckets[-1-item]->type;
 541                                 else
 542                                         itemtype = 0;
 543                                 dprintk("  item %d type %d\n", item, itemtype);
 544
 545                                 /* keep going? */
 546                                 if (itemtype != type) {
 547                                         if (item >= 0 ||
 548                                             (-1-item) >= map->max_buckets) {
 549                                                 dprintk("   bad item type %d\n", type);
 550                                                 out[rep] = CRUSH_ITEM_NONE;
 551                                                 if (out2)
 552                                                         out2[rep] =
 553                                                                 CRUSH_ITEM_NONE;
 554                                                 left--;
 555                                                 break;
 556                                         }
 557                                         in = map->buckets[-1-item];
 558                                         continue;
 559                                 }
 560
 561                                 /* collision? */
 562                                 collide = 0;
 563                                 for (i = outpos; i < endpos; i++) {
 564                                         if (out[i] == item) {
 565                                                 collide = 1;
 566                                                 break;
 567                                         }
 568                                 }
 569                                 if (collide)
 570                                         break;
 571
 572                                 if (recurse_to_leaf) {
 573                                         if (item < 0) {
 574                                                 crush_choose_indep(map,
 575                                                    map->buckets[-1-item],
 576                                                    weight, weight_max,
 577                                                    x, 1, numrep, 0,
 578                                                    out2, rep,
 579                                                    recurse_tries, 0,
 580                                                    0, NULL, r);
 581                                                 if (out2[rep] == CRUSH_ITEM_NONE) {
 582                                                         /* placed nothing; no leaf */
 583                                                         break;
 584                                                 }
 585                                         } else {
 586                                                 /* we already have a leaf! */
 587                                                 out2[rep] = item;
 588                                         }
 589                                 }
 590
 591                                 /* out? */
 592                                 if (itemtype == 0 &&
 593                                     is_out(map, weight, weight_max, item, x))
 594                                         break;
 595
 596                                 /* yay! */
 597                                 out[rep] = item;
 598                                 left--;
 599                                 break;
 600                         }
 601                 }
 602         }
 603         for (rep = outpos; rep < endpos; rep++) {
 604                 if (out[rep] == CRUSH_ITEM_UNDEF) {
 605                         out[rep] = CRUSH_ITEM_NONE;
 606                 }
 607                 if (out2 && out2[rep] == CRUSH_ITEM_UNDEF) {
 608                         out2[rep] = CRUSH_ITEM_NONE;
 609                 }
 610         }
 611 }
 612
 613 /**
 614  * crush_do_rule - calculate a mapping with the given input and rule
 615  * @map: the crush_map
 616  * @ruleno: the rule id
 617  * @x: hash input
 618  * @result: pointer to result vector
 619  * @result_max: maximum result size
 620  * @weight: weight vector (for map leaves)
 621  * @weight_max: size of weight vector
 622  * @scratch: scratch vector for private use; must be >= 3 * result_max
 623  */
 624 int crush_do_rule(const struct crush_map *map,
 625                   int ruleno, int x, int *result, int result_max,
 626                   const __u32 *weight, int weight_max,
 627                   int *scratch)
 628 {
 629         int result_len;
 630         int *a = scratch;
 631         int *b = scratch + result_max;
 632         int *c = scratch + result_max*2;
 633         int recurse_to_leaf;
 634         int *w;
 635         int wsize = 0;
 636         int *o;
 637         int osize;
 638         int *tmp;
 639         struct crush_rule *rule;
 640         __u32 step;
 641         int i, j;
 642         int numrep;
 643         int choose_tries = map->choose_total_tries;
 644         int choose_local_tries = map->choose_local_tries;
 645         int choose_local_fallback_tries = map->choose_local_fallback_tries;
 646         int choose_leaf_tries = 0;
 647
 648         if ((__u32)ruleno >= map->max_rules) {
 649                 dprintk(" bad ruleno %d\n", ruleno);
 650                 return 0;
 651         }
 652
 653         rule = map->rules[ruleno];
 654         result_len = 0;
 655         w = a;
 656         o = b;
 657
 658         for (step = 0; step < rule->len; step++) {
 659                 int firstn = 0;
 660                 struct crush_rule_step *curstep = &rule->steps[step];
 661
 662                 switch (curstep->op) {
 663                 case CRUSH_RULE_TAKE:
 664                         w[0] = curstep->arg1;
 665                         wsize = 1;
 666                         break;
 667
 668                 case CRUSH_RULE_SET_CHOOSE_TRIES:
 669                         if (curstep->arg1 > 0)
