usr.sbin/makefs/ffs/ffs_alloc.c

   1 /*      $NetBSD: ffs_alloc.c,v 1.28 2015/03/29 05:52:59 agc Exp $       */
   2 /* From: NetBSD: ffs_alloc.c,v 1.50 2001/09/06 02:16:01 lukem Exp */
   3
   4 /*
   5  * Copyright (c) 2002 Networks Associates Technology, Inc.
   6  * All rights reserved.
   7  *
   8  * This software was developed for the FreeBSD Project by Marshall
   9  * Kirk McKusick and Network Associates Laboratories, the Security
  10  * Research Division of Network Associates, Inc. under DARPA/SPAWAR
  11  * contract N66001-01-C-8035 ("CBOSS"), as part of the DARPA CHATS
  12  * research program
  13  *
  14  * Copyright (c) 1982, 1986, 1989, 1993
  15  *      The Regents of the University of California.  All rights reserved.
  16  *
  17  * Redistribution and use in source and binary forms, with or without
  18  * modification, are permitted provided that the following conditions
  19  * are met:
  20  * 1. Redistributions of source code must retain the above copyright
  21  *    notice, this list of conditions and the following disclaimer.
  22  * 2. Redistributions in binary form must reproduce the above copyright
  23  *    notice, this list of conditions and the following disclaimer in the
  24  *    documentation and/or other materials provided with the distribution.
  25  * 3. Neither the name of the University nor the names of its contributors
  26  *    may be used to endorse or promote products derived from this software
  27  *    without specific prior written permission.
  28  *
  29  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  30  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  31  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  32  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  33  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  34  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  35  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  36  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  37  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  38  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  39  * SUCH DAMAGE.
  40  *
  41  *      @(#)ffs_alloc.c 8.19 (Berkeley) 7/13/95
  42  */
  43
  44 #if HAVE_NBTOOL_CONFIG_H
  45 #include "nbtool_config.h"
  46 #endif
  47
  48 #include <sys/cdefs.h>
  49 #if defined(__RCSID) && !defined(__lint)
  50 __RCSID("$NetBSD: ffs_alloc.c,v 1.28 2015/03/29 05:52:59 agc Exp $");
  51 #endif  /* !__lint */
  52
  53 #include <sys/param.h>
  54 #include <sys/time.h>
  55
  56 #include <errno.h>
  57
  58 #include "makefs.h"
  59
  60 #include <ufs/ufs/dinode.h>
  61 #include <ufs/ufs/ufs_bswap.h>
  62 #include <ufs/ffs/fs.h>
  63
  64 #include "ffs/buf.h"
  65 #include "ffs/ufs_inode.h"
  66 #include "ffs/ffs_extern.h"
  67
  68
  69 static int scanc(u_int, const u_char *, const u_char *, int);
  70
  71 static daddr_t ffs_alloccg(struct inode *, int, daddr_t, int);
  72 static daddr_t ffs_alloccgblk(struct inode *, struct buf *, daddr_t);
  73 static daddr_t ffs_hashalloc(struct inode *, int, daddr_t, int,
  74                      daddr_t (*)(struct inode *, int, daddr_t, int));
  75 static int32_t ffs_mapsearch(struct fs *, struct cg *, daddr_t, int);
  76
  77 /* in ffs_tables.c */
  78 extern const int inside[], around[];
  79 extern const u_char * const fragtbl[];
  80
  81 /*
  82  * Allocate a block in the file system.
  83  *
  84  * The size of the requested block is given, which must be some
  85  * multiple of fs_fsize and <= fs_bsize.
  86  * A preference may be optionally specified. If a preference is given
  87  * the following hierarchy is used to allocate a block:
  88  *   1) allocate the requested block.
  89  *   2) allocate a rotationally optimal block in the same cylinder.
  90  *   3) allocate a block in the same cylinder group.
