The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/fs/msdosfs/msdosfs_fat.c

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    1 /* $FreeBSD$ */
    2 /*      $NetBSD: msdosfs_fat.c,v 1.28 1997/11/17 15:36:49 ws Exp $      */
    3 
    4 /*-
    5  * Copyright (C) 1994, 1995, 1997 Wolfgang Solfrank.
    6  * Copyright (C) 1994, 1995, 1997 TooLs GmbH.
    7  * All rights reserved.
    8  * Original code by Paul Popelka (paulp@uts.amdahl.com) (see below).
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 3. All advertising materials mentioning features or use of this software
   19  *    must display the following acknowledgement:
   20  *      This product includes software developed by TooLs GmbH.
   21  * 4. The name of TooLs GmbH may not be used to endorse or promote products
   22  *    derived from this software without specific prior written permission.
   23  *
   24  * THIS SOFTWARE IS PROVIDED BY TOOLS GMBH ``AS IS'' AND ANY EXPRESS OR
   25  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   26  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   27  * IN NO EVENT SHALL TOOLS GMBH BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   28  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   29  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
   30  * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
   31  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
   32  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   33  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   34  */
   35 /*-
   36  * Written by Paul Popelka (paulp@uts.amdahl.com)
   37  *
   38  * You can do anything you want with this software, just don't say you wrote
   39  * it, and don't remove this notice.
   40  *
   41  * This software is provided "as is".
   42  *
   43  * The author supplies this software to be publicly redistributed on the
   44  * understanding that the author is not responsible for the correct
   45  * functioning of this software in any circumstances and is not liable for
   46  * any damages caused by this software.
   47  *
   48  * October 1992
   49  */
   50 
   51 /*
   52  * kernel include files.
   53  */
   54 #include <sys/param.h>
   55 #include <sys/systm.h>
   56 #include <sys/bio.h>
   57 #include <sys/buf.h>
   58 #include <sys/mount.h>          /* to define statfs structure */
   59 #include <sys/vnode.h>          /* to define vattr structure */
   60 
   61 /*
   62  * msdosfs include files.
   63  */
   64 #include <fs/msdosfs/bpb.h>
   65 #include <fs/msdosfs/msdosfsmount.h>
   66 #include <fs/msdosfs/direntry.h>
   67 #include <fs/msdosfs/denode.h>
   68 #include <fs/msdosfs/fat.h>
   69 
   70 /*
   71  * Fat cache stats.
   72  */
   73 static int fc_fileextends;      /* # of file extends                     */
   74 static int fc_lfcempty;         /* # of time last file cluster cache entry
   75                                  * was empty */
   76 static int fc_bmapcalls;                /* # of times pcbmap was called          */
   77 
   78 #define LMMAX   20
   79 static int fc_lmdistance[LMMAX];/* counters for how far off the last
   80                                  * cluster mapped entry was. */
   81 static int fc_largedistance;    /* off by more than LMMAX                */
   82 static int fc_wherefrom, fc_whereto, fc_lastclust;
   83 static int pm_fatblocksize;
   84 
   85 static int      chainalloc(struct msdosfsmount *pmp, u_long start,
   86                     u_long count, u_long fillwith, u_long *retcluster,
   87                     u_long *got);
   88 static int      chainlength(struct msdosfsmount *pmp, u_long start,
   89                     u_long count);
   90 static void     fatblock(struct msdosfsmount *pmp, u_long ofs, u_long *bnp,
   91                     u_long *sizep, u_long *bop);
   92 static int      fatchain(struct msdosfsmount *pmp, u_long start, u_long count,
   93                     u_long fillwith);
   94 static void     fc_lookup(struct denode *dep, u_long findcn, u_long *frcnp,
   95                     u_long *fsrcnp);
   96 static void     updatefats(struct msdosfsmount *pmp, struct buf *bp,
   97                     u_long fatbn);
   98 static __inline void
   99                 usemap_alloc(struct msdosfsmount *pmp, u_long cn);
  100 static __inline void
  101                 usemap_free(struct msdosfsmount *pmp, u_long cn);
  102 
  103 static void
  104 fatblock(pmp, ofs, bnp, sizep, bop)
  105         struct msdosfsmount *pmp;
  106         u_long ofs;
  107         u_long *bnp;
  108         u_long *sizep;
  109         u_long *bop;
  110 {
  111         u_long bn, size;
  112 
  113         bn = ofs / pmp->pm_fatblocksize * pmp->pm_fatblocksec;
  114         size = min(pmp->pm_fatblocksec, pmp->pm_FATsecs - bn)
  115             * DEV_BSIZE;
  116         bn += pmp->pm_fatblk + pmp->pm_curfat * pmp->pm_FATsecs;
  117 
  118         if (bnp)
  119                 *bnp = bn;
  120         if (sizep)
  121                 *sizep = size;
  122         if (bop)
  123                 *bop = ofs % pmp->pm_fatblocksize;
  124                 pm_fatblocksize = pmp->pm_fatblocksize;
  125 }
  126 
  127 /*
  128  * Map the logical cluster number of a file into a physical disk sector
  129  * that is filesystem relative.
  130  *
  131  * dep    - address of denode representing the file of interest
  132  * findcn - file relative cluster whose filesystem relative cluster number
  133  *          and/or block number are/is to be found
  134  * bnp    - address of where to place the filesystem relative block number.
  135  *          If this pointer is null then don't return this quantity.
  136  * cnp    - address of where to place the filesystem relative cluster number.
  137  *          If this pointer is null then don't return this quantity.
  138  *
  139  * NOTE: Either bnp or cnp must be non-null.
  140  * This function has one side effect.  If the requested file relative cluster
  141  * is beyond the end of file, then the actual number of clusters in the file
  142  * is returned in *cnp.  This is useful for determining how long a directory is.
