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/kernel.h>
   51 #include <sys/lock.h>
   52 #include <sys/malloc.h>
   53 #include <sys/mount.h>
   54 
   55 #include <fs/msdosfs/bpb.h>
   56 #include <fs/msdosfs/direntry.h>
   57 #include <fs/msdosfs/msdosfsmount.h>
   58 
   59 static MALLOC_DEFINE(M_MSDOSFSFILENO, "msdosfs_fileno", "MSDOSFS fileno mapping node");
   60 
   61 RB_PROTOTYPE(msdosfs_filenotree, msdosfs_fileno, mf_tree,
   62     msdosfs_fileno_compare)
   63 
   64 static int msdosfs_fileno_compare(struct msdosfs_fileno *,
   65     struct msdosfs_fileno *);
   66 
   67 #define FILENO_FIRST_DYN        0xf0000000
   68 
   69 /* Initialize file number mapping structures. */
   70 void
   71 msdosfs_fileno_init(struct mount *mp)
   72 {
   73         struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
   74 
   75         RB_INIT(&pmp->pm_filenos);
   76         pmp->pm_nfileno = FILENO_FIRST_DYN;
   77         if (pmp->pm_HugeSectors > 0xffffffff /
   78             (pmp->pm_BytesPerSec / sizeof(struct direntry)) + 1)
   79                 pmp->pm_flags |= MSDOSFS_LARGEFS;
   80 }
   81 
   82 /* Free 32-bit file number generation structures. */
   83 void
   84 msdosfs_fileno_free(struct mount *mp)
   85 {
   86         struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
   87         struct msdosfs_fileno *mf, *next;
   88 
   89         for (mf = RB_MIN(msdosfs_filenotree, &pmp->pm_filenos); mf != NULL;
   90             mf = next) {
   91                 next = RB_NEXT(msdosfs_filenotree, &pmp->pm_filenos, mf);
   92                 RB_REMOVE(msdosfs_filenotree, &pmp->pm_filenos, mf);
   93                 free(mf, M_MSDOSFSFILENO);
   94         }
   95 }
   96 
   97 /* Map a 64-bit file number into a 32-bit one. */
   98 uint32_t
   99 msdosfs_fileno_map(struct mount *mp, uint64_t fileno)
  100 {
  101         struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
  102         struct msdosfs_fileno key, *mf, *tmf;
  103         uint32_t mapped;
  104 
  105         if ((pmp->pm_flags & MSDOSFS_LARGEFS) == 0) {
  106                 KASSERT((uint32_t)fileno == fileno,
  107                     ("fileno >32 bits but not a large fs?"));
  108                 return ((uint32_t)fileno);
  109         }
  110         if (fileno < FILENO_FIRST_DYN)
  111                 return ((uint32_t)fileno);
  112         MSDOSFS_LOCK_MP(pmp);
  113         key.mf_fileno64 = fileno;
  114         mf = RB_FIND(msdosfs_filenotree, &pmp->pm_filenos, &key);
  115         if (mf != NULL) {
  116                 mapped = mf->mf_fileno32;
  117                 MSDOSFS_UNLOCK_MP(pmp);
  118                 return (mapped);
  119         }
  120         if (pmp->pm_nfileno < FILENO_FIRST_DYN)
  121                 panic("msdosfs_fileno_map: wraparound");
  122         MSDOSFS_UNLOCK_MP(pmp);
  123         mf = malloc(sizeof(*mf), M_MSDOSFSFILENO, M_WAITOK);
  124         MSDOSFS_LOCK_MP(pmp);
  125         tmf = RB_FIND(msdosfs_filenotree, &pmp->pm_filenos, &key);
  126         if (tmf != NULL) {
  127                 mapped = tmf->mf_fileno32;
  128                 MSDOSFS_UNLOCK_MP(pmp);
  129                 free(mf, M_MSDOSFSFILENO);
  130                 return (mapped);
  131         }
  132         mf->mf_fileno64 = fileno;
  133         mapped = mf->mf_fileno32 = pmp->pm_nfileno++;
  134         RB_INSERT(msdosfs_filenotree, &pmp->pm_filenos, mf);
  135         MSDOSFS_UNLOCK_MP(pmp);
  136         return (mapped);
  137 }
  138 
  139 /* Compare by 64-bit file number. */
  140 static int
  141 msdosfs_fileno_compare(struct msdosfs_fileno *fa, struct msdosfs_fileno *fb)
  142 {
  143 
  144         if (fa->mf_fileno64 > fb->mf_fileno64)
  145                 return (1);
  146         else if (fa->mf_fileno64 < fb->mf_fileno64)
  147                 return (-1);
  148         return (0);
  149 }
  150 
  151 RB_GENERATE(msdosfs_filenotree, msdosfs_fileno, mf_tree,
  152     msdosfs_fileno_compare)

Cache object: e3630d39844cd6619d9266e6e74322e5


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