  91  *   4) quadradically rehash into other cylinder groups, until an
  92  *      available block is located.
  93  * If no block preference is given the following hierarchy is used
  94  * to allocate a block:
  95  *   1) allocate a block in the cylinder group that contains the
  96  *      inode for the file.
  97  *   2) quadradically rehash into other cylinder groups, until an
  98  *      available block is located.
  99  */
 100 int
 101 ffs_alloc(struct inode *ip, daddr_t lbn __unused, daddr_t bpref, int size,
 102     daddr_t *bnp)
 103 {
 104         struct fs *fs = ip->i_fs;
 105         daddr_t bno;
 106         int cg;
 107
 108         *bnp = 0;
 109         if (size > fs->fs_bsize || ffs_fragoff(fs, size) != 0) {
 110                 errx(1, "ffs_alloc: bad size: bsize %d size %d",
 111                     fs->fs_bsize, size);
 112         }
 113         if (size == fs->fs_bsize && fs->fs_cstotal.cs_nbfree == 0)
 114                 goto nospace;
 115         if (bpref >= fs->fs_size)
 116                 bpref = 0;
 117         if (bpref == 0)
 118                 cg = ino_to_cg(fs, ip->i_number);
 119         else
 120                 cg = dtog(fs, bpref);
 121         bno = ffs_hashalloc(ip, cg, bpref, size, ffs_alloccg);
 122         if (bno > 0) {
 123                 DIP_ADD(ip, blocks, size / DEV_BSIZE);
 124                 *bnp = bno;
 125                 return (0);
 126         }
 127 nospace:
 128         return (ENOSPC);
 129 }
 130
 131 /*
 132  * Select the desired position for the next block in a file.  The file is
 133  * logically divided into sections. The first section is composed of the
 134  * direct blocks. Each additional section contains fs_maxbpg blocks.
 135  *
 136  * If no blocks have been allocated in the first section, the policy is to
 137  * request a block in the same cylinder group as the inode that describes
 138  * the file. If no blocks have been allocated in any other section, the
 139  * policy is to place the section in a cylinder group with a greater than
 140  * average number of free blocks.  An appropriate cylinder group is found
 141  * by using a rotor that sweeps the cylinder groups. When a new group of
 142  * blocks is needed, the sweep begins in the cylinder group following the
 143  * cylinder group from which the previous allocation was made. The sweep
 144  * continues until a cylinder group with greater than the average number
 145  * of free blocks is found. If the allocation is for the first block in an
 146  * indirect block, the information on the previous allocation is unavailable;
 147  * here a best guess is made based upon the logical block number being
 148  * allocated.
 149  *
 150  * If a section is already partially allocated, the policy is to
 151  * contiguously allocate fs_maxcontig blocks.  The end of one of these
 152  * contiguous blocks and the beginning of the next is physically separated
 153  * so that the disk head will be in transit between them for at least
 154  * fs_rotdelay milliseconds.  This is to allow time for the processor to
 155  * schedule another I/O transfer.
 156  */
 157 /* XXX ondisk32 */
 158 daddr_t
 159 ffs_blkpref_ufs1(struct inode *ip, daddr_t lbn, int indx, int32_t *bap)
 160 {
 161         struct fs *fs;
 162         int cg;
 163         int avgbfree, startcg;
 164
 165         fs = ip->i_fs;
 166         if (indx % fs->fs_maxbpg == 0 || bap[indx - 1] == 0) {
 167                 if (lbn < UFS_NDADDR + FFS_NINDIR(fs)) {
 168                         cg = ino_to_cg(fs, ip->i_number);
 169                         return (fs->fs_fpg * cg + fs->fs_frag);
 170                 }
 171                 /*
 172                  * Find a cylinder with greater than average number of
 173                  * unused data blocks.