  143  *  If cnp is null, nothing is returned.
  144  */
  145 int
  146 pcbmap(dep, findcn, bnp, cnp, sp)
  147         struct denode *dep;
  148         u_long findcn;          /* file relative cluster to get          */
  149         daddr_t *bnp;           /* returned filesys relative blk number  */
  150         u_long *cnp;            /* returned cluster number               */
  151         int *sp;                /* returned block size                   */
  152 {
  153         int error;
  154         u_long i;
  155         u_long cn;
  156         u_long prevcn = 0; /* XXX: prevcn could be used unititialized */
  157         u_long byteoffset;
  158         u_long bn;
  159         u_long bo;
  160         struct buf *bp = NULL;
  161         u_long bp_bn = -1;
  162         struct msdosfsmount *pmp = dep->de_pmp;
  163         u_long bsize;
  164 
  165         fc_bmapcalls++;
  166 
  167         /*
  168          * If they don't give us someplace to return a value then don't
  169          * bother doing anything.
  170          */
  171         if (bnp == NULL && cnp == NULL && sp == NULL)
  172                 return (0);
  173 
  174         cn = dep->de_StartCluster;
  175         /*
  176          * The "file" that makes up the root directory is contiguous,
  177          * permanently allocated, of fixed size, and is not made up of
  178          * clusters.  If the cluster number is beyond the end of the root
  179          * directory, then return the number of clusters in the file.
  180          */
  181         if (cn == MSDOSFSROOT) {
  182                 if (dep->de_Attributes & ATTR_DIRECTORY) {
  183                         if (de_cn2off(pmp, findcn) >= dep->de_FileSize) {
  184                                 if (cnp)
  185                                         *cnp = de_bn2cn(pmp, pmp->pm_rootdirsize);
  186                                 return (E2BIG);
  187                         }
  188                         if (bnp)
  189                                 *bnp = pmp->pm_rootdirblk + de_cn2bn(pmp, findcn);
  190                         if (cnp)
  191                                 *cnp = MSDOSFSROOT;
  192                         if (sp)
  193                                 *sp = min(pmp->pm_bpcluster,
  194                                     dep->de_FileSize - de_cn2off(pmp, findcn));
  195                         return (0);
  196                 } else {                /* just an empty file */
  197                         if (cnp)
  198                                 *cnp = 0;
  199                         return (E2BIG);
  200                 }
  201         }
  202 
  203         /*
  204          * All other files do I/O in cluster sized blocks
  205          */
  206         if (sp)
  207                 *sp = pmp->pm_bpcluster;
  208 
  209         /*
  210          * Rummage around in the fat cache, maybe we can avoid tromping
  211          * thru every fat entry for the file. And, keep track of how far
  212          * off the cache was from where we wanted to be.
  213          */
  214         i = 0;
  215         fc_lookup(dep, findcn, &i, &cn);
  216         if ((bn = findcn - i) >= LMMAX) {
  217                 fc_largedistance++;
  218                 fc_wherefrom = i;
  219                 fc_whereto = findcn;
  220                 fc_lastclust = dep->de_fc[FC_LASTFC].fc_frcn;
  221         } else
  222                 fc_lmdistance[bn]++;
  223 
  224         /*
  225          * Handle all other files or directories the normal way.
  226          */
  227         for (; i < findcn; i++) {
  228                 /*
  229                  * Stop with all reserved clusters, not just with EOF.
  230                  */
  231                 if ((cn | ~pmp->pm_fatmask) >= CLUST_RSRVD)
  232                         goto hiteof;
  233                 byteoffset = FATOFS(pmp, cn);
  234                 fatblock(pmp, byteoffset, &bn, &bsize, &bo);
  235                 if (bn != bp_bn) {
  236                         if (bp)
  237                                 brelse(bp);
  238                         error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp);
  239                         if (error) {
  240                                 brelse(bp);
  241                                 return (error);
  242                         }
  243                         bp_bn = bn;
  244                 }
  245                 prevcn = cn;
  246                 if (bo >= bsize) {
  247                         if (bp)
  248                                 brelse(bp);
  249                         return (EIO);
  250                 }
  251                 if (FAT32(pmp))
  252                         cn = getulong(&bp->b_data[bo]);
  253                 else
  254                         cn = getushort(&bp->b_data[bo]);
  255                 if (FAT12(pmp) && (prevcn & 1))
  256                         cn >>= 4;
  257                 cn &= pmp->pm_fatmask;
  258 
  259                 /*
  260                  * Force the special cluster numbers
  261                  * to be the same for all cluster sizes
  262                  * to let the rest of msdosfs handle
  263                  * all cases the same.
  264                  */
  265                 if ((cn | ~pmp->pm_fatmask) >= CLUST_RSRVD)
  266                         cn |= ~pmp->pm_fatmask;
  267         }
  268 
  269         if (!MSDOSFSEOF(pmp, cn)) {
  270                 if (bp)
  271                         brelse(bp);
  272                 if (bnp)
  273                         *bnp = cntobn(pmp, cn);
  274                 if (cnp)
  275                         *cnp = cn;
  276                 fc_setcache(dep, FC_LASTMAP, i, cn);
  277                 return (0);
  278         }
  279 
  280 hiteof:;
  281         if (cnp)
  282                 *cnp = i;
  283         if (bp)
  284                 brelse(bp);
  285         /* update last file cluster entry in the fat cache */
  286         fc_setcache(dep, FC_LASTFC, i - 1, prevcn);
  287         return (E2BIG);
  288 }
  289 
  290 /*
  291  * Find the closest entry in the fat cache to the cluster we are looking
  292  * for.
