sys/vfs/hammer2/hammer2_freemap.c

   1 /*
   2  * Copyright (c) 2011-2014 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Matthew Dillon <dillon@dragonflybsd.org>
   6  * by Venkatesh Srinivas <vsrinivas@dragonflybsd.org>
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  *
  12  * 1. Redistributions of source code must retain the above copyright
  13  *    notice, this list of conditions and the following disclaimer.
  14  * 2. Redistributions in binary form must reproduce the above copyright
  15  *    notice, this list of conditions and the following disclaimer in
  16  *    the documentation and/or other materials provided with the
  17  *    distribution.
  18  * 3. Neither the name of The DragonFly Project nor the names of its
  19  *    contributors may be used to endorse or promote products derived
  20  *    from this software without specific, prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  23  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  24  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  25  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  26  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  27  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  28  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  29  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  30  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  31  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  32  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  33  * SUCH DAMAGE.
  34  */
  35 #include <sys/param.h>
  36 #include <sys/systm.h>
  37 #include <sys/kernel.h>
  38 #include <sys/fcntl.h>
  39 #include <sys/buf.h>
  40 #include <sys/proc.h>
  41 #include <sys/namei.h>
  42 #include <sys/mount.h>
  43 #include <sys/vnode.h>
  44 #include <sys/mountctl.h>
  45
  46 #include "hammer2.h"
  47
  48 #define FREEMAP_DEBUG   0
  49
  50 struct hammer2_fiterate {
  51         hammer2_off_t   bpref;
  52         hammer2_off_t   bnext;
  53         int             loops;
  54 };
  55
  56 typedef struct hammer2_fiterate hammer2_fiterate_t;
  57
  58 static int hammer2_freemap_try_alloc(hammer2_chain_t **parentp,
  59                         hammer2_blockref_t *bref, int radix,
  60                         hammer2_fiterate_t *iter, hammer2_tid_t mtid);
  61 static void hammer2_freemap_init(hammer2_dev_t *hmp,
  62                         hammer2_key_t key, hammer2_chain_t *chain);
  63 static int hammer2_bmap_alloc(hammer2_dev_t *hmp,
  64                         hammer2_bmap_data_t *bmap, uint16_t class,
  65                         int n, int radix, hammer2_key_t *basep);
  66 static int hammer2_freemap_iterate(hammer2_chain_t **parentp,
  67                         hammer2_chain_t **chainp,
  68                         hammer2_fiterate_t *iter);
  69
  70 static __inline
  71 int
  72 hammer2_freemapradix(int radix)
  73 {
  74         return(radix);
  75 }
  76
  77 /*
  78  * Calculate the device offset for the specified FREEMAP_NODE or FREEMAP_LEAF
  79  * bref.  Return a combined media offset and physical size radix.  Freemap
  80  * chains use fixed storage offsets in the 4MB reserved area at the
  81  * beginning of each 2GB zone
  82  *
  83  * Rotate between four possibilities.  Theoretically this means we have three
  84  * good freemaps in case of a crash which we can use as a base for the fixup
  85  * scan at mount-time.
  86  */
  87 #define H2FMBASE(key, radix)    ((key) & ~(((hammer2_off_t)1 << (radix)) - 1))
  88 #define H2FMSHIFT(radix)        ((hammer2_off_t)1 << (radix))
  89
  90 static
  91 int
  92 hammer2_freemap_reserve(hammer2_chain_t *chain, int radix)
  93 {
  94         hammer2_blockref_t *bref = &chain->bref;
  95         hammer2_off_t off;
  96         int index;
  97         int index_inc;
  98         size_t bytes;
  99
 100         /*
 101          * Physical allocation size.
 102          */
 103         bytes = (size_t)1 << radix;
 104
 105         /*
 106          * Calculate block selection index 0..7 of current block.  If this
 107          * is the first allocation of the block (verses a modification of an
 108          * existing block), we use index 0, otherwise we use the next rotating
 109          * index.
 110          */
 111         if ((bref->data_off & ~HAMMER2_OFF_MASK_RADIX) == 0) {
 112                 index = 0;
 113         } else {
 114                 off = bref->data_off & ~HAMMER2_OFF_MASK_RADIX &
 115                       (((hammer2_off_t)1 <<
 116                         HAMMER2_FREEMAP_LEVEL1_RADIX) - 1);
 117                 off = off / HAMMER2_PBUFSIZE;
 118                 KKASSERT(off >= HAMMER2_ZONE_FREEMAP_00 &&
 119                          off < HAMMER2_ZONE_FREEMAP_END);
 120                 index = (int)(off - HAMMER2_ZONE_FREEMAP_00) /
 121                         HAMMER2_ZONE_FREEMAP_INC;
 122                 KKASSERT(index >= 0 && index < HAMMER2_NFREEMAPS);
 123                 if (++index == HAMMER2_NFREEMAPS)
 124                         index = 0;
 125         }
 126
 127         /*
 128          * Calculate the block offset of the reserved block.  This will
 129          * point into the 4MB reserved area at the base of the appropriate
 130          * 2GB zone, once added to the FREEMAP_x selection above.
