The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/fs/msdosfs/msdosfs_fileno.c

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    1 /*-
    2  * Copyright (c) 2003-2004 Tim J. Robbins.
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  */
   26 /*
   27  * Compress 64-bit file numbers into temporary, unique 32-bit file numbers.
   28  * This is needed because the algorithm we use to calculate these numbers
   29  * generates 64-bit quantities, but struct dirent's d_fileno member and
   30  * struct vnodeattr's va_fileid member only have space for 32 bits.
   31  *
   32  * 32-bit file numbers are generated sequentially, and stored in a
   33  * red-black tree, indexed on 64-bit file number. The mappings do not
   34  * persist across reboots (or unmounts); anything that relies on this
   35  * (e.g. NFS) will not work correctly. This scheme consumes 32 bytes
   36  * of kernel memory per file (on i386), and it may be possible for a user
   37  * to cause a panic by creating millions of tiny files.
   38  *
   39  * As an optimization, we split the file number space between statically
   40  * allocated and dynamically allocated. File numbers less than
   41  * FILENO_FIRST_DYN are left unchanged and do not have any tree nodes
   42  * allocated to them.
   43  */
   44 
   45 #include <sys/cdefs.h>
   46 __FBSDID("$FreeBSD$");
   47 
   48 #include <sys/param.h>
   49 #include <sys/systm.h>
   50 #include <sys/conf.h>
   51 #include <sys/kernel.h>
   52 #include <sys/mount.h>
   53 #include <sys/malloc.h>
   54 #include <sys/lock.h>
   55 #include <sys/mutex.h>
   56 
   57 #include <fs/msdosfs/bpb.h>
   58 #include <fs/msdosfs/bootsect.h>
   59 #include <fs/msdosfs/msdosfsmount.h>
   60 #include <fs/msdosfs/direntry.h>
   61 
   62 static MALLOC_DEFINE(M_MSDOSFSFILENO, "MSDOSFS fileno", "MSDOSFS fileno mapping node");
   63 
   64 static struct mtx fileno_mtx;
   65 MTX_SYSINIT(fileno, &fileno_mtx, "MSDOSFS fileno", MTX_DEF);
   66 
   67 RB_PROTOTYPE(msdosfs_filenotree, msdosfs_fileno, mf_tree,
   68     msdosfs_fileno_compare)
   69 
   70 static int msdosfs_fileno_compare(struct msdosfs_fileno *,
   71     struct msdosfs_fileno *);
   72 
   73 #define FILENO_FIRST_DYN        0xf0000000
   74 
   75 /* Initialize file number mapping structures. */
   76 void
   77 msdosfs_fileno_init(mp)
   78         struct mount *mp;
   79 {
   80         struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
   81 
   82         RB_INIT(&pmp->pm_filenos);
   83         pmp->pm_nfileno = FILENO_FIRST_DYN;
   84         if (pmp->pm_HugeSectors > 0xffffffff /
   85             (pmp->pm_BytesPerSec / sizeof(struct direntry)) + 1)
   86                 pmp->pm_flags |= MSDOSFS_LARGEFS;
   87 }
   88 
   89 /* Free 32-bit file number generation structures. */
   90 void
   91 msdosfs_fileno_free(mp)
   92         struct mount *mp;
   93 {
   94         struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
   95         struct msdosfs_fileno *mf, *next;
   96 
   97         for (mf = RB_MIN(msdosfs_filenotree, &pmp->pm_filenos); mf != NULL;
   98             mf = next) {
   99                 next = RB_NEXT(msdosfs_filenotree, &pmp->pm_filenos, mf);
  100                 RB_REMOVE(msdosfs_filenotree, &pmp->pm_filenos, mf);
  101                 free(mf, M_MSDOSFSFILENO);
  102         }
  103 }
  104 
  105 /* Map a 64-bit file number into a 32-bit one. */
  106 uint32_t
  107 msdosfs_fileno_map(mp, fileno)
  108         struct mount *mp;
  109         uint64_t fileno;
  110 {
  111         struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
  112         struct msdosfs_fileno key, *mf, *tmf;
  113         uint32_t mapped;
  114 
  115         if ((pmp->pm_flags & MSDOSFS_LARGEFS) == 0) {
  116                 KASSERT((uint32_t)fileno == fileno,
  117                     ("fileno >32 bits but not a large fs?"));
  118                 return ((uint32_t)fileno);
  119         }
  120         if (fileno < FILENO_FIRST_DYN)
  121                 return ((uint32_t)fileno);
  122         mtx_lock(&fileno_mtx);
  123         key.mf_fileno64 = fileno;
  124         mf = RB_FIND(msdosfs_filenotree, &pmp->pm_filenos, &key);
  125         if (mf != NULL) {
  126                 mapped = mf->mf_fileno32;
  127                 mtx_unlock(&fileno_mtx);
  128                 return (mapped);
  129         }
  130         if (pmp->pm_nfileno < FILENO_FIRST_DYN)
  131                 panic("msdosfs_fileno_map: wraparound");
  132         mtx_unlock(&fileno_mtx);
  133         mf = malloc(sizeof(*mf), M_MSDOSFSFILENO, M_WAITOK);
  134         mtx_lock(&fileno_mtx);
  135         tmf = RB_FIND(msdosfs_filenotree, &pmp->pm_filenos, &key);
  136         if (tmf != NULL) {
  137                 mapped = tmf->mf_fileno32;
  138                 mtx_unlock(&fileno_mtx);
  139                 free(mf, M_MSDOSFSFILENO);
  140                 return (mapped);
  141         }
  142         mf->mf_fileno64 = fileno;
  143         mapped = mf->mf_fileno32 = pmp->pm_nfileno++;
  144         RB_INSERT(msdosfs_filenotree, &pmp->pm_filenos, mf);
  145         mtx_unlock(&fileno_mtx);
  146         return (mapped);
  147 }
  148 
  149 /* Compare by 64-bit file number. */
  150 static int
  151 msdosfs_fileno_compare(fa, fb)
  152         struct msdosfs_fileno *fa, *fb;
  153 {
  154 
  155         if (fa->mf_fileno64 > fb->mf_fileno64)
  156                 return (1);
  157         else if (fa->mf_fileno64 < fb->mf_fileno64)
  158                 return (-1);
  159         return (0);
  160 }
  161 
  162 RB_GENERATE(msdosfs_filenotree, msdosfs_fileno, mf_tree,
  163     msdosfs_fileno_compare)

Cache object: 74bc4bbd9f5efbdaae736c8c897cd3fc


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