  293  */
  294 static void
  295 fc_lookup(dep, findcn, frcnp, fsrcnp)
  296         struct denode *dep;
  297         u_long findcn;
  298         u_long *frcnp;
  299         u_long *fsrcnp;
  300 {
  301         int i;
  302         u_long cn;
  303         struct fatcache *closest = 0;
  304 
  305         for (i = 0; i < FC_SIZE; i++) {
  306                 cn = dep->de_fc[i].fc_frcn;
  307                 if (cn != FCE_EMPTY && cn <= findcn) {
  308                         if (closest == 0 || cn > closest->fc_frcn)
  309                                 closest = &dep->de_fc[i];
  310                 }
  311         }
  312         if (closest) {
  313                 *frcnp = closest->fc_frcn;
  314                 *fsrcnp = closest->fc_fsrcn;
  315         }
  316 }
  317 
  318 /*
  319  * Purge the fat cache in denode dep of all entries relating to file
  320  * relative cluster frcn and beyond.
  321  */
  322 void
  323 fc_purge(dep, frcn)
  324         struct denode *dep;
  325         u_int frcn;
  326 {
  327         int i;
  328         struct fatcache *fcp;
  329 
  330         fcp = dep->de_fc;
  331         for (i = 0; i < FC_SIZE; i++, fcp++) {
  332                 if (fcp->fc_frcn >= frcn)
  333                         fcp->fc_frcn = FCE_EMPTY;
  334         }
  335 }
  336 
  337 /*
  338  * Update the fat.
  339  * If mirroring the fat, update all copies, with the first copy as last.
  340  * Else update only the current fat (ignoring the others).
  341  *
  342  * pmp   - msdosfsmount structure for filesystem to update
  343  * bp    - addr of modified fat block
  344  * fatbn - block number relative to begin of filesystem of the modified fat block.
  345  */
  346 static void
  347 updatefats(pmp, bp, fatbn)
  348         struct msdosfsmount *pmp;
  349         struct buf *bp;
  350         u_long fatbn;
  351 {
  352         int i;
  353         struct buf *bpn;
  354 
  355 #ifdef MSDOSFS_DEBUG
  356         printf("updatefats(pmp %p, bp %p, fatbn %lu)\n", pmp, bp, fatbn);
  357 #endif
  358 
  359         /*
  360          * If we have an FSInfo block, update it.
  361          */
  362         if (pmp->pm_fsinfo) {
  363                 u_long cn = pmp->pm_nxtfree;
  364 
  365                 if (pmp->pm_freeclustercount
  366                     && (pmp->pm_inusemap[cn / N_INUSEBITS]
  367                         & (1 << (cn % N_INUSEBITS)))) {
  368                         /*
  369                          * The cluster indicated in FSInfo isn't free
  370                          * any longer.  Got get a new free one.
  371                          */
  372                         for (cn = 0; cn < pmp->pm_maxcluster; cn += N_INUSEBITS)
  373                                 if (pmp->pm_inusemap[cn / N_INUSEBITS] != (u_int)-1)
  374                                         break;
  375                         pmp->pm_nxtfree = cn
  376                                 + ffs(pmp->pm_inusemap[cn / N_INUSEBITS]
  377                                       ^ (u_int)-1) - 1;
  378                 }
  379                 if (bread(pmp->pm_devvp, pmp->pm_fsinfo, fsi_size(pmp), 
  380                     NOCRED, &bpn) != 0) {
  381                         /*
  382                          * Ignore the error, but turn off FSInfo update for the future.
  383                          */
  384                         pmp->pm_fsinfo = 0;
  385                         brelse(bpn);
  386                 } else {
  387                         struct fsinfo *fp = (struct fsinfo *)bpn->b_data;
  388 
  389                         putulong(fp->fsinfree, pmp->pm_freeclustercount);
  390                         putulong(fp->fsinxtfree, pmp->pm_nxtfree);
  391                         if (pmp->pm_flags & MSDOSFSMNT_WAITONFAT)
  392                                 bwrite(bpn);
  393                         else
  394                                 bdwrite(bpn);
  395                 }
  396         }
  397 
  398         if (pmp->pm_flags & MSDOSFS_FATMIRROR) {
  399                 /*
  400                  * Now copy the block(s) of the modified fat to the other copies of
  401                  * the fat and write them out.  This is faster than reading in the
  402                  * other fats and then writing them back out.  This could tie up
  403                  * the fat for quite a while. Preventing others from accessing it.
  404                  * To prevent us from going after the fat quite so much we use
  405                  * delayed writes, unless they specfied "synchronous" when the
  406                  * filesystem was mounted.  If synch is asked for then use
  407                  * bwrite()'s and really slow things down.
  408                  */
  409                 for (i = 1; i < pmp->pm_FATs; i++) {
  410                         fatbn += pmp->pm_FATsecs;
  411                         /* getblk() never fails */
  412                         bpn = getblk(pmp->pm_devvp, fatbn, bp->b_bcount,
  413                             0, 0, 0);
  414                         bcopy(bp->b_data, bpn->b_data, bp->b_bcount);
  415                         if (pmp->pm_flags & MSDOSFSMNT_WAITONFAT)
  416                                 bwrite(bpn);
  417                         else
  418                                 bdwrite(bpn);
  419                 }
  420         }
  421 
  422         /*
  423          * Write out the first (or current) fat last.
  424          */
  425         if (pmp->pm_flags & MSDOSFSMNT_WAITONFAT)
  426                 bwrite(bp);
  427         else
  428                 bdwrite(bp);
  429         /*
  430          * Maybe update fsinfo sector here?
  431          */
  432 }
  433 
  434 /*
  435  * Updating entries in 12 bit fats is a pain in the butt.
  436  *
  437  * The following picture shows where nibbles go when moving from a 12 bit
  438  * cluster number into the appropriate bytes in the FAT.