 131          */
 132         index_inc = index * HAMMER2_ZONE_FREEMAP_INC;
 133
 134         switch(bref->keybits) {
 135         /* case HAMMER2_FREEMAP_LEVEL6_RADIX: not applicable */
 136         case HAMMER2_FREEMAP_LEVEL5_RADIX:      /* 2EB */
 137                 KKASSERT(bref->type == HAMMER2_BREF_TYPE_FREEMAP_NODE);
 138                 KKASSERT(bytes == HAMMER2_FREEMAP_LEVELN_PSIZE);
 139                 off = H2FMBASE(bref->key, HAMMER2_FREEMAP_LEVEL5_RADIX) +
 140                       (index_inc + HAMMER2_ZONE_FREEMAP_00 +
 141                        HAMMER2_ZONEFM_LEVEL5) * HAMMER2_PBUFSIZE;
 142                 break;
 143         case HAMMER2_FREEMAP_LEVEL4_RADIX:      /* 2EB */
 144                 KKASSERT(bref->type == HAMMER2_BREF_TYPE_FREEMAP_NODE);
 145                 KKASSERT(bytes == HAMMER2_FREEMAP_LEVELN_PSIZE);
 146                 off = H2FMBASE(bref->key, HAMMER2_FREEMAP_LEVEL4_RADIX) +
 147                       (index_inc + HAMMER2_ZONE_FREEMAP_00 +
 148                        HAMMER2_ZONEFM_LEVEL4) * HAMMER2_PBUFSIZE;
 149                 break;
 150         case HAMMER2_FREEMAP_LEVEL3_RADIX:      /* 2PB */
 151                 KKASSERT(bref->type == HAMMER2_BREF_TYPE_FREEMAP_NODE);
 152                 KKASSERT(bytes == HAMMER2_FREEMAP_LEVELN_PSIZE);
 153                 off = H2FMBASE(bref->key, HAMMER2_FREEMAP_LEVEL3_RADIX) +
 154                       (index_inc + HAMMER2_ZONE_FREEMAP_00 +
 155                        HAMMER2_ZONEFM_LEVEL3) * HAMMER2_PBUFSIZE;
 156                 break;
 157         case HAMMER2_FREEMAP_LEVEL2_RADIX:      /* 2TB */
 158                 KKASSERT(bref->type == HAMMER2_BREF_TYPE_FREEMAP_NODE);
 159                 KKASSERT(bytes == HAMMER2_FREEMAP_LEVELN_PSIZE);
 160                 off = H2FMBASE(bref->key, HAMMER2_FREEMAP_LEVEL2_RADIX) +
 161                       (index_inc + HAMMER2_ZONE_FREEMAP_00 +
 162                        HAMMER2_ZONEFM_LEVEL2) * HAMMER2_PBUFSIZE;
 163                 break;
 164         case HAMMER2_FREEMAP_LEVEL1_RADIX:      /* 2GB */
 165                 KKASSERT(bref->type == HAMMER2_BREF_TYPE_FREEMAP_LEAF);
 166                 KKASSERT(bytes == HAMMER2_FREEMAP_LEVELN_PSIZE);
 167                 off = H2FMBASE(bref->key, HAMMER2_FREEMAP_LEVEL1_RADIX) +
 168                       (index_inc + HAMMER2_ZONE_FREEMAP_00 +
 169                        HAMMER2_ZONEFM_LEVEL1) * HAMMER2_PBUFSIZE;
 170                 break;
 171         default:
 172                 panic("freemap: bad radix(2) %p %d\n", bref, bref->keybits);
 173                 /* NOT REACHED */
 174                 off = (hammer2_off_t)-1;
 175                 break;
 176         }
 177         bref->data_off = off | radix;
 178 #if FREEMAP_DEBUG
 179         kprintf("FREEMAP BLOCK TYPE %d %016jx/%d DATA_OFF=%016jx\n",
 180                 bref->type, bref->key, bref->keybits, bref->data_off);
 181 #endif
 182         return (0);
 183 }
 184
 185 /*
 186  * Normal freemap allocator
 187  *
 188  * Use available hints to allocate space using the freemap.  Create missing
 189  * freemap infrastructure on-the-fly as needed (including marking initial
 190  * allocations using the iterator as allocated, instantiating new 2GB zones,
 191  * and dealing with the end-of-media edge case).
 192  *
 193  * ip and bpref are only used as a heuristic to determine locality of
 194  * reference.  bref->key may also be used heuristically.
 195  */
 196 int
 197 hammer2_freemap_alloc(hammer2_chain_t *chain, size_t bytes)
 198 {
 199         hammer2_dev_t *hmp = chain->hmp;
 200         hammer2_blockref_t *bref = &chain->bref;
 201         hammer2_chain_t *parent;
 202         hammer2_tid_t mtid;
 203         int radix;
 204         int error;
 205         unsigned int hindex;
 206         hammer2_fiterate_t iter;
 207
 208         mtid = hammer2_trans_sub(hmp->spmp);
 209
 210         /*
 211          * Validate the allocation size.  It must be a power of 2.
 212          *
 213          * For now require that the caller be aware of the minimum
 214          * allocation (1K).
 215          */
 216         radix = hammer2_getradix(bytes);
 217         KKASSERT((size_t)1 << radix == bytes);
 218
 219         if (bref->type == HAMMER2_BREF_TYPE_FREEMAP_NODE ||
 220             bref->type == HAMMER2_BREF_TYPE_FREEMAP_LEAF) {
 221                 /*
 222                  * Freemap blocks themselves are assigned from the reserve
 223                  * area, not allocated from the freemap.
 224                  */
 225                 error = hammer2_freemap_reserve(chain, radix);
 226                 return error;
 227         }
 228
 229         KKASSERT(bytes >= HAMMER2_ALLOC_MIN && bytes <= HAMMER2_ALLOC_MAX);
 230
 231         /*
 232          * Calculate the starting point for our allocation search.
 233          *
 234          * Each freemap leaf is dedicated to a specific freemap_radix.
 235          * The freemap_radix can be more fine-grained than the device buffer
 236          * radix which results in inodes being grouped together in their
 237          * own segment, terminal-data (16K or less) and initial indirect
 238          * block being grouped together, and then full-indirect and full-data
 239          * blocks (64K) being grouped together.
 240          *
 241          * The single most important aspect of this is the inode grouping
 242          * because that is what allows 'find' and 'ls' and other filesystem
 243          * topology operations to run fast.
 244          */
 245 #if 0
 246         if (bref->data_off & ~HAMMER2_OFF_MASK_RADIX)
 247                 bpref = bref->data_off & ~HAMMER2_OFF_MASK_RADIX;
 248         else if (trans->tmp_bpref)
 249                 bpref = trans->tmp_bpref;
 250         else if (trans->tmp_ip)
 251                 bpref = trans->tmp_ip->chain->bref.data_off;
 252         else
 253 #endif
 254         /*
 255          * Heuristic tracking index.  We would like one for each distinct
 256          * bref type if possible.  heur_freemap[] has room for two classes
 257          * for each type.  At a minimum we have to break-up our heuristic
 258          * by device block sizes.