 670                                 choose_tries = curstep->arg1;
 671                         break;
 672
 673                 case CRUSH_RULE_SET_CHOOSELEAF_TRIES:
 674                         if (curstep->arg1 > 0)
 675                                 choose_leaf_tries = curstep->arg1;
 676                         break;
 677
 678                 case CRUSH_RULE_SET_CHOOSE_LOCAL_TRIES:
 679                         if (curstep->arg1 > 0)
 680                                 choose_local_tries = curstep->arg1;
 681                         break;
 682
 683                 case CRUSH_RULE_SET_CHOOSE_LOCAL_FALLBACK_TRIES:
 684                         if (curstep->arg1 > 0)
 685                                 choose_local_fallback_tries = curstep->arg1;
 686                         break;
 687
 688                 case CRUSH_RULE_CHOOSELEAF_FIRSTN:
 689                 case CRUSH_RULE_CHOOSE_FIRSTN:
 690                         firstn = 1;
 691                         /* fall through */
 692                 case CRUSH_RULE_CHOOSELEAF_INDEP:
 693                 case CRUSH_RULE_CHOOSE_INDEP:
 694                         if (wsize == 0)
 695                                 break;
 696
 697                         recurse_to_leaf =
 698                                 curstep->op ==
 699                                  CRUSH_RULE_CHOOSELEAF_FIRSTN ||
 700                                 curstep->op ==
 701                                 CRUSH_RULE_CHOOSELEAF_INDEP;
 702
 703                         /* reset output */
 704                         osize = 0;
 705
 706                         for (i = 0; i < wsize; i++) {
 707                                 /*
 708                                  * see CRUSH_N, CRUSH_N_MINUS macros.
 709                                  * basically, numrep <= 0 means relative to
 710                                  * the provided result_max
 711                                  */
 712                                 numrep = curstep->arg1;
 713                                 if (numrep <= 0) {
 714                                         numrep += result_max;
 715                                         if (numrep <= 0)
 716                                                 continue;
 717                                 }
 718                                 j = 0;
 719                                 if (firstn) {
 720                                         int recurse_tries;
 721                                         if (choose_leaf_tries)
 722                                                 recurse_tries =
 723                                                         choose_leaf_tries;
 724                                         else if (map->chooseleaf_descend_once)
 725                                                 recurse_tries = 1;
 726                                         else
 727                                                 recurse_tries = choose_tries;
 728                                         osize += crush_choose_firstn(
 729                                                 map,
 730                                                 map->buckets[-1-w[i]],
 731                                                 weight, weight_max,
 732                                                 x, numrep,
 733                                                 curstep->arg2,
 734                                                 o+osize, j,
 735                                                 choose_tries,
 736                                                 recurse_tries,
 737                                                 choose_local_tries,
 738                                                 choose_local_fallback_tries,
 739                                                 recurse_to_leaf,
 740                                                 c+osize);
 741                                 } else {
 742                                         crush_choose_indep(
 743                                                 map,
 744                                                 map->buckets[-1-w[i]],
 745                                                 weight, weight_max,
 746                                                 x, numrep, numrep,
 747                                                 curstep->arg2,
 748                                                 o+osize, j,
 749                                                 choose_tries,
 750                                                 choose_leaf_tries ?
 751                                                    choose_leaf_tries : 1,
 752                                                 recurse_to_leaf,
 753                                                 c+osize,
 754                                                 0);
 755                                         osize += numrep;
 756                                 }
 757                         }
 758
 759                         if (recurse_to_leaf)
 760                                 /* copy final _leaf_ values to output set */
 761                                 memcpy(o, c, osize*sizeof(*o));
 762
 763                         /* swap o and w arrays */
 764                         tmp = o;
 765                         o = w;
 766                         w = tmp;
 767                         wsize = osize;
 768                         break;
 769
 770
 771                 case CRUSH_RULE_EMIT:
 772                         for (i = 0; i < wsize && result_len < result_max; i++) {
 773                                 result[result_len] = w[i];
 774                                 result_len++;
 775                         }
 776                         wsize = 0;
 777                         break;
 778
 779                 default:
 780                         dprintk(" unknown op %d at step %d\n",
 781                                 curstep->op, step);
 782                         break;
 783                 }
 784         }
 785         return result_len;
 786 }
 787
 788