  439  *
  440  *      byte m        byte m+1      byte m+2
  441  *      +----+----+   +----+----+   +----+----+
  442  *      |  0    1 |   |  2    3 |   |  4    5 |   FAT bytes
  443  *      +----+----+   +----+----+   +----+----+
  444  *
  445  *      +----+----+----+   +----+----+----+
  446  *      |  3    0    1 |   |  4    5    2 |
  447  *      +----+----+----+   +----+----+----+
  448  *      cluster n          cluster n+1
  449  *
  450  * Where n is even. m = n + (n >> 2)
  451  *
  452  */
  453 static __inline void
  454 usemap_alloc(pmp, cn)
  455         struct msdosfsmount *pmp;
  456         u_long cn;
  457 {
  458 
  459         pmp->pm_inusemap[cn / N_INUSEBITS] |= 1 << (cn % N_INUSEBITS);
  460         pmp->pm_freeclustercount--;
  461 }
  462 
  463 static __inline void
  464 usemap_free(pmp, cn)
  465         struct msdosfsmount *pmp;
  466         u_long cn;
  467 {
  468 
  469         pmp->pm_freeclustercount++;
  470         pmp->pm_inusemap[cn / N_INUSEBITS] &= ~(1 << (cn % N_INUSEBITS));
  471 }
  472 
  473 int
  474 clusterfree(pmp, cluster, oldcnp)
  475         struct msdosfsmount *pmp;
  476         u_long cluster;
  477         u_long *oldcnp;
  478 {
  479         int error;
  480         u_long oldcn;
  481 
  482         usemap_free(pmp, cluster);
  483         error = fatentry(FAT_GET_AND_SET, pmp, cluster, &oldcn, MSDOSFSFREE);
  484         if (error) {
  485                 usemap_alloc(pmp, cluster);
  486                 return (error);
  487         }
  488         /*
  489          * If the cluster was successfully marked free, then update
  490          * the count of free clusters, and turn off the "allocated"
  491          * bit in the "in use" cluster bit map.
  492          */
  493         if (oldcnp)
  494                 *oldcnp = oldcn;
  495         return (0);
  496 }
  497 
  498 /*
  499  * Get or Set or 'Get and Set' the cluster'th entry in the fat.
  500  *
  501  * function     - whether to get or set a fat entry
  502  * pmp          - address of the msdosfsmount structure for the filesystem
  503  *                whose fat is to be manipulated.
  504  * cn           - which cluster is of interest
  505  * oldcontents  - address of a word that is to receive the contents of the
  506  *                cluster'th entry if this is a get function
  507  * newcontents  - the new value to be written into the cluster'th element of
  508  *                the fat if this is a set function.
  509  *
  510  * This function can also be used to free a cluster by setting the fat entry
  511  * for a cluster to 0.
  512  *
  513  * All copies of the fat are updated if this is a set function. NOTE: If
  514  * fatentry() marks a cluster as free it does not update the inusemap in
  515  * the msdosfsmount structure. This is left to the caller.
  516  */
  517 int
  518 fatentry(function, pmp, cn, oldcontents, newcontents)
  519         int function;
  520         struct msdosfsmount *pmp;
  521         u_long cn;
  522         u_long *oldcontents;
  523         u_long newcontents;
  524 {
  525         int error;
  526         u_long readcn;
  527         u_long bn, bo, bsize, byteoffset;
  528         struct buf *bp;
  529 
  530 #ifdef  MSDOSFS_DEBUG
  531         printf("fatentry(func %d, pmp %p, clust %lu, oldcon %p, newcon %lx)\n",
  532              function, pmp, cn, oldcontents, newcontents);
  533 #endif
  534 
  535 #ifdef DIAGNOSTIC
  536         /*
  537          * Be sure they asked us to do something.
  538          */
  539         if ((function & (FAT_SET | FAT_GET)) == 0) {
  540                 printf("fatentry(): function code doesn't specify get or set\n");
  541                 return (EINVAL);
  542         }
  543 
  544         /*
  545          * If they asked us to return a cluster number but didn't tell us
  546          * where to put it, give them an error.
  547          */
  548         if ((function & FAT_GET) && oldcontents == NULL) {
  549                 printf("fatentry(): get function with no place to put result\n");
  550                 return (EINVAL);
  551         }
  552 #endif
  553 
  554         /*
  555          * Be sure the requested cluster is in the filesystem.
  556          */
  557         if (cn < CLUST_FIRST || cn > pmp->pm_maxcluster)
  558                 return (EINVAL);
  559 
  560         byteoffset = FATOFS(pmp, cn);
  561         fatblock(pmp, byteoffset, &bn, &bsize, &bo);
  562         error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp);
  563         if (error) {
  564                 brelse(bp);
  565                 return (error);
  566         }
  567 
  568         if (function & FAT_GET) {
  569                 if (FAT32(pmp))
  570                         readcn = getulong(&bp->b_data[bo]);
  571                 else
  572                         readcn = getushort(&bp->b_data[bo]);
  573                 if (FAT12(pmp) & (cn & 1))
  574                         readcn >>= 4;
  575                 readcn &= pmp->pm_fatmask;
  576                 /* map reserved fat entries to same values for all fats */
  577                 if ((readcn | ~pmp->pm_fatmask) >= CLUST_RSRVD)
  578                         readcn |= ~pmp->pm_fatmask;
  579                 *oldcontents = readcn;
  580         }
  581         if (function & FAT_SET) {
  582                 switch (pmp->pm_fatmask) {
  583                 case FAT12_MASK:
  584                         readcn = getushort(&bp->b_data[bo]);
  585                         if (cn & 1) {
  586                                 readcn &= 0x000f;
  587                                 readcn |= newcontents << 4;
  588                         } else {
  589                                 readcn &= 0xf000;
  590                                 readcn |= newcontents & 0xfff;
  591                         }
  592                         putushort(&bp->b_data[bo], readcn);
  593                         break;
  594                 case FAT16_MASK:
  595                         putushort(&bp->b_data[bo], newcontents);
  596                         break;
  597                 case FAT32_MASK:
  598                         /*
  599                          * According to spec we have to retain the
  600                          * high order bits of the fat entry.