 259          */
 260         hindex = hammer2_devblkradix(radix) - HAMMER2_MINIORADIX;
 261         KKASSERT(hindex < HAMMER2_FREEMAP_HEUR_NRADIX);
 262         hindex += bref->type * HAMMER2_FREEMAP_HEUR_NRADIX;
 263         hindex &= HAMMER2_FREEMAP_HEUR_TYPES * HAMMER2_FREEMAP_HEUR_NRADIX - 1;
 264         KKASSERT(hindex < HAMMER2_FREEMAP_HEUR);
 265
 266         iter.bpref = hmp->heur_freemap[hindex];
 267
 268         /*
 269          * Make sure bpref is in-bounds.  It's ok if bpref covers a zone's
 270          * reserved area, the try code will iterate past it.
 271          */
 272         if (iter.bpref > hmp->voldata.volu_size)
 273                 iter.bpref = hmp->voldata.volu_size - 1;
 274
 275         /*
 276          * Iterate the freemap looking for free space before and after.
 277          */
 278         parent = &hmp->fchain;
 279         hammer2_chain_ref(parent);
 280         hammer2_chain_lock(parent, HAMMER2_RESOLVE_ALWAYS);
 281         error = EAGAIN;
 282         iter.bnext = iter.bpref;
 283         iter.loops = 0;
 284
 285         while (error == EAGAIN) {
 286                 error = hammer2_freemap_try_alloc(&parent, bref, radix,
 287                                                   &iter, mtid);
 288         }
 289         hmp->heur_freemap[hindex] = iter.bnext;
 290         hammer2_chain_unlock(parent);
 291         hammer2_chain_drop(parent);
 292
 293         return (error);
 294 }
 295
 296 static int
 297 hammer2_freemap_try_alloc(hammer2_chain_t **parentp,
 298                           hammer2_blockref_t *bref, int radix,
 299                           hammer2_fiterate_t *iter, hammer2_tid_t mtid)
 300 {
 301         hammer2_dev_t *hmp = (*parentp)->hmp;
 302         hammer2_off_t l0size;
 303         hammer2_off_t l1size;
 304         hammer2_off_t l1mask;
 305         hammer2_key_t key_dummy;
 306         hammer2_chain_t *chain;
 307         hammer2_off_t key;
 308         size_t bytes;
 309         uint16_t class;
 310         int error = 0;
 311         int cache_index = -1;
 312
 313         /*
 314          * Calculate the number of bytes being allocated, the number
 315          * of contiguous bits of bitmap being allocated, and the bitmap
 316          * mask.
 317          *
 318          * WARNING! cpu hardware may mask bits == 64 -> 0 and blow up the
 319          *          mask calculation.
 320          */
 321         bytes = (size_t)1 << radix;
 322         class = (bref->type << 8) | hammer2_devblkradix(radix);
 323
 324         /*
 325          * Lookup the level1 freemap chain, creating and initializing one
 326          * if necessary.  Intermediate levels will be created automatically
 327          * when necessary by hammer2_chain_create().
 328          */
 329         key = H2FMBASE(iter->bnext, HAMMER2_FREEMAP_LEVEL1_RADIX);
 330         l0size = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL0_RADIX);
 331         l1size = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
 332         l1mask = l1size - 1;
 333
 334         chain = hammer2_chain_lookup(parentp, &key_dummy, key, key + l1mask,
 335                                      &cache_index,
 336                                      HAMMER2_LOOKUP_ALWAYS |
 337                                      HAMMER2_LOOKUP_MATCHIND);
 338
 339         if (chain == NULL) {
 340                 /*
 341                  * Create the missing leaf, be sure to initialize
 342                  * the auxillary freemap tracking information in
 343                  * the bref.check.freemap structure.
 344                  */
 345 #if 0
 346                 kprintf("freemap create L1 @ %016jx bpref %016jx\n",
 347                         key, iter->bpref);
 348 #endif
 349                 error = hammer2_chain_create(parentp, &chain, hmp->spmp,
 350                                      key, HAMMER2_FREEMAP_LEVEL1_RADIX,
 351                                      HAMMER2_BREF_TYPE_FREEMAP_LEAF,
 352                                      HAMMER2_FREEMAP_LEVELN_PSIZE,
 353                                      mtid, 0);
 354                 KKASSERT(error == 0);
 355                 if (error == 0) {
 356                         hammer2_chain_modify(chain, mtid, 0);
 357                         bzero(&chain->data->bmdata[0],
 358                               HAMMER2_FREEMAP_LEVELN_PSIZE);
 359                         chain->bref.check.freemap.bigmask = (uint32_t)-1;
 360                         chain->bref.check.freemap.avail = l1size;
 361                         /* bref.methods should already be inherited */
 362
 363                         hammer2_freemap_init(hmp, key, chain);
 364                 }
 365         } else if (chain->error) {
 366                 /*
 367                  * Error during lookup.
 368                  */
 369                 kprintf("hammer2_freemap_try_alloc: %016jx: error %s\n",
 370                         (intmax_t)bref->data_off,
 371                         hammer2_error_str(chain->error));
 372                 error = EIO;
 373         } else if ((chain->bref.check.freemap.bigmask &
 374                    ((size_t)1 << radix)) == 0) {
 375                 /*
 376                  * Already flagged as not having enough space
 377                  */
 378                 error = ENOSPC;
 379         } else {
 380                 /*
 381                  * Modify existing chain to setup for adjustment.
 382                  */
 383                 hammer2_chain_modify(chain, mtid, 0);
 384         }
 385
 386         /*
 387          * Scan 2MB entries.
 388          */
 389         if (error == 0) {
 390                 hammer2_bmap_data_t *bmap;
 391                 hammer2_key_t base_key;
 392                 int count;
 393                 int start;
 394                 int n;
 395
 396                 KKASSERT(chain->bref.type == HAMMER2_BREF_TYPE_FREEMAP_LEAF);
 397                 start = (int)((iter->bnext - key) >>
 398                               HAMMER2_FREEMAP_LEVEL0_RADIX);
 399                 KKASSERT(start >= 0 && start < HAMMER2_FREEMAP_COUNT);
 400                 hammer2_chain_modify(chain, mtid, 0);
 401
 402                 error = ENOSPC;
 403                 for (count = 0; count < HAMMER2_FREEMAP_COUNT; ++count) {
 404                         int availchk;
 405
 406                         if (start + count >= HAMMER2_FREEMAP_COUNT &&
 407                             start - count < 0) {
 408                                 break;
 409                         }
 410
 411                         /*
 412                          * Calculate bmap pointer
 413                          *
 414                          * NOTE: bmap pointer is invalid if n >= FREEMAP_COUNT.