 174                  */
 175                 if (indx == 0 || bap[indx - 1] == 0)
 176                         startcg =
 177                             ino_to_cg(fs, ip->i_number) + lbn / fs->fs_maxbpg;
 178                 else
 179                         startcg = dtog(fs,
 180                                 ufs_rw32(bap[indx - 1], UFS_FSNEEDSWAP(fs)) + 1);
 181                 startcg %= fs->fs_ncg;
 182                 avgbfree = fs->fs_cstotal.cs_nbfree / fs->fs_ncg;
 183                 for (cg = startcg; cg < fs->fs_ncg; cg++)
 184                         if (fs->fs_cs(fs, cg).cs_nbfree >= avgbfree)
 185                                 return (fs->fs_fpg * cg + fs->fs_frag);
 186                 for (cg = 0; cg <= startcg; cg++)
 187                         if (fs->fs_cs(fs, cg).cs_nbfree >= avgbfree)
 188                                 return (fs->fs_fpg * cg + fs->fs_frag);
 189                 return (0);
 190         }
 191         /*
 192          * We just always try to lay things out contiguously.
 193          */
 194         return ufs_rw32(bap[indx - 1], UFS_FSNEEDSWAP(fs)) + fs->fs_frag;
 195 }
 196
 197 daddr_t
 198 ffs_blkpref_ufs2(struct inode *ip, daddr_t lbn, int indx, int64_t *bap)
 199 {
 200         struct fs *fs;
 201         int cg;
 202         int avgbfree, startcg;
 203
 204         fs = ip->i_fs;
 205         if (indx % fs->fs_maxbpg == 0 || bap[indx - 1] == 0) {
 206                 if (lbn < UFS_NDADDR + FFS_NINDIR(fs)) {
 207                         cg = ino_to_cg(fs, ip->i_number);
 208                         return (fs->fs_fpg * cg + fs->fs_frag);
 209                 }
 210                 /*
 211                  * Find a cylinder with greater than average number of
 212                  * unused data blocks.
 213                  */
 214                 if (indx == 0 || bap[indx - 1] == 0)
 215                         startcg =
 216                             ino_to_cg(fs, ip->i_number) + lbn / fs->fs_maxbpg;
 217                 else
 218                         startcg = dtog(fs,
 219                                 ufs_rw64(bap[indx - 1], UFS_FSNEEDSWAP(fs)) + 1);
 220                 startcg %= fs->fs_ncg;
 221                 avgbfree = fs->fs_cstotal.cs_nbfree / fs->fs_ncg;
 222                 for (cg = startcg; cg < fs->fs_ncg; cg++)
 223                         if (fs->fs_cs(fs, cg).cs_nbfree >= avgbfree) {
 224                                 return (fs->fs_fpg * cg + fs->fs_frag);
 225                         }
 226                 for (cg = 0; cg < startcg; cg++)
 227                         if (fs->fs_cs(fs, cg).cs_nbfree >= avgbfree) {
 228                                 return (fs->fs_fpg * cg + fs->fs_frag);
 229                         }
 230                 return (0);
 231         }
 232         /*
 233          * We just always try to lay things out contiguously.
 234          */
 235         return ufs_rw64(bap[indx - 1], UFS_FSNEEDSWAP(fs)) + fs->fs_frag;
 236 }
 237
 238 /*
 239  * Implement the cylinder overflow algorithm.
 240  *
 241  * The policy implemented by this algorithm is:
 242  *   1) allocate the block in its requested cylinder group.
 243  *   2) quadradically rehash on the cylinder group number.
 244  *   3) brute force search for a free block.