  601                          */
  602                         readcn = getulong(&bp->b_data[bo]);
  603                         readcn &= ~FAT32_MASK;
  604                         readcn |= newcontents & FAT32_MASK;
  605                         putulong(&bp->b_data[bo], readcn);
  606                         break;
  607                 }
  608                 updatefats(pmp, bp, bn);
  609                 bp = NULL;
  610                 pmp->pm_fmod = 1;
  611         }
  612         if (bp)
  613                 brelse(bp);
  614         return (0);
  615 }
  616 
  617 /*
  618  * Update a contiguous cluster chain
  619  *
  620  * pmp      - mount point
  621  * start    - first cluster of chain
  622  * count    - number of clusters in chain
  623  * fillwith - what to write into fat entry of last cluster
  624  */
  625 static int
  626 fatchain(pmp, start, count, fillwith)
  627         struct msdosfsmount *pmp;
  628         u_long start;
  629         u_long count;
  630         u_long fillwith;
  631 {
  632         int error;
  633         u_long bn, bo, bsize, byteoffset, readcn, newc;
  634         struct buf *bp;
  635 
  636 #ifdef MSDOSFS_DEBUG
  637         printf("fatchain(pmp %p, start %lu, count %lu, fillwith %lx)\n",
  638             pmp, start, count, fillwith);
  639 #endif
  640         /*
  641          * Be sure the clusters are in the filesystem.
  642          */
  643         if (start < CLUST_FIRST || start + count - 1 > pmp->pm_maxcluster)
  644                 return (EINVAL);
  645 
  646         while (count > 0) {
  647                 byteoffset = FATOFS(pmp, start);
  648                 fatblock(pmp, byteoffset, &bn, &bsize, &bo);
  649                 error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp);
  650                 if (error) {
  651                         brelse(bp);
  652                         return (error);
  653                 }
  654                 while (count > 0) {
  655                         start++;
  656                         newc = --count > 0 ? start : fillwith;
  657                         switch (pmp->pm_fatmask) {
  658                         case FAT12_MASK:
  659                                 readcn = getushort(&bp->b_data[bo]);
  660                                 if (start & 1) {
  661                                         readcn &= 0xf000;
  662                                         readcn |= newc & 0xfff;
  663                                 } else {
  664                                         readcn &= 0x000f;
  665                                         readcn |= newc << 4;
  666                                 }
  667                                 putushort(&bp->b_data[bo], readcn);
  668                                 bo++;
  669                                 if (!(start & 1))
  670                                         bo++;
  671                                 break;
  672                         case FAT16_MASK:
  673                                 putushort(&bp->b_data[bo], newc);
  674                                 bo += 2;
  675                                 break;
  676                         case FAT32_MASK:
  677                                 readcn = getulong(&bp->b_data[bo]);
  678                                 readcn &= ~pmp->pm_fatmask;
  679                                 readcn |= newc & pmp->pm_fatmask;
  680                                 putulong(&bp->b_data[bo], readcn);
  681                                 bo += 4;
  682                                 break;
  683                         }
  684                         if (bo >= bsize)
  685                                 break;
  686                 }
  687                 updatefats(pmp, bp, bn);
  688         }
  689         pmp->pm_fmod = 1;
  690         return (0);
  691 }
  692 
  693 /*
  694  * Check the length of a free cluster chain starting at start.
  695  *
  696  * pmp   - mount point
  697  * start - start of chain
  698  * count - maximum interesting length
  699  */
  700 static int
  701 chainlength(pmp, start, count)
  702         struct msdosfsmount *pmp;
  703         u_long start;
  704         u_long count;
  705 {
  706         u_long idx, max_idx;
  707         u_int map;
  708         u_long len;
  709 
  710         max_idx = pmp->pm_maxcluster / N_INUSEBITS;
  711         idx = start / N_INUSEBITS;
  712         start %= N_INUSEBITS;
  713         map = pmp->pm_inusemap[idx];
  714         map &= ~((1 << start) - 1);
  715         if (map) {
  716                 len = ffs(map) - 1 - start;
  717                 return (len > count ? count : len);
  718         }
  719         len = N_INUSEBITS - start;
  720         if (len >= count)
  721                 return (count);
  722         while (++idx <= max_idx) {
  723                 if (len >= count)
  724                         break;
  725                 map = pmp->pm_inusemap[idx];
  726                 if (map) {
  727                         len +=  ffs(map) - 1;
  728                         break;
  729                 }
  730                 len += N_INUSEBITS;
  731         }
  732         return (len > count ? count : len);
  733 }
  734 
  735 /*
  736  * Allocate contigous free clusters.
  737  *
  738  * pmp        - mount point.
  739  * start      - start of cluster chain.
  740  * count      - number of clusters to allocate.
  741  * fillwith   - put this value into the fat entry for the
  742  *              last allocated cluster.
  743  * retcluster - put the first allocated cluster's number here.
  744  * got        - how many clusters were actually allocated.