 415                          */
 416                         n = start + count;
 417                         bmap = &chain->data->bmdata[n];
 418
 419                         if (n >= HAMMER2_FREEMAP_COUNT) {
 420                                 availchk = 0;
 421                         } else if (bmap->avail) {
 422                                 availchk = 1;
 423                         } else if (radix < HAMMER2_FREEMAP_BLOCK_RADIX &&
 424                                   (bmap->linear & HAMMER2_FREEMAP_BLOCK_MASK)) {
 425                                 availchk = 1;
 426                         } else {
 427                                 availchk = 0;
 428                         }
 429
 430                         if (availchk &&
 431                             (bmap->class == 0 || bmap->class == class)) {
 432                                 base_key = key + n * l0size;
 433                                 error = hammer2_bmap_alloc(hmp, bmap,
 434                                                            class, n, radix,
 435                                                            &base_key);
 436                                 if (error != ENOSPC) {
 437                                         key = base_key;
 438                                         break;
 439                                 }
 440                         }
 441
 442                         /*
 443                          * Must recalculate after potentially having called
 444                          * hammer2_bmap_alloc() above in case chain was
 445                          * reallocated.
 446                          *
 447                          * NOTE: bmap pointer is invalid if n < 0.
 448                          */
 449                         n = start - count;
 450                         bmap = &chain->data->bmdata[n];
 451                         if (n < 0) {
 452                                 availchk = 0;
 453                         } else if (bmap->avail) {
 454                                 availchk = 1;
 455                         } else if (radix < HAMMER2_FREEMAP_BLOCK_RADIX &&
 456                                   (bmap->linear & HAMMER2_FREEMAP_BLOCK_MASK)) {
 457                                 availchk = 1;
 458                         } else {
 459                                 availchk = 0;
 460                         }
 461
 462                         if (availchk &&
 463                             (bmap->class == 0 || bmap->class == class)) {
 464                                 base_key = key + n * l0size;
 465                                 error = hammer2_bmap_alloc(hmp, bmap,
 466                                                            class, n, radix,
 467                                                            &base_key);
 468                                 if (error != ENOSPC) {
 469                                         key = base_key;
 470                                         break;
 471                                 }
 472                         }
 473                 }
 474                 if (error == ENOSPC) {
 475                         chain->bref.check.freemap.bigmask &=
 476                                 (uint32_t)~((size_t)1 << radix);
 477                 }
 478                 /* XXX also scan down from original count */
 479         }
 480
 481         if (error == 0) {
 482                 /*
 483                  * Assert validity.  Must be beyond the static allocator used
 484                  * by newfs_hammer2 (and thus also beyond the aux area),
 485                  * not go past the volume size, and must not be in the
 486                  * reserved segment area for a zone.
 487                  */
 488                 KKASSERT(key >= hmp->voldata.allocator_beg &&
 489                          key + bytes <= hmp->voldata.volu_size);
 490                 KKASSERT((key & HAMMER2_ZONE_MASK64) >= HAMMER2_ZONE_SEG);
 491                 bref->data_off = key | radix;
 492
 493 #if 0
 494                 kprintf("alloc cp=%p %016jx %016jx using %016jx\n",
 495                         chain,
 496                         bref->key, bref->data_off, chain->bref.data_off);
 497 #endif
 498         } else if (error == ENOSPC) {
 499                 /*
 500                  * Return EAGAIN with next iteration in iter->bnext, or
 501                  * return ENOSPC if the allocation map has been exhausted.
 502                  */
 503                 error = hammer2_freemap_iterate(parentp, &chain, iter);
 504         }
 505
 506         /*
 507          * Cleanup
 508          */
 509         if (chain) {
 510                 hammer2_chain_unlock(chain);
 511                 hammer2_chain_drop(chain);
 512         }
 513         return (error);
 514 }
 515
 516 /*
 517  * Allocate (1<<radix) bytes from the bmap whos base data offset is (*basep).
 518  *
 519  * If the linear iterator is mid-block we use it directly (the bitmap should
 520  * already be marked allocated), otherwise we search for a block in the bitmap
 521  * that fits the allocation request.
 522  *
 523  * A partial bitmap allocation sets the minimum bitmap granularity (16KB)
 524  * to fully allocated and adjusts the linear allocator to allow the
 525  * remaining space to be allocated.
 526  */
 527 static
 528 int
 529 hammer2_bmap_alloc(hammer2_dev_t *hmp, hammer2_bmap_data_t *bmap,
 530                    uint16_t class, int n, int radix, hammer2_key_t *basep)
 531 {
 532         hammer2_io_t *dio;
 533         size_t size;
 534         size_t bgsize;
 535         int bmradix;
 536         hammer2_bitmap_t bmmask;
 537         int offset;
 538         int error;
 539         int i;
 540         int j;
 541
 542         /*
 543          * Take into account 2-bits per block when calculating bmradix.
 544          */
 545         size = (size_t)1 << radix;
 546
 547         if (radix <= HAMMER2_FREEMAP_BLOCK_RADIX) {
 548                 bmradix = 2;
 549                 /* (16K) 2 bits per allocation block */
 550         } else {
 551                 bmradix = (hammer2_bitmap_t)2 <<
 552                           (radix - HAMMER2_FREEMAP_BLOCK_RADIX);
 553                 /* (32K-256K) 4, 8, 16, 32 bits per allocation block */
 554         }
 555
 556         /*
 557          * Use the linear iterator to pack small allocations, otherwise
 558          * fall-back to finding a free 16KB chunk.  The linear iterator
 559          * is only valid when *NOT* on a freemap chunking boundary (16KB).
 560          * If it is the bitmap must be scanned.  It can become invalid
 561          * once we pack to the boundary.  We adjust it after a bitmap
 562          * allocation only for sub-16KB allocations (so the perfectly good
 563          * previous value can still be used for fragments when 16KB+
 564          * allocations are made).
 565          *
 566          * Beware of hardware artifacts when bmradix == 64 (intermediate
 567          * result can wind up being '1' instead of '0' if hardware masks
 568          * bit-count & 31).