 245  *
 246  * `size':      size for data blocks, mode for inodes
 247  */
 248 /*VARARGS5*/
 249 static daddr_t
 250 ffs_hashalloc(struct inode *ip, int cg, daddr_t pref, int size,
 251     daddr_t (*allocator)(struct inode *, int, daddr_t, int))
 252 {
 253         struct fs *fs;
 254         daddr_t result;
 255         int i, icg = cg;
 256
 257         fs = ip->i_fs;
 258         /*
 259          * 1: preferred cylinder group
 260          */
 261         result = (*allocator)(ip, cg, pref, size);
 262         if (result)
 263                 return (result);
 264         /*
 265          * 2: quadratic rehash
 266          */
 267         for (i = 1; i < fs->fs_ncg; i *= 2) {
 268                 cg += i;
 269                 if (cg >= fs->fs_ncg)
 270                         cg -= fs->fs_ncg;
 271                 result = (*allocator)(ip, cg, 0, size);
 272                 if (result)
 273                         return (result);
 274         }
 275         /*
 276          * 3: brute force search
 277          * Note that we start at i == 2, since 0 was checked initially,
 278          * and 1 is always checked in the quadratic rehash.
 279          */
 280         cg = (icg + 2) % fs->fs_ncg;
 281         for (i = 2; i < fs->fs_ncg; i++) {
 282                 result = (*allocator)(ip, cg, 0, size);
 283                 if (result)
 284                         return (result);
 285                 cg++;
 286                 if (cg == fs->fs_ncg)
 287                         cg = 0;
 288         }
 289         return (0);
 290 }
 291
 292 /*
 293  * Determine whether a block can be allocated.
 294  *
 295  * Check to see if a block of the appropriate size is available,
 296  * and if it is, allocate it.
 297  */
 298 static daddr_t
 299 ffs_alloccg(struct inode *ip, int cg, daddr_t bpref, int size)
 300 {
 301         struct cg *cgp;
 302         struct buf *bp;
 303         daddr_t bno, blkno;
 304         int error, frags, allocsiz, i;
 305         struct fs *fs = ip->i_fs;
 306         const int needswap = UFS_FSNEEDSWAP(fs);
 307
 308         if (fs->fs_cs(fs, cg).cs_nbfree == 0 && size == fs->fs_bsize)
 309                 return (0);
 310         error = bread(ip->i_devvp, FFS_FSBTODB(fs, cgtod(fs, cg)),
 311             (int)fs->fs_cgsize, 0, &bp);
 312         if (error) {
 313                 return (0);
 314         }
 315         cgp = (struct cg *)bp->b_data;
 316         if (!cg_chkmagic(cgp, needswap) ||
 317             (cgp->cg_cs.cs_nbfree == 0 && size == fs->fs_bsize)) {
 318                 brelse(bp, 0);
 319                 return (0);
 320         }
 321         if (size == fs->fs_bsize) {
 322                 bno = ffs_alloccgblk(ip, bp, bpref);
 323                 bwrite(bp);
 324                 return (bno);
 325         }
 326         /*
 327          * check to see if any fragments are already available
 328          * allocsiz is the size which will be allocated, hacking
 329          * it down to a smaller size if necessary
 330          */
 331         frags = ffs_numfrags(fs, size);
 332         for (allocsiz = frags; allocsiz < fs->fs_frag; allocsiz++)
 333                 if (cgp->cg_frsum[allocsiz] != 0)
 334                         break;
 335         if (allocsiz == fs->fs_frag) {
 336                 /*
 337                  * no fragments were available, so a block will be
 338                  * allocated, and hacked up
 339                  */
 340                 if (cgp->cg_cs.cs_nbfree == 0) {
 341                         brelse(bp, 0);
 342                         return (0);
 343                 }
 344                 bno = ffs_alloccgblk(ip, bp, bpref);
 345                 bpref = dtogd(fs, bno);
 346                 for (i = frags; i < fs->fs_frag; i++)
 347                         setbit(cg_blksfree(cgp, needswap), bpref + i);
 348                 i = fs->fs_frag - frags;
 349                 ufs_add32(cgp->cg_cs.cs_nffree, i, needswap);
 350                 fs->fs_cstotal.cs_nffree += i;
 351                 fs->fs_cs(fs, cg).cs_nffree += i;
 352                 fs->fs_fmod = 1;
 353                 ufs_add32(cgp->cg_frsum[i], 1, needswap);
 354                 bdwrite(bp);
 355                 return (bno);
 356         }
 357         bno = ffs_mapsearch(fs, cgp, bpref, allocsiz);
 358         for (i = 0; i < frags; i++)
 359                 clrbit(cg_blksfree(cgp, needswap), bno + i);
 360         ufs_add32(cgp->cg_cs.cs_nffree, -frags, needswap);
 361         fs->fs_cstotal.cs_nffree -= frags;
 362         fs->fs_cs(fs, cg).cs_nffree -= frags;
 363         fs->fs_fmod = 1;
 364         ufs_add32(cgp->cg_frsum[allocsiz], -1, needswap);
 365         if (frags != allocsiz)
 366                 ufs_add32(cgp->cg_frsum[allocsiz - frags], 1, needswap);
 367         blkno = cg * fs->fs_fpg + bno;
 368         bdwrite(bp);
 369         return blkno;
 370 }
 371
 372 /*
 373  * Allocate a block in a cylinder group.