  745  */
  746 static int
  747 chainalloc(pmp, start, count, fillwith, retcluster, got)
  748         struct msdosfsmount *pmp;
  749         u_long start;
  750         u_long count;
  751         u_long fillwith;
  752         u_long *retcluster;
  753         u_long *got;
  754 {
  755         int error;
  756         u_long cl, n;
  757 
  758         for (cl = start, n = count; n-- > 0;)
  759                 usemap_alloc(pmp, cl++);
  760 
  761         error = fatchain(pmp, start, count, fillwith);
  762         if (error != 0)
  763                 return (error);
  764 #ifdef MSDOSFS_DEBUG
  765         printf("clusteralloc(): allocated cluster chain at %lu (%lu clusters)\n",
  766             start, count);
  767 #endif
  768         if (retcluster)
  769                 *retcluster = start;
  770         if (got)
  771                 *got = count;
  772         return (0);
  773 }
  774 
  775 /*
  776  * Allocate contiguous free clusters.
  777  *
  778  * pmp        - mount point.
  779  * start      - preferred start of cluster chain.
  780  * count      - number of clusters requested.
  781  * fillwith   - put this value into the fat entry for the
  782  *              last allocated cluster.
  783  * retcluster - put the first allocated cluster's number here.
  784  * got        - how many clusters were actually allocated.
  785  */
  786 int
  787 clusteralloc(pmp, start, count, fillwith, retcluster, got)
  788         struct msdosfsmount *pmp;
  789         u_long start;
  790         u_long count;
  791         u_long fillwith;
  792         u_long *retcluster;
  793         u_long *got;
  794 {
  795         u_long idx;
  796         u_long len, newst, foundl, cn, l;
  797         u_long foundcn = 0; /* XXX: foundcn could be used unititialized */
  798         u_int map;
  799 
  800 #ifdef MSDOSFS_DEBUG
  801         printf("clusteralloc(): find %lu clusters\n",count);
  802 #endif
  803         if (start) {
  804                 if ((len = chainlength(pmp, start, count)) >= count)
  805                         return (chainalloc(pmp, start, count, fillwith, retcluster, got));
  806         } else 
  807                 len = 0;
  808 
  809         /*
  810          * Start at a (pseudo) random place to maximize cluster runs
  811          * under multiple writers.
  812          */
  813         newst = random() % (pmp->pm_maxcluster + 1);
  814         foundl = 0;
  815 
  816         for (cn = newst; cn <= pmp->pm_maxcluster;) {
  817                 idx = cn / N_INUSEBITS;
  818                 map = pmp->pm_inusemap[idx];
  819                 map |= (1 << (cn % N_INUSEBITS)) - 1;
  820                 if (map != (u_int)-1) {
  821                         cn = idx * N_INUSEBITS + ffs(map^(u_int)-1) - 1;
  822                         if ((l = chainlength(pmp, cn, count)) >= count)
  823                                 return (chainalloc(pmp, cn, count, fillwith, retcluster, got));
  824                         if (l > foundl) {
  825                                 foundcn = cn;
  826                                 foundl = l;
  827                         }
  828                         cn += l + 1;
  829                         continue;
  830                 }
  831                 cn += N_INUSEBITS - cn % N_INUSEBITS;
  832         }
  833         for (cn = 0; cn < newst;) {
  834                 idx = cn / N_INUSEBITS;
  835                 map = pmp->pm_inusemap[idx];
  836                 map |= (1 << (cn % N_INUSEBITS)) - 1;
  837                 if (map != (u_int)-1) {
  838                         cn = idx * N_INUSEBITS + ffs(map^(u_int)-1) - 1;
  839                         if ((l = chainlength(pmp, cn, count)) >= count)
  840                                 return (chainalloc(pmp, cn, count, fillwith, retcluster, got));
  841                         if (l > foundl) {
  842                                 foundcn = cn;
  843                                 foundl = l;
  844                         }
  845                         cn += l + 1;
  846                         continue;
  847                 }
  848                 cn += N_INUSEBITS - cn % N_INUSEBITS;
  849         }
  850 
  851         if (!foundl)
  852                 return (ENOSPC);
  853 
  854         if (len)
  855                 return (chainalloc(pmp, start, len, fillwith, retcluster, got));
  856         else
  857                 return (chainalloc(pmp, foundcn, foundl, fillwith, retcluster, got));
  858 }
  859 
  860 
  861 /*
  862  * Free a chain of clusters.
  863  *
  864  * pmp          - address of the msdosfs mount structure for the filesystem
  865  *                containing the cluster chain to be freed.
  866  * startcluster - number of the 1st cluster in the chain of clusters to be
  867  *                freed.
  868  */
  869 int
  870 freeclusterchain(pmp, cluster)
  871         struct msdosfsmount *pmp;
  872         u_long cluster;
  873 {
  874         int error;
  875         struct buf *bp = NULL;
  876         u_long bn, bo, bsize, byteoffset;
  877         u_long readcn, lbn = -1;
  878 
  879         while (cluster >= CLUST_FIRST && cluster <= pmp->pm_maxcluster) {
  880                 byteoffset = FATOFS(pmp, cluster);
  881                 fatblock(pmp, byteoffset, &bn, &bsize, &bo);
  882                 if (lbn != bn) {
  883                         if (bp)
  884                                 updatefats(pmp, bp, lbn);
  885                         error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp);
  886                         if (error) {
  887                                 brelse(bp);
  888                                 return (error);
  889                         }
  890                         lbn = bn;
  891                 }
  892                 usemap_free(pmp, cluster);
  893                 switch (pmp->pm_fatmask) {
  894                 case FAT12_MASK:
  895                         readcn = getushort(&bp->b_data[bo]);
  896                         if (cluster & 1) {
  897                                 cluster = readcn >> 4;
  898                                 readcn &= 0x000f;
  899                                 readcn |= MSDOSFSFREE << 4;
  900                         } else {
  901                                 cluster = readcn;
  902                                 readcn &= 0xf000;
  903                                 readcn |= MSDOSFSFREE & 0xfff;
  904                         }
  905                         putushort(&bp->b_data[bo], readcn);
  906                         break;
  907                 case FAT16_MASK:
  908                         cluster = getushort(&bp->b_data[bo]);
  909                         putushort(&bp->b_data[bo], MSDOSFSFREE);
  910                         break;
  911                 case FAT32_MASK:
  912                         cluster = getulong(&bp->b_data[bo]);
  913                         putulong(&bp->b_data[bo],
  914                                  (MSDOSFSFREE & FAT32_MASK) | (cluster & ~FAT32_MASK));
  915                         break;
  916                 }
  917                 cluster &= pmp->pm_fatmask;
  918                 if ((cluster | ~pmp->pm_fatmask) >= CLUST_RSRVD)
  919                         cluster |= pmp->pm_fatmask;
  920         }
  921         if (bp)
  922                 updatefats(pmp, bp, bn);
  923         return (0);
  924 }
  925 
  926 /*
  927  * Read in fat blocks looking for free clusters. For every free cluster
  928  * found turn off its corresponding bit in the pm_inusemap.