 569          *
 570          * NOTE: j needs to be even in the j= calculation.  As an artifact
 571          *       of the /2 division, our bitmask has to clear bit 0.
 572          *
 573          * NOTE: TODO this can leave little unallocatable fragments lying
 574          *       around.
 575          */
 576         if (((uint32_t)bmap->linear & HAMMER2_FREEMAP_BLOCK_MASK) + size <=
 577             HAMMER2_FREEMAP_BLOCK_SIZE &&
 578             (bmap->linear & HAMMER2_FREEMAP_BLOCK_MASK) &&
 579             bmap->linear < HAMMER2_SEGSIZE) {
 580                 KKASSERT(bmap->linear >= 0 &&
 581                          bmap->linear + size <= HAMMER2_SEGSIZE &&
 582                          (bmap->linear & (HAMMER2_ALLOC_MIN - 1)) == 0);
 583                 offset = bmap->linear;
 584                 i = offset / (HAMMER2_SEGSIZE / 8);
 585                 j = (offset / (HAMMER2_FREEMAP_BLOCK_SIZE / 2)) & 30;
 586                 bmmask = (bmradix == HAMMER2_BMAP_BITS_PER_ELEMENT) ?
 587                          HAMMER2_BMAP_ALLONES :
 588                          ((hammer2_bitmap_t)1 << bmradix) - 1;
 589                 bmmask <<= j;
 590                 bmap->linear = offset + size;
 591         } else {
 592                 for (i = 0; i < HAMMER2_BMAP_ELEMENTS; ++i) {
 593                         bmmask = (bmradix == HAMMER2_BMAP_BITS_PER_ELEMENT) ?
 594                                  HAMMER2_BMAP_ALLONES :
 595                                  ((hammer2_bitmap_t)1 << bmradix) - 1;
 596                         for (j = 0;
 597                              j < HAMMER2_BMAP_BITS_PER_ELEMENT;
 598                              j += bmradix) {
 599                                 if ((bmap->bitmapq[i] & bmmask) == 0)
 600                                         goto success;
 601                                 bmmask <<= bmradix;
 602                         }
 603                 }
 604                 /*fragments might remain*/
 605                 /*KKASSERT(bmap->avail == 0);*/
 606                 return (ENOSPC);
 607 success:
 608                 offset = i * (HAMMER2_SEGSIZE / HAMMER2_BMAP_ELEMENTS) +
 609                          (j * (HAMMER2_FREEMAP_BLOCK_SIZE / 2));
 610                 if (size & HAMMER2_FREEMAP_BLOCK_MASK)
 611                         bmap->linear = offset + size;
 612         }
 613
 614         /* 8 x (64/2) -> 256 x 16K -> 4MB */
 615         KKASSERT(i >= 0 && i < HAMMER2_BMAP_ELEMENTS);
 616
 617         /*
 618          * Optimize the buffer cache to avoid unnecessary read-before-write
 619          * operations.
 620          *
 621          * The device block size could be larger than the allocation size
 622          * so the actual bitmap test is somewhat more involved.  We have
 623          * to use a compatible buffer size for this operation.
 624          */
 625         if ((bmap->bitmapq[i] & bmmask) == 0 &&
 626             hammer2_devblksize(size) != size) {
 627                 size_t psize = hammer2_devblksize(size);
 628                 hammer2_off_t pmask = (hammer2_off_t)psize - 1;
 629                 int pbmradix = (hammer2_bitmap_t)2 <<
 630                                         (hammer2_devblkradix(radix) -
 631                                HAMMER2_FREEMAP_BLOCK_RADIX);
 632                 hammer2_bitmap_t pbmmask;
 633                 int pradix = hammer2_getradix(psize);
 634
 635                 pbmmask = (pbmradix == HAMMER2_BMAP_BITS_PER_ELEMENT) ?
 636                         HAMMER2_BMAP_ALLONES :
 637                         ((hammer2_bitmap_t)1 << pbmradix) - 1;
 638                 while ((pbmmask & bmmask) == 0)
 639                         pbmmask <<= pbmradix;
 640
 641 #if 0
 642                 kprintf("%016jx mask %016jx %016jx %016jx (%zd/%zd)\n",
 643                         *basep + offset, bmap->bitmapq[i],
 644                         pbmmask, bmmask, size, psize);
 645 #endif
 646
 647                 if ((bmap->bitmapq[i] & pbmmask) == 0) {
 648                         error = hammer2_io_newq(hmp,
 649                                                 (*basep + (offset & ~pmask)) |
 650                                                  pradix,
 651                                                 psize, &dio);
 652                         hammer2_io_bqrelse(&dio);
 653                 }
 654         }
 655
 656 #if 0
 657         /*
 658          * When initializing a new inode segment also attempt to initialize
 659          * an adjacent segment.  Be careful not to index beyond the array
 660          * bounds.
 661          *
 662          * We do this to try to localize inode accesses to improve
 663          * directory scan rates.  XXX doesn't improve scan rates.
 664          */
 665         if (size == HAMMER2_INODE_BYTES) {
 666                 if (n & 1) {
 667                         if (bmap[-1].radix == 0 && bmap[-1].avail)
 668                                 bmap[-1].radix = radix;
 669                 } else {
 670                         if (bmap[1].radix == 0 && bmap[1].avail)
 671                                 bmap[1].radix = radix;
 672                 }
 673         }
 674 #endif
 675         /*
 676          * Calculate the bitmap-granular change in bgsize for the volume
 677          * header.  We cannot use the fine-grained change here because
 678          * the bulkfree code can't undo it.  If the bitmap element is already
 679          * marked allocated it has already been accounted for.
 680          */
 681         if (radix < HAMMER2_FREEMAP_BLOCK_RADIX) {
 682                 if (bmap->bitmapq[i] & bmmask)
 683                         bgsize = 0;
 684                 else
 685                         bgsize = HAMMER2_FREEMAP_BLOCK_SIZE;
 686         } else {
 687                 bgsize = size;
 688         }
 689
 690         /*
 691          * Adjust the bitmap, set the class (it might have been 0),
 692          * and available bytes, update the allocation offset (*basep)
 693          * from the L0 base to the actual offset.
 694          *
 695          * avail must reflect the bitmap-granular availability.  The allocator
 696          * tests will also check the linear iterator.