 374  *
 375  * This algorithm implements the following policy:
 376  *   1) allocate the requested block.
 377  *   2) allocate a rotationally optimal block in the same cylinder.
 378  *   3) allocate the next available block on the block rotor for the
 379  *      specified cylinder group.
 380  * Note that this routine only allocates fs_bsize blocks; these
 381  * blocks may be fragmented by the routine that allocates them.
 382  */
 383 static daddr_t
 384 ffs_alloccgblk(struct inode *ip, struct buf *bp, daddr_t bpref)
 385 {
 386         struct cg *cgp;
 387         daddr_t blkno;
 388         int32_t bno;
 389         struct fs *fs = ip->i_fs;
 390         const int needswap = UFS_FSNEEDSWAP(fs);
 391         u_int8_t *blksfree;
 392
 393         cgp = (struct cg *)bp->b_data;
 394         blksfree = cg_blksfree(cgp, needswap);
 395         if (bpref == 0 || dtog(fs, bpref) != ufs_rw32(cgp->cg_cgx, needswap)) {
 396                 bpref = ufs_rw32(cgp->cg_rotor, needswap);
 397         } else {
 398                 bpref = ffs_blknum(fs, bpref);
 399                 bno = dtogd(fs, bpref);
 400                 /*
 401                  * if the requested block is available, use it
 402                  */
 403                 if (ffs_isblock(fs, blksfree, ffs_fragstoblks(fs, bno)))
 404                         goto gotit;
 405         }
 406         /*
 407          * Take the next available one in this cylinder group.
 408          */
 409         bno = ffs_mapsearch(fs, cgp, bpref, (int)fs->fs_frag);
 410         if (bno < 0)
 411                 return (0);
 412         cgp->cg_rotor = ufs_rw32(bno, needswap);
 413 gotit:
 414         blkno = ffs_fragstoblks(fs, bno);
 415         ffs_clrblock(fs, blksfree, (long)blkno);
 416         ffs_clusteracct(fs, cgp, blkno, -1);
 417         ufs_add32(cgp->cg_cs.cs_nbfree, -1, needswap);
 418         fs->fs_cstotal.cs_nbfree--;
 419         fs->fs_cs(fs, ufs_rw32(cgp->cg_cgx, needswap)).cs_nbfree--;
 420         fs->fs_fmod = 1;
 421         blkno = ufs_rw32(cgp->cg_cgx, needswap) * fs->fs_fpg + bno;
 422         return (blkno);
 423 }
 424
 425 /*
 426  * Free a block or fragment.
 427  *
 428  * The specified block or fragment is placed back in the
 429  * free map. If a fragment is deallocated, a possible
 430  * block reassembly is checked.