  929  */
  930 int
  931 fillinusemap(pmp)
  932         struct msdosfsmount *pmp;
  933 {
  934         struct buf *bp = NULL;
  935         u_long cn, readcn;
  936         int error;
  937         u_long bn, bo, bsize, byteoffset;
  938 
  939         /*
  940          * Mark all clusters in use, we mark the free ones in the fat scan
  941          * loop further down.
  942          */
  943         for (cn = 0; cn < (pmp->pm_maxcluster + N_INUSEBITS) / N_INUSEBITS; cn++)
  944                 pmp->pm_inusemap[cn] = (u_int)-1;
  945 
  946         /*
  947          * Figure how many free clusters are in the filesystem by ripping
  948          * through the fat counting the number of entries whose content is
  949          * zero.  These represent free clusters.
  950          */
  951         pmp->pm_freeclustercount = 0;
  952         for (cn = CLUST_FIRST; cn <= pmp->pm_maxcluster; cn++) {
  953                 byteoffset = FATOFS(pmp, cn);
  954                 bo = byteoffset % pmp->pm_fatblocksize;
  955                 if (!bo || !bp) {
  956                         /* Read new FAT block */
  957                         if (bp)
  958                                 brelse(bp);
  959                         fatblock(pmp, byteoffset, &bn, &bsize, NULL);
  960                         error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp);
  961                         if (error) {
  962                                 brelse(bp);
  963                                 return (error);
  964                         }
  965                 }
  966                 if (FAT32(pmp))
  967                         readcn = getulong(&bp->b_data[bo]);
  968                 else
  969                         readcn = getushort(&bp->b_data[bo]);
  970                 if (FAT12(pmp) && (cn & 1))
  971                         readcn >>= 4;
  972                 readcn &= pmp->pm_fatmask;
  973 
  974                 if (readcn == 0)
  975                         usemap_free(pmp, cn);
  976         }
  977         brelse(bp);
  978         return (0);
  979 }
  980 
  981 /*
  982  * Allocate a new cluster and chain it onto the end of the file.
  983  *
  984  * dep   - the file to extend
  985  * count - number of clusters to allocate
  986  * bpp   - where to return the address of the buf header for the first new
  987  *         file block
  988  * ncp   - where to put cluster number of the first newly allocated cluster
  989  *         If this pointer is 0, do not return the cluster number.
  990  * flags - see fat.h
  991  *
  992  * NOTE: This function is not responsible for turning on the DE_UPDATE bit of
  993  * the de_flag field of the denode and it does not change the de_FileSize
  994  * field.  This is left for the caller to do.
  995  */
  996 int
  997 extendfile(dep, count, bpp, ncp, flags)
  998         struct denode *dep;
  999         u_long count;
 1000         struct buf **bpp;
 1001         u_long *ncp;
 1002         int flags;
 1003 {
 1004         int error;
 1005         u_long frcn;
 1006         u_long cn, got;
 1007         struct msdosfsmount *pmp = dep->de_pmp;
 1008         struct buf *bp;
 1009         daddr_t blkno;
 1010 
 1011         /*
 1012          * Don't try to extend the root directory
 1013          */
 1014         if (dep->de_StartCluster == MSDOSFSROOT
 1015             && (dep->de_Attributes & ATTR_DIRECTORY)) {
 1016                 printf("extendfile(): attempt to extend root directory\n");
 1017                 return (ENOSPC);
 1018         }
 1019 
 1020         /*
 1021          * If the "file's last cluster" cache entry is empty, and the file
 1022          * is not empty, then fill the cache entry by calling pcbmap().
 1023          */
 1024         fc_fileextends++;
 1025         if (dep->de_fc[FC_LASTFC].fc_frcn == FCE_EMPTY &&
 1026             dep->de_StartCluster != 0) {
 1027                 fc_lfcempty++;
 1028                 error = pcbmap(dep, 0xffff, 0, &cn, 0);
 1029                 /* we expect it to return E2BIG */
 1030                 if (error != E2BIG)
 1031                         return (error);
 1032         }
 1033 
 1034         fc_last_to_nexttolast(dep);
 1035 
 1036         while (count > 0) {
 1037                 /*
 1038                  * Allocate a new cluster chain and cat onto the end of the
 1039                  * file.  * If the file is empty we make de_StartCluster point
 1040                  * to the new block.  Note that de_StartCluster being 0 is
 1041                  * sufficient to be sure the file is empty since we exclude
 1042                  * attempts to extend the root directory above, and the root
 1043                  * dir is the only file with a startcluster of 0 that has
 1044                  * blocks allocated (sort of).
 1045                  */
 1046                 if (dep->de_StartCluster == 0)
 1047                         cn = 0;
 1048                 else
 1049                         cn = dep->de_fc[FC_LASTFC].fc_fsrcn + 1;
 1050                 error = clusteralloc(pmp, cn, count, CLUST_EOFE, &cn, &got);
 1051                 if (error)
 1052                         return (error);
 1053 
 1054                 count -= got;
 1055 
 1056                 /*
 1057                  * Give them the filesystem relative cluster number if they want
 1058                  * it.