 697          */
 698         bmap->bitmapq[i] |= bmmask;
 699         bmap->class = class;
 700         bmap->avail -= bgsize;
 701         *basep += offset;
 702
 703         /*
 704          * Adjust the volume header's allocator_free parameter.  This
 705          * parameter has to be fixed up by bulkfree which has no way to
 706          * figure out sub-16K chunking, so it must be adjusted by the
 707          * bitmap-granular size.
 708          */
 709         if (bgsize) {
 710                 hammer2_voldata_lock(hmp);
 711                 hammer2_voldata_modify(hmp);
 712                 hmp->voldata.allocator_free -= bgsize;
 713                 hammer2_voldata_unlock(hmp);
 714         }
 715
 716         return(0);
 717 }
 718
 719 static
 720 void
 721 hammer2_freemap_init(hammer2_dev_t *hmp, hammer2_key_t key,
 722                      hammer2_chain_t *chain)
 723 {
 724         hammer2_off_t l1size;
 725         hammer2_off_t lokey;
 726         hammer2_off_t hikey;
 727         hammer2_bmap_data_t *bmap;
 728         int count;
 729
 730         l1size = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
 731
 732         /*
 733          * Calculate the portion of the 2GB map that should be initialized
 734          * as free.  Portions below or after will be initialized as allocated.
 735          * SEGMASK-align the areas so we don't have to worry about sub-scans
 736          * or endianess when using memset.
 737          *
 738          * (1) Ensure that all statically allocated space from newfs_hammer2
 739          *     is marked allocated.
 740          *
 741          * (2) Ensure that the reserved area is marked allocated (typically
 742          *     the first 4MB of the 2GB area being represented).
 743          *
 744          * (3) Ensure that any trailing space at the end-of-volume is marked
 745          *     allocated.
 746          *
 747          * WARNING! It is possible for lokey to be larger than hikey if the
 748          *          entire 2GB segment is within the static allocation.
 749          */
 750         lokey = (hmp->voldata.allocator_beg + HAMMER2_SEGMASK64) &
 751                 ~HAMMER2_SEGMASK64;
 752
 753         if (lokey < H2FMBASE(key, HAMMER2_FREEMAP_LEVEL1_RADIX) +
 754                   HAMMER2_ZONE_SEG64) {
 755                 lokey = H2FMBASE(key, HAMMER2_FREEMAP_LEVEL1_RADIX) +
 756                         HAMMER2_ZONE_SEG64;
 757         }
 758
 759         hikey = key + H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
 760         if (hikey > hmp->voldata.volu_size) {
 761                 hikey = hmp->voldata.volu_size & ~HAMMER2_SEGMASK64;
 762         }
 763
 764         chain->bref.check.freemap.avail =
 765                 H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
 766         bmap = &chain->data->bmdata[0];
 767
 768         for (count = 0; count < HAMMER2_FREEMAP_COUNT; ++count) {
 769                 if (key < lokey || key >= hikey) {
 770                         memset(bmap->bitmapq, -1,
 771                                sizeof(bmap->bitmapq));
 772                         bmap->avail = 0;
 773                         bmap->linear = HAMMER2_SEGSIZE;
 774                         chain->bref.check.freemap.avail -=
 775                                 H2FMSHIFT(HAMMER2_FREEMAP_LEVEL0_RADIX);
 776                 } else {
 777                         bmap->avail = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL0_RADIX);
 778                 }
 779                 key += H2FMSHIFT(HAMMER2_FREEMAP_LEVEL0_RADIX);
 780                 ++bmap;
 781         }
 782 }
 783
 784 /*
 785  * The current Level 1 freemap has been exhausted, iterate to the next
 786  * one, return ENOSPC if no freemaps remain.
 787  *
 788  * XXX this should rotate back to the beginning to handle freed-up space
 789  * XXX or use intermediate entries to locate free space. TODO
 790  */
 791 static int
 792 hammer2_freemap_iterate(hammer2_chain_t **parentp, hammer2_chain_t **chainp,
 793                         hammer2_fiterate_t *iter)
 794 {
 795         hammer2_dev_t *hmp = (*parentp)->hmp;
 796
 797         iter->bnext &= ~(H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX) - 1);
 798         iter->bnext += H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
 799         if (iter->bnext >= hmp->voldata.volu_size) {
 800                 iter->bnext = 0;
 801                 if (++iter->loops == 2)
 802                         return (ENOSPC);
 803         }
 804         return(EAGAIN);
 805 }
 806
 807 /*
 808  * Adjust the bit-pattern for data in the freemap bitmap according to
 809  * (how).  This code is called from on-mount recovery to fixup (mark
 810  * as allocated) blocks whos freemap upates might not have been committed
 811  * in the last crash and is used by the bulk freemap scan to stage frees.
 812  *
 813  * XXX currently disabled when how == 0 (the normal real-time case).  At
 814  * the moment we depend on the bulk freescan to actually free blocks.  It
 815  * will still call this routine with a non-zero how to stage possible frees
 816  * and to do the actual free.
 817  */
 818 void
 819 hammer2_freemap_adjust(hammer2_dev_t *hmp, hammer2_blockref_t *bref,
 820                        int how)
 821 {
 822         hammer2_off_t data_off = bref->data_off;
 823         hammer2_chain_t *chain;
 824         hammer2_chain_t *parent;
 825         hammer2_bmap_data_t *bmap;
 826         hammer2_key_t key;
 827         hammer2_key_t key_dummy;
 828         hammer2_off_t l0size;
 829         hammer2_off_t l1size;
 830         hammer2_off_t l1mask;
 831         hammer2_tid_t mtid;
 832         hammer2_bitmap_t *bitmap;
 833         const hammer2_bitmap_t bmmask00 = 0;
 834         hammer2_bitmap_t bmmask01;
 835         hammer2_bitmap_t bmmask10;
 836         hammer2_bitmap_t bmmask11;
 837         size_t bytes;
 838         uint16_t class;
 839         int radix;
 840         int start;
 841         int count;
 842         int modified = 0;
 843         int cache_index = -1;
 844         int error;
 845
 846         KKASSERT(how == HAMMER2_FREEMAP_DORECOVER);
 847
 848         mtid = hammer2_trans_sub(hmp->spmp);
 849
 850         radix = (int)data_off & HAMMER2_OFF_MASK_RADIX;
 851         data_off &= ~HAMMER2_OFF_MASK_RADIX;
 852         KKASSERT(radix <= HAMMER2_RADIX_MAX);
 853
 854         bytes = (size_t)1 << radix;
 855         class = (bref->type << 8) | hammer2_devblkradix(radix);
 856
 857         /*
 858          * We can't adjust thre freemap for data allocations made by
 859          * newfs_hammer2.