 431  */
 432 void
 433 ffs_blkfree(struct inode *ip, daddr_t bno, long size)
 434 {
 435         struct cg *cgp;
 436         struct buf *bp;
 437         int32_t fragno, cgbno;
 438         int i, error, cg, blk, frags, bbase;
 439         struct fs *fs = ip->i_fs;
 440         const int needswap = UFS_FSNEEDSWAP(fs);
 441
 442         if (size > fs->fs_bsize || ffs_fragoff(fs, size) != 0 ||
 443             ffs_fragnum(fs, bno) + ffs_numfrags(fs, size) > fs->fs_frag) {
 444                 errx(1, "blkfree: bad size: bno %lld bsize %d size %ld",
 445                     (long long)bno, fs->fs_bsize, size);
 446         }
 447         cg = dtog(fs, bno);
 448         if (bno >= fs->fs_size) {
 449                 warnx("bad block %lld, ino %llu", (long long)bno,
 450                     (unsigned long long)ip->i_number);
 451                 return;
 452         }
 453         error = bread(ip->i_devvp, FFS_FSBTODB(fs, cgtod(fs, cg)),
 454             (int)fs->fs_cgsize, 0, &bp);
 455         if (error) {
 456                 brelse(bp, 0);
 457                 return;
 458         }
 459         cgp = (struct cg *)bp->b_data;
 460         if (!cg_chkmagic(cgp, needswap)) {
 461                 brelse(bp, 0);
 462                 return;
 463         }
 464         cgbno = dtogd(fs, bno);
 465         if (size == fs->fs_bsize) {
 466                 fragno = ffs_fragstoblks(fs, cgbno);
 467                 if (!ffs_isfreeblock(fs, cg_blksfree(cgp, needswap), fragno)) {
 468                         errx(1, "blkfree: freeing free block %lld",
 469                             (long long)bno);
 470                 }
 471                 ffs_setblock(fs, cg_blksfree(cgp, needswap), fragno);
 472                 ffs_clusteracct(fs, cgp, fragno, 1);
 473                 ufs_add32(cgp->cg_cs.cs_nbfree, 1, needswap);
 474                 fs->fs_cstotal.cs_nbfree++;
 475                 fs->fs_cs(fs, cg).cs_nbfree++;
 476         } else {
 477                 bbase = cgbno - ffs_fragnum(fs, cgbno);
 478                 /*
 479                  * decrement the counts associated with the old frags
 480                  */
 481                 blk = blkmap(fs, cg_blksfree(cgp, needswap), bbase);
 482                 ffs_fragacct(fs, blk, cgp->cg_frsum, -1, needswap);
 483                 /*
 484                  * deallocate the fragment
 485                  */
 486                 frags = ffs_numfrags(fs, size);
 487                 for (i = 0; i < frags; i++) {
 488                         if (isset(cg_blksfree(cgp, needswap), cgbno + i)) {
 489                                 errx(1, "blkfree: freeing free frag: block %lld",
 490                                     (long long)(cgbno + i));
 491                         }
 492                         setbit(cg_blksfree(cgp, needswap), cgbno + i);
 493                 }
 494                 ufs_add32(cgp->cg_cs.cs_nffree, i, needswap);
 495                 fs->fs_cstotal.cs_nffree += i;
 496                 fs->fs_cs(fs, cg).cs_nffree += i;
 497                 /*
 498                  * add back in counts associated with the new frags
 499                  */
 500                 blk = blkmap(fs, cg_blksfree(cgp, needswap), bbase);
 501                 ffs_fragacct(fs, blk, cgp->cg_frsum, 1, needswap);
 502                 /*
 503                  * if a complete block has been reassembled, account for it
 504                  */
 505                 fragno = ffs_fragstoblks(fs, bbase);
 506                 if (ffs_isblock(fs, cg_blksfree(cgp, needswap), fragno)) {
 507                         ufs_add32(cgp->cg_cs.cs_nffree, -fs->fs_frag, needswap);
 508                         fs->fs_cstotal.cs_nffree -= fs->fs_frag;
 509                         fs->fs_cs(fs, cg).cs_nffree -= fs->fs_frag;
 510                         ffs_clusteracct(fs, cgp, fragno, 1);
 511                         ufs_add32(cgp->cg_cs.cs_nbfree, 1, needswap);
 512                         fs->fs_cstotal.cs_nbfree++;
 513                         fs->fs_cs(fs, cg).cs_nbfree++;
 514                 }
 515         }
 516         fs->fs_fmod = 1;
 517         bdwrite(bp);
 518 }
 519
 520
 521 static int
 522 scanc(u_int size, const u_char *cp, const u_char table[], int mask)
 523 {
 524         const u_char *end = &cp[size];
 525
 526         while (cp < end && (table[*cp] & mask) == 0)
 527                 cp++;
 528         return (end - cp);
 529 }
 530
 531 /*
 532  * Find a block of the specified size in the specified cylinder group.
