| 1 | /* ----------------------------------------------------------------------- * |
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| 2 | * |
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| 3 | * Copyright 2004-2008 H. Peter Anvin - All Rights Reserved |
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| 4 | * |
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| 5 | * This program is free software; you can redistribute it and/or modify |
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| 6 | * it under the terms of the GNU General Public License as published by |
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| 7 | * the Free Software Foundation, Inc., 53 Temple Place Ste 330, |
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| 8 | * Boston MA 02111-1307, USA; either version 2 of the License, or |
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| 9 | * (at your option) any later version; incorporated herein by reference. |
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| 10 | * |
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| 11 | * ----------------------------------------------------------------------- */ |
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| 12 | |
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| 13 | /* |
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| 14 | * fatchain.c |
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| 15 | * |
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| 16 | * Follow a FAT chain |
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| 17 | */ |
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| 18 | |
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| 19 | #include "libfatint.h" |
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| 20 | #include "ulint.h" |
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| 21 | |
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| 22 | /* |
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| 23 | * Convert a cluster number (or 0 for the root directory) to a |
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| 24 | * sector number. Return -1 on failure. |
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| 25 | */ |
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| 26 | libfat_sector_t libfat_clustertosector(const struct libfat_filesystem *fs, |
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| 27 | int32_t cluster) |
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| 28 | { |
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| 29 | if (cluster == 0) |
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| 30 | cluster = fs->rootcluster; |
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| 31 | |
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| 32 | if (cluster == 0) |
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| 33 | return fs->rootdir; |
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| 34 | else if (cluster < 2 || cluster >= fs->endcluster) |
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| 35 | return -1; |
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| 36 | else |
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| 37 | return fs->data + ((libfat_sector_t) (cluster - 2) << fs->clustshift); |
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| 38 | } |
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| 39 | |
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| 40 | /* |
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| 41 | * Get the next sector of either the root directory or a FAT chain. |
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| 42 | * Returns 0 on end of file and -1 on error. |
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| 43 | */ |
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| 44 | |
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| 45 | libfat_sector_t libfat_nextsector(struct libfat_filesystem * fs, |
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| 46 | libfat_sector_t s) |
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| 47 | { |
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| 48 | int32_t cluster, nextcluster; |
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| 49 | uint32_t fatoffset; |
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| 50 | libfat_sector_t fatsect; |
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| 51 | uint8_t *fsdata; |
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| 52 | uint32_t clustmask = fs->clustsize - 1; |
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| 53 | libfat_sector_t rs; |
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| 54 | |
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| 55 | if (s < fs->data) { |
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| 56 | if (s < fs->rootdir) |
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| 57 | return -1; |
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| 58 | |
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| 59 | /* Root directory */ |
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| 60 | s++; |
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| 61 | return (s < fs->data) ? s : 0; |
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| 62 | } |
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| 63 | |
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| 64 | rs = s - fs->data; |
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| 65 | |
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| 66 | if (~rs & clustmask) |
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| 67 | return s + 1; /* Next sector in cluster */ |
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| 68 | |
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| 69 | cluster = 2 + (rs >> fs->clustshift); |
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| 70 | |
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| 71 | if (cluster >= fs->endcluster) |
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| 72 | return -1; |
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| 73 | |
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| 74 | switch (fs->fat_type) { |
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| 75 | case FAT12: |
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| 76 | /* Get first byte */ |
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| 77 | fatoffset = cluster + (cluster >> 1); |
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| 78 | fatsect = fs->fat + (fatoffset >> LIBFAT_SECTOR_SHIFT); |
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| 79 | fsdata = libfat_get_sector(fs, fatsect); |
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| 80 | if (!fsdata) |
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| 81 | return -1; |
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| 82 | nextcluster = fsdata[fatoffset & LIBFAT_SECTOR_MASK]; |
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| 83 | |
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| 84 | /* Get second byte */ |
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| 85 | fatoffset++; |
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| 86 | fatsect = fs->fat + (fatoffset >> LIBFAT_SECTOR_SHIFT); |
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| 87 | fsdata = libfat_get_sector(fs, fatsect); |
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| 88 | if (!fsdata) |
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| 89 | return -1; |
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| 90 | nextcluster |= fsdata[fatoffset & LIBFAT_SECTOR_MASK] << 8; |
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| 91 | |
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| 92 | /* Extract the FAT entry */ |
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| 93 | if (cluster & 1) |
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| 94 | nextcluster >>= 4; |
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| 95 | else |
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| 96 | nextcluster &= 0x0FFF; |
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| 97 | |
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| 98 | if (nextcluster >= 0x0FF8) |
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| 99 | return 0; |
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| 100 | break; |
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| 101 | |
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| 102 | case FAT16: |
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| 103 | fatoffset = cluster << 1; |
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| 104 | fatsect = fs->fat + (fatoffset >> LIBFAT_SECTOR_SHIFT); |
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| 105 | fsdata = libfat_get_sector(fs, fatsect); |
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| 106 | if (!fsdata) |
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| 107 | return -1; |
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| 108 | nextcluster = |
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| 109 | read16((le16_t *) & fsdata[fatoffset & LIBFAT_SECTOR_MASK]); |
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| 110 | |
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| 111 | if (nextcluster >= 0x0FFF8) |
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| 112 | return 0; |
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| 113 | break; |
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| 114 | |
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| 115 | case FAT28: |
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| 116 | fatoffset = cluster << 2; |
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| 117 | fatsect = fs->fat + (fatoffset >> LIBFAT_SECTOR_SHIFT); |
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| 118 | fsdata = libfat_get_sector(fs, fatsect); |
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| 119 | if (!fsdata) |
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| 120 | return -1; |
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| 121 | nextcluster = |
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| 122 | read32((le32_t *) & fsdata[fatoffset & LIBFAT_SECTOR_MASK]); |
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| 123 | nextcluster &= 0x0FFFFFFF; |
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| 124 | |
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| 125 | if (nextcluster >= 0x0FFFFFF8) |
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| 126 | return 0; |
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| 127 | break; |
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| 128 | |
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| 129 | default: |
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| 130 | return -1; /* WTF? */ |
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| 131 | } |
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| 132 | |
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| 133 | return libfat_clustertosector(fs, nextcluster); |
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| 134 | } |
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