 860          */
 861         if (data_off < hmp->voldata.allocator_beg)
 862                 return;
 863
 864         KKASSERT((data_off & HAMMER2_ZONE_MASK64) >= HAMMER2_ZONE_SEG);
 865
 866         /*
 867          * Lookup the level1 freemap chain.  The chain must exist.
 868          */
 869         key = H2FMBASE(data_off, HAMMER2_FREEMAP_LEVEL1_RADIX);
 870         l0size = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL0_RADIX);
 871         l1size = H2FMSHIFT(HAMMER2_FREEMAP_LEVEL1_RADIX);
 872         l1mask = l1size - 1;
 873
 874         parent = &hmp->fchain;
 875         hammer2_chain_ref(parent);
 876         hammer2_chain_lock(parent, HAMMER2_RESOLVE_ALWAYS);
 877
 878         chain = hammer2_chain_lookup(&parent, &key_dummy, key, key + l1mask,
 879                                      &cache_index,
 880                                      HAMMER2_LOOKUP_ALWAYS |
 881                                      HAMMER2_LOOKUP_MATCHIND);
 882
 883         /*
 884          * Stop early if we are trying to free something but no leaf exists.
 885          */
 886         if (chain == NULL && how != HAMMER2_FREEMAP_DORECOVER) {
 887                 kprintf("hammer2_freemap_adjust: %016jx: no chain\n",
 888                         (intmax_t)bref->data_off);
 889                 goto done;
 890         }
 891         if (chain->error) {
 892                 kprintf("hammer2_freemap_adjust: %016jx: error %s\n",
 893                         (intmax_t)bref->data_off,
 894                         hammer2_error_str(chain->error));
 895                 hammer2_chain_unlock(chain);
 896                 hammer2_chain_drop(chain);
 897                 chain = NULL;
 898                 goto done;
 899         }
 900
 901         /*
 902          * Create any missing leaf(s) if we are doing a recovery (marking
 903          * the block(s) as being allocated instead of being freed).  Be sure
 904          * to initialize the auxillary freemap tracking info in the
 905          * bref.check.freemap structure.
 906          */
 907         if (chain == NULL && how == HAMMER2_FREEMAP_DORECOVER) {
 908                 error = hammer2_chain_create(&parent, &chain, hmp->spmp,
 909                                      key, HAMMER2_FREEMAP_LEVEL1_RADIX,
 910                                      HAMMER2_BREF_TYPE_FREEMAP_LEAF,
 911                                      HAMMER2_FREEMAP_LEVELN_PSIZE,
 912                                      mtid, 0);
 913
 914                 if (hammer2_debug & 0x0040) {
 915                         kprintf("fixup create chain %p %016jx:%d\n",
 916                                 chain, chain->bref.key, chain->bref.keybits);
 917                 }
 918
 919                 if (error == 0) {
 920                         hammer2_chain_modify(chain, mtid, 0);
 921                         bzero(&chain->data->bmdata[0],
 922                               HAMMER2_FREEMAP_LEVELN_PSIZE);
 923                         chain->bref.check.freemap.bigmask = (uint32_t)-1;
 924                         chain->bref.check.freemap.avail = l1size;
 925                         /* bref.methods should already be inherited */
 926
 927                         hammer2_freemap_init(hmp, key, chain);
 928                 }
 929                 /* XXX handle error */
 930         }
 931
 932 #if FREEMAP_DEBUG
 933         kprintf("FREEMAP ADJUST TYPE %d %016jx/%d DATA_OFF=%016jx\n",
 934                 chain->bref.type, chain->bref.key,
 935                 chain->bref.keybits, chain->bref.data_off);
 936 #endif
 937
 938         /*
 939          * Calculate the bitmask (runs in 2-bit pairs).
 940          */
 941         start = ((int)(data_off >> HAMMER2_FREEMAP_BLOCK_RADIX) & 15) * 2;
 942         bmmask01 = (hammer2_bitmap_t)1 << start;
 943         bmmask10 = (hammer2_bitmap_t)2 << start;
 944         bmmask11 = (hammer2_bitmap_t)3 << start;
 945
 946         /*
 947          * Fixup the bitmap.  Partial blocks cannot be fully freed unless
 948          * a bulk scan is able to roll them up.
 949          */
 950         if (radix < HAMMER2_FREEMAP_BLOCK_RADIX) {
 951                 count = 1;
 952                 if (how == HAMMER2_FREEMAP_DOREALFREE)
 953                         how = HAMMER2_FREEMAP_DOMAYFREE;
 954         } else {
 955                 count = 1 << (radix - HAMMER2_FREEMAP_BLOCK_RADIX);
 956         }
 957
 958         /*
 959          * [re]load the bmap and bitmap pointers.  Each bmap entry covers
 960          * a 2MB swath.  The bmap itself (LEVEL1) covers 2GB.
 961          *
 962          * Be sure to reset the linear iterator to ensure that the adjustment
 963          * is not ignored.
 964          */
 965 again:
 966         bmap = &chain->data->bmdata[(int)(data_off >> HAMMER2_SEGRADIX) &
 967                                     (HAMMER2_FREEMAP_COUNT - 1)];
 968         bitmap = &bmap->bitmapq[(int)(data_off >> (HAMMER2_SEGRADIX - 3)) & 7];
 969
 970         if (modified)
 971                 bmap->linear = 0;
 972
 973         while (count) {
 974                 KKASSERT(bmmask11);
 975                 if (how == HAMMER2_FREEMAP_DORECOVER) {
 976                         /*
 977                          * Recovery request, mark as allocated.