 1059                  */
 1060                 if (ncp) {
 1061                         *ncp = cn;
 1062                         ncp = NULL;
 1063                 }
 1064 
 1065                 if (dep->de_StartCluster == 0) {
 1066                         dep->de_StartCluster = cn;
 1067                         frcn = 0;
 1068                 } else {
 1069                         error = fatentry(FAT_SET, pmp,
 1070                                          dep->de_fc[FC_LASTFC].fc_fsrcn,
 1071                                          0, cn);
 1072                         if (error) {
 1073                                 clusterfree(pmp, cn, NULL);
 1074                                 return (error);
 1075                         }
 1076                         frcn = dep->de_fc[FC_LASTFC].fc_frcn + 1;
 1077                 }
 1078 
 1079                 /*
 1080                  * Update the "last cluster of the file" entry in the denode's fat
 1081                  * cache.
 1082                  */
 1083                 fc_setcache(dep, FC_LASTFC, frcn + got - 1, cn + got - 1);
 1084 
 1085                 if (flags & DE_CLEAR) {
 1086                         while (got-- > 0) {
 1087                                 /*
 1088                                  * Get the buf header for the new block of the file.
 1089                                  */
 1090                                 if (dep->de_Attributes & ATTR_DIRECTORY)
 1091                                         bp = getblk(pmp->pm_devvp,
 1092                                                     cntobn(pmp, cn++),
 1093                                                     pmp->pm_bpcluster, 0, 0, 0);
 1094                                 else {
 1095                                         bp = getblk(DETOV(dep),
 1096                                             frcn++,
 1097                                             pmp->pm_bpcluster, 0, 0, 0);
 1098                                         /*
 1099                                          * Do the bmap now, as in msdosfs_write
 1100                                          */
 1101                                         if (pcbmap(dep,
 1102                                             bp->b_lblkno,
 1103                                             &blkno, 0, 0))
 1104                                                 bp->b_blkno = -1;
 1105                                         if (bp->b_blkno == -1)
 1106                                                 panic("extendfile: pcbmap");
 1107                                         else
 1108                                                 bp->b_blkno = blkno;
 1109                                 }
 1110                                 clrbuf(bp);
 1111                                 if (bpp) {
 1112                                         *bpp = bp;
 1113                                         bpp = NULL;
 1114                                 } else
 1115                                         bdwrite(bp);
 1116                         }
 1117                 }
 1118         }
 1119 
 1120         return (0);
 1121 }
 1122 
 1123 /*-
 1124  * Routine to mark a FAT16 or FAT32 volume as "clean" or "dirty" by
 1125  * manipulating the upper bit of the FAT entry for cluster 1.  Note that
 1126  * this bit is not defined for FAT12 volumes, which are always assumed to
 1127  * be dirty.
 1128  *
 1129  * The fatentry() routine only works on cluster numbers that a file could
 1130  * occupy, so it won't manipulate the entry for cluster 1.  So we have to do
 1131  * it here.  The code was stolen from fatentry() and tailored for cluster 1.
 1132  *
 1133  * Inputs:
 1134  *      pmp     The MS-DOS volume to mark
 1135  *      dirty   Non-zero if the volume should be marked dirty; zero if it
 1136  *              should be marked clean
 1137  *
 1138  * Result:
 1139  *      0       Success
 1140  *      EROFS   Volume is read-only
 1141  *      ?       (other errors from called routines)
 1142  */
 1143 int
 1144 markvoldirty(struct msdosfsmount *pmp, int dirty)
 1145 {
 1146         struct buf *bp;
 1147         u_long bn, bo, bsize, byteoffset, fatval;
 1148         int error;
 1149 
 1150         /*
 1151          * FAT12 does not support a "clean" bit, so don't do anything for
 1152          * FAT12.
 1153          */
 1154         if (FAT12(pmp))
 1155                 return (0);
 1156 
 1157         /* Can't change the bit on a read-only filesystem. */
 1158         if (pmp->pm_flags & MSDOSFSMNT_RONLY)
 1159                 return (EROFS);
 1160 
 1161         /*
 1162          * Fetch the block containing the FAT entry.  It is given by the
 1163          * pseudo-cluster 1.
 1164          */
 1165         byteoffset = FATOFS(pmp, 1);
 1166         fatblock(pmp, byteoffset, &bn, &bsize, &bo);
 1167         error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp);
 1168         if (error) {
 1169                 brelse(bp);
 1170                 return (error);
 1171         }
 1172 
 1173         /*
 1174          * Get the current value of the FAT entry and set/clear the relevant
 1175          * bit.  Dirty means clear the "clean" bit; clean means set the
 1176          * "clean" bit.
 1177          */
 1178         if (FAT32(pmp)) {
 1179                 /* FAT32 uses bit 27. */
 1180                 fatval = getulong(&bp->b_data[bo]);
 1181                 if (dirty)
 1182                         fatval &= 0xF7FFFFFF;
 1183                 else
 1184                         fatval |= 0x08000000;
 1185                 putulong(&bp->b_data[bo], fatval);
 1186         } else {
 1187                 /* Must be FAT16; use bit 15. */
 1188                 fatval = getushort(&bp->b_data[bo]);
 1189                 if (dirty)
 1190                         fatval &= 0x7FFF;
 1191                 else
 1192                         fatval |= 0x8000;
 1193                 putushort(&bp->b_data[bo], fatval);
 1194         }
 1195 
 1196         /* Write out the modified FAT block synchronously. */
 1197         return (bwrite(bp));
 1198 }

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