1 /* ----------------------------------------------------------------------- *
2 *
3 * Copyright 2004-2008 H. Peter Anvin - All Rights Reserved
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation, Inc., 53 Temple Place Ste 330,
8 * Boston MA 02111-1307, USA; either version 2 of the License, or
9 * (at your option) any later version; incorporated herein by reference.
10 *
11 * ----------------------------------------------------------------------- */
12
13 /*
14 * fatchain.c
15 *
16 * Follow a FAT chain
17 */
18
19 #include "libfatint.h"
20 #include "ulint.h"
21
22 /*
23 * Convert a cluster number (or 0 for the root directory) to a
24 * sector number. Return -1 on failure.
25 */
libfat_clustertosector(const struct libfat_filesystem * fs,int32_t cluster)26 libfat_sector_t libfat_clustertosector(const struct libfat_filesystem *fs,
27 int32_t cluster)
28 {
29 if (cluster == 0)
30 cluster = fs->rootcluster;
31
32 if (cluster == 0)
33 return fs->rootdir;
34 else if (cluster < 2 || cluster >= fs->endcluster)
35 return -1;
36 else
37 return fs->data + ((libfat_sector_t) (cluster - 2) << fs->clustshift);
38 }
39
40 /*
41 * Get the next sector of either the root directory or a FAT chain.
42 * Returns 0 on end of file and -1 on error.
43 */
44
libfat_nextsector(struct libfat_filesystem * fs,libfat_sector_t s)45 libfat_sector_t libfat_nextsector(struct libfat_filesystem * fs,
46 libfat_sector_t s)
47 {
48 int32_t cluster, nextcluster;
49 uint32_t fatoffset;
50 libfat_sector_t fatsect;
51 uint8_t *fsdata;
52 uint32_t clustmask = fs->clustsize - 1;
53 libfat_sector_t rs;
54
55 if (s < fs->data) {
56 if (s < fs->rootdir)
57 return -1;
58
59 /* Root directory */
60 s++;
61 return (s < fs->data) ? s : 0;
62 }
63
64 rs = s - fs->data;
65
66 if (~rs & clustmask)
67 return s + 1; /* Next sector in cluster */
68
69 cluster = 2 + (rs >> fs->clustshift);
70
71 if (cluster >= fs->endcluster)
72 return -1;
73
74 switch (fs->fat_type) {
75 case FAT12:
76 /* Get first byte */
77 fatoffset = cluster + (cluster >> 1);
78 fatsect = fs->fat + (fatoffset >> LIBFAT_SECTOR_SHIFT);
79 fsdata = libfat_get_sector(fs, fatsect);
80 if (!fsdata)
81 return -1;
82 nextcluster = fsdata[fatoffset & LIBFAT_SECTOR_MASK];
83
84 /* Get second byte */
85 fatoffset++;
86 fatsect = fs->fat + (fatoffset >> LIBFAT_SECTOR_SHIFT);
87 fsdata = libfat_get_sector(fs, fatsect);
88 if (!fsdata)
89 return -1;
90 nextcluster |= fsdata[fatoffset & LIBFAT_SECTOR_MASK] << 8;
91
92 /* Extract the FAT entry */
93 if (cluster & 1)
94 nextcluster >>= 4;
95 else
96 nextcluster &= 0x0FFF;
97
98 if (nextcluster >= 0x0FF8)
99 return 0;
100 break;
101
102 case FAT16:
103 fatoffset = cluster << 1;
104 fatsect = fs->fat + (fatoffset >> LIBFAT_SECTOR_SHIFT);
105 fsdata = libfat_get_sector(fs, fatsect);
106 if (!fsdata)
107 return -1;
108 nextcluster =
109 read16((le16_t *) & fsdata[fatoffset & LIBFAT_SECTOR_MASK]);
110
111 if (nextcluster >= 0x0FFF8)
112 return 0;
113 break;
114
115 case FAT28:
116 fatoffset = cluster << 2;
117 fatsect = fs->fat + (fatoffset >> LIBFAT_SECTOR_SHIFT);
118 fsdata = libfat_get_sector(fs, fatsect);
119 if (!fsdata)
120 return -1;
121 nextcluster =
122 read32((le32_t *) & fsdata[fatoffset & LIBFAT_SECTOR_MASK]);
123 nextcluster &= 0x0FFFFFFF;
124
125 if (nextcluster >= 0x0FFFFFF8)
126 return 0;
127 break;
128
129 default:
130 return -1; /* WTF? */
131 }
132
133 return libfat_clustertosector(fs, nextcluster);
134 }
135