 978                          */
 979                         if ((*bitmap & bmmask11) != bmmask11) {
 980                                 if (modified == 0) {
 981                                         hammer2_chain_modify(chain, mtid, 0);
 982                                         modified = 1;
 983                                         goto again;
 984                                 }
 985                                 if ((*bitmap & bmmask11) == bmmask00) {
 986                                         bmap->avail -=
 987                                                 HAMMER2_FREEMAP_BLOCK_SIZE;
 988                                 }
 989                                 if (bmap->class == 0)
 990                                         bmap->class = class;
 991                                 *bitmap |= bmmask11;
 992                                 if (hammer2_debug & 0x0040) {
 993                                         kprintf("hammer2_freemap_recover: "
 994                                                 "fixup type=%02x "
 995                                                 "block=%016jx/%zd\n",
 996                                                 bref->type, data_off, bytes);
 997                                 }
 998                         } else {
 999                                 /*
1000                                 kprintf("hammer2_freemap_recover:  good "
1001                                         "type=%02x block=%016jx/%zd\n",
1002                                         bref->type, data_off, bytes);
1003                                 */
1004                         }
1005                 }
1006 #if 0
1007                 /*
1008                  * XXX this stuff doesn't work, avail is miscalculated and
1009                  * code 10 means something else now.
1010                  */
1011                 else if ((*bitmap & bmmask11) == bmmask11) {
1012                         /*
1013                          * Mayfree/Realfree request and bitmap is currently
1014                          * marked as being fully allocated.
1015                          */
1016                         if (!modified) {
1017                                 hammer2_chain_modify(chain, 0);
1018                                 modified = 1;
1019                                 goto again;
1020                         }
1021                         if (how == HAMMER2_FREEMAP_DOREALFREE)
1022                                 *bitmap &= ~bmmask11;
1023                         else
1024                                 *bitmap = (*bitmap & ~bmmask11) | bmmask10;
1025                 } else if ((*bitmap & bmmask11) == bmmask10) {
1026                         /*
1027                          * Mayfree/Realfree request and bitmap is currently
1028                          * marked as being possibly freeable.
1029                          */
1030                         if (how == HAMMER2_FREEMAP_DOREALFREE) {
1031                                 if (!modified) {
1032                                         hammer2_chain_modify(chain, 0);
1033                                         modified = 1;
1034                                         goto again;
1035                                 }
1036                                 *bitmap &= ~bmmask11;
1037                         }
1038                 } else {
1039                         /*
1040                          * 01 - Not implemented, currently illegal state
1041                          * 00 - Not allocated at all, illegal free.
1042                          */
1043                         panic("hammer2_freemap_adjust: "
1044                               "Illegal state %08x(%08x)",
1045                               *bitmap, *bitmap & bmmask11);
1046                 }
1047 #endif
1048                 --count;
1049                 bmmask01 <<= 2;
1050                 bmmask10 <<= 2;
1051                 bmmask11 <<= 2;
1052         }
1053 #if HAMMER2_BMAP_ELEMENTS != 8
1054 #error "hammer2_freemap.c: HAMMER2_BMAP_ELEMENTS expected to be 8"
1055 #endif
1056         if (how == HAMMER2_FREEMAP_DOREALFREE && modified) {
1057                 bmap->avail += 1 << radix;
1058                 KKASSERT(bmap->avail <= HAMMER2_SEGSIZE);
1059                 if (bmap->avail == HAMMER2_SEGSIZE &&
1060                     bmap->bitmapq[0] == 0 &&
1061                     bmap->bitmapq[1] == 0 &&
1062                     bmap->bitmapq[2] == 0 &&
1063                     bmap->bitmapq[3] == 0 &&
1064                     bmap->bitmapq[4] == 0 &&
1065                     bmap->bitmapq[5] == 0 &&
1066                     bmap->bitmapq[6] == 0 &&
1067                     bmap->bitmapq[7] == 0) {
1068                         key = H2FMBASE(data_off, HAMMER2_FREEMAP_LEVEL0_RADIX);
1069                         kprintf("Freeseg %016jx\n", (intmax_t)key);
1070                         bmap->class = 0;
1071                 }
1072         }
1073
1074         /*
1075          * chain->bref.check.freemap.bigmask (XXX)
1076          *
1077          * Setting bigmask is a hint to the allocation code that there might
1078          * be something allocatable.  We also set this in recovery... it
1079          * doesn't hurt and we might want to use the hint for other validation
1080          * operations later on.
1081          */
1082         if (modified)
1083                 chain->bref.check.freemap.bigmask |= 1 << radix;
1084
1085         hammer2_chain_unlock(chain);
1086         hammer2_chain_drop(chain);
1087 done:
1088         hammer2_chain_unlock(parent);
1089         hammer2_chain_drop(parent);
1090 }
1091
1092 /*
1093  * Validate the freemap, in three stages.
1094  *
1095  * stage-1      ALLOCATED     -> POSSIBLY FREE
1096  *              POSSIBLY FREE -> POSSIBLY FREE (type corrected)
1097  *
1098  *      This transitions bitmap entries from ALLOCATED to POSSIBLY FREE.
1099  *      The POSSIBLY FREE state does not mean that a block is actually free
1100  *      and may be transitioned back to ALLOCATED in stage-2.
1101  *
1102  *      This is typically done during normal filesystem operations when
1103  *      something is deleted or a block is replaced.
1104  *
1105  *      This is done by bulkfree in-bulk after a memory-bounded meta-data
1106  *      scan to try to determine what might be freeable.
1107  *
1108  *      This can be done unconditionally through a freemap scan when the
1109  *      intention is to brute-force recover the proper state of the freemap.
1110  *
1111  * stage-2      POSSIBLY FREE -> ALLOCATED      (scan metadata topology)
1112  *
1113  *      This is done by bulkfree during a meta-data scan to ensure that
1114  *      all blocks still actually allocated by the filesystem are marked
1115  *      as such.
1116  *
1117  *      NOTE! Live filesystem transitions to POSSIBLY FREE can occur while
1118  *            the bulkfree stage-2 and stage-3 is running.  The live filesystem
1119  *            will use the alternative POSSIBLY FREE type (2) to prevent
1120  *            stage-3 from improperly transitioning unvetted possibly-free
1121  *            blocks to FREE.
1122  *
1123  * stage-3      POSSIBLY FREE (type 1) -> FREE  (scan freemap)
1124  *
1125  *      This is done by bulkfree to finalize POSSIBLY FREE states.
1126  *
1127  */