lib/libfsid/msdosfs.c

   1 /*
   2  * Copyright (c) 2010 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Alex Hornung <ahornung@gmail.com
   6  * and Ákos Kovács <akoskovacs@gmx.com>
   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
  36 #include "libfsid.h"
  37
  38 #include <vfs/msdosfs/bootsect.h>
  39
  40 #define MSDOS_BOOT_BLOCK_SIZE 512
  41
  42 static char *get_volname(char *buf);
  43 static char buffer[MSDOS_BOOT_BLOCK_SIZE * 4];
  44
  45 fsid_t
  46 msdosfs_probe(const char *dev)
  47 {
  48         if (fsid_dev_read(dev, 0L, sizeof(buffer), buffer) != 0)
  49                 return FSID_UNKNOWN;
  50
  51         if (get_volname(buffer) != NULL)
  52                 return FSID_MSDOSFS;
  53
  54         return FSID_MSDOSFS;
  55 }
  56 char *
  57 msdosfs_volname(const char *dev)
  58 {
  59         char *volname;
  60
  61         if (fsid_dev_read(dev, 0L, sizeof(buffer), buffer) != 0)
  62                 return NULL;
  63
  64         volname = get_volname(buffer);
  65
  66         if (volname == NULL || volname[0] == '\0')
  67                 return NULL;
  68
  69         volname[sizeof(volname) - 1] = '\0';
  70
  71         return volname;
  72 }
  73
  74 /*
  75  * This function used to get the offset address of
  76  * the volume name, of the FAT partition.
  77  * It also checks, that is a real FAT partition.
  78 */
  79 static char *
  80 get_volname(char *buff)
  81 {
  82         struct bootsector710 *bpb7;
  83         struct bootsector50 *bpb4;
  84         struct extboot *extb;
  85
  86         bpb7 = (struct bootsector710 *)buff;
  87         bpb4 = (struct bootsector50 *)buff;
  88
  89         /*
  90          * First, assume BPB v7
  91          */
  92         extb = (struct extboot *)bpb7->bsExt;
  93         if ((extb->exBootSignature == 0x28 || extb->exBootSignature == 0x29) &&
  94             strncmp(extb->exFileSysType, "FAT", 3) == 0)
  95                 return extb->exVolumeLabel;
  96
  97         /*
  98          * If this is not a BPB v7, try it as a bpb v4.
  99          */
 100         extb = (struct extboot *)bpb4->bsExt;
 101         if ((extb->exBootSignature == EXBOOTSIG ||
 102              extb->exBootSignature == EXBOOTSIG2) &&
 103             strncmp(extb->exFileSysType, "FAT", 3) == 0)
 104                 return extb->exVolumeLabel;
 105
 106         /*
 107          * If previous checks failed, it may not a FAT filesystem, or
 108          * it may an older one without a volume name.
 109          */
 110         return NULL;
 111 }