 533  *
 534  * It is a panic if a request is made to find a block if none are
 535  * available.
 536  */
 537 static int32_t
 538 ffs_mapsearch(struct fs *fs, struct cg *cgp, daddr_t bpref, int allocsiz)
 539 {
 540         int32_t bno;
 541         int start, len, loc, i;
 542         int blk, field, subfield, pos;
 543         int ostart, olen;
 544         const int needswap = UFS_FSNEEDSWAP(fs);
 545
 546         /*
 547          * find the fragment by searching through the free block
 548          * map for an appropriate bit pattern
 549          */
 550         if (bpref)
 551                 start = dtogd(fs, bpref) / NBBY;
 552         else
 553                 start = ufs_rw32(cgp->cg_frotor, needswap) / NBBY;
 554         len = howmany(fs->fs_fpg, NBBY) - start;
 555         ostart = start;
 556         olen = len;
 557         loc = scanc((u_int)len,
 558                 (const u_char *)&cg_blksfree(cgp, needswap)[start],
 559                 (const u_char *)fragtbl[fs->fs_frag],
 560                 (1 << (allocsiz - 1 + (fs->fs_frag % NBBY))));
 561         if (loc == 0) {
 562                 len = start + 1;
 563                 start = 0;
 564                 loc = scanc((u_int)len,
 565                         (const u_char *)&cg_blksfree(cgp, needswap)[0],
 566                         (const u_char *)fragtbl[fs->fs_frag],
 567                         (1 << (allocsiz - 1 + (fs->fs_frag % NBBY))));
 568                 if (loc == 0) {
 569                         errx(1,
 570     "ffs_alloccg: map corrupted: start %d len %d offset %d %ld",
 571                                 ostart, olen,
 572                                 ufs_rw32(cgp->cg_freeoff, needswap),
 573                                 (long)cg_blksfree(cgp, needswap) - (long)cgp);
 574                         /* NOTREACHED */
 575                 }
 576         }
 577         bno = (start + len - loc) * NBBY;
 578         cgp->cg_frotor = ufs_rw32(bno, needswap);
 579         /*
 580          * found the byte in the map
 581          * sift through the bits to find the selected frag
 582          */
 583         for (i = bno + NBBY; bno < i; bno += fs->fs_frag) {
 584                 blk = blkmap(fs, cg_blksfree(cgp, needswap), bno);
 585                 blk <<= 1;
 586                 field = around[allocsiz];
 587                 subfield = inside[allocsiz];
 588                 for (pos = 0; pos <= fs->fs_frag - allocsiz; pos++) {
 589                         if ((blk & field) == subfield)
 590                                 return (bno + pos);
 591                         field <<= 1;
 592                         subfield <<= 1;
 593                 }
 594         }
 595         errx(1, "ffs_alloccg: block not in map: bno %lld", (long long)bno);
 596         return (-1);
 597 }