util-linux/volume_id/fat.c

   1 /*
   2  * volume_id - reads filesystem label and uuid
   3  *
   4  * Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>
   5  *
   6  *      This library is free software; you can redistribute it and/or
   7  *      modify it under the terms of the GNU Lesser General Public
   8  *      License as published by the Free Software Foundation; either
   9  *      version 2.1 of the License, or (at your option) any later version.
  10  *
  11  *      This library is distributed in the hope that it will be useful,
  12  *      but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14  *      Lesser General Public License for more details.
  15  *
  16  *      You should have received a copy of the GNU Lesser General Public
  17  *      License along with this library; if not, write to the Free Software
  18  *      Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  19  */
  20
  21 //kbuild:lib-$(CONFIG_FEATURE_VOLUMEID_FAT) += fat.o
  22
  23 //config:
  24 //config:config FEATURE_VOLUMEID_FAT
  25 //config:       bool "fat filesystem"
  26 //config:       default y
  27 //config:       depends on VOLUMEID
  28 //config:       help
  29 //config:         TODO
  30 //config:
  31
  32 #include "volume_id_internal.h"
  33
  34 /* linux/msdos_fs.h says: */
  35 #define FAT12_MAX                       0xff4
  36 #define FAT16_MAX                       0xfff4
  37 #define FAT32_MAX                       0x0ffffff6
  38
  39 #define FAT_ATTR_VOLUME_ID              0x08
  40 #define FAT_ATTR_DIR                    0x10
  41 #define FAT_ATTR_LONG_NAME              0x0f
  42 #define FAT_ATTR_MASK                   0x3f
  43 #define FAT_ENTRY_FREE                  0xe5
  44
  45 struct vfat_super_block {
  46         uint8_t         boot_jump[3];
  47         uint8_t         sysid[8];
  48         uint16_t        sector_size_bytes;
  49         uint8_t         sectors_per_cluster;
  50         uint16_t        reserved_sct;
  51         uint8_t         fats;
  52         uint16_t        dir_entries;
  53         uint16_t        sectors;
  54         uint8_t         media;
  55         uint16_t        fat_length;
  56         uint16_t        secs_track;
  57         uint16_t        heads;
  58         uint32_t        hidden;
  59         uint32_t        total_sect;
  60         union {
  61                 struct fat_super_block {
  62                         uint8_t         unknown[3];
  63                         uint8_t         serno[4];
  64                         uint8_t         label[11];
  65                         uint8_t         magic[8];
  66                         uint8_t         dummy2[192];
  67                         uint8_t         pmagic[2];
  68                 } PACKED fat;
  69                 struct fat32_super_block {
  70                         uint32_t        fat32_length;
  71                         uint16_t        flags;
  72                         uint8_t         version[2];
  73                         uint32_t        root_cluster;
  74                         uint16_t        insfo_sector;
  75                         uint16_t        backup_boot;
  76                         uint16_t        reserved2[6];
  77                         uint8_t         unknown[3];
  78                         uint8_t         serno[4];
  79                         uint8_t         label[11];
  80                         uint8_t         magic[8];
  81                         uint8_t         dummy2[164];
  82                         uint8_t         pmagic[2];
  83                 } PACKED fat32;
  84         } PACKED type;
  85 } PACKED;
  86
  87 struct vfat_dir_entry {
  88         uint8_t         name[11];
  89         uint8_t         attr;
  90         uint16_t        time_creat;
  91         uint16_t        date_creat;
  92         uint16_t        time_acc;
  93         uint16_t        date_acc;
  94         uint16_t        cluster_high;
  95         uint16_t        time_write;
  96         uint16_t        date_write;
  97         uint16_t        cluster_low;
  98         uint32_t        size;
  99 } PACKED;
 100
 101 static uint8_t *get_attr_volume_id(struct vfat_dir_entry *dir, int count)
 102 {
 103         for (;--count >= 0; dir++) {
 104                 /* end marker */
 105                 if (dir->name[0] == 0x00) {
 106                         dbg("end of dir");
 107                         break;
 108                 }
 109
 110                 /* empty entry */
 111                 if (dir->name[0] == FAT_ENTRY_FREE)
 112                         continue;
 113
 114                 /* long name */
 115                 if ((dir->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
 116                         continue;
 117
 118                 if ((dir->attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
 119                         /* labels do not have file data */
 120                         if (dir->cluster_high != 0 || dir->cluster_low != 0)
 121                                 continue;
 122
 123                         dbg("found ATTR_VOLUME_ID id in root dir");
 124                         return dir->name;
 125                 }
 126
 127                 dbg("skip dir entry");
 128         }
 129
 130         return NULL;
 131 }
 132
 133 int FAST_FUNC volume_id_probe_vfat(struct volume_id *id /*,uint64_t fat_partition_off*/)
 134 {
 135 #define fat_partition_off ((uint64_t)0)
 136         struct vfat_super_block *vs;
 137         struct vfat_dir_entry *dir;
 138         uint16_t sector_size_bytes;
 139         uint16_t dir_entries;
 140         uint32_t sect_count;
 141         uint16_t reserved_sct;
 142         uint32_t fat_size_sct;
 143         uint32_t root_cluster;
 144         uint32_t dir_size_sct;
 145         uint32_t cluster_count;
 146         uint64_t root_start_off;
 147         uint32_t start_data_sct;
 148         uint8_t *buf;
 149         uint32_t buf_size;
 150         uint8_t *label = NULL;
 151         uint32_t next_cluster;
 152         int maxloop;
 153
 154         dbg("probing at offset 0x%llx", (unsigned long long) fat_partition_off);
 155
 156         vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
 157         if (vs == NULL)
 158                 return -1;
 159
 160         /* believe only that's fat, don't trust the version
 161          * the cluster_count will tell us
 162          */
 163         if (memcmp(vs->sysid, "NTFS", 4) == 0)
 164                 return -1;
 165
 166         if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
 167                 goto valid;
 168
 169         if (memcmp(vs->type.fat32.magic, "FAT32   ", 8) == 0)
 170                 goto valid;
 171
 172         if (memcmp(vs->type.fat.magic, "FAT16   ", 8) == 0)
 173                 goto valid;
 174
 175         if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
 176                 goto valid;
 177
 178         if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
 179                 goto valid;
 180
 181         /*
 182          * There are old floppies out there without a magic, so we check
 183          * for well known values and guess if it's a fat volume
 184          */
 185
 186         /* boot jump address check */
 187         if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90)
 188          && vs->boot_jump[0] != 0xe9
 189         ) {
 190                 return -1;
 191         }
 192
 193         /* heads check */
 194         if (vs->heads == 0)
 195                 return -1;
 196
 197         /* cluster size check */
 198         if (vs->sectors_per_cluster == 0
 199          || (vs->sectors_per_cluster & (vs->sectors_per_cluster-1))
 200         ) {
 201                 return -1;
 202         }
 203
 204         /* media check */
 205         if (vs->media < 0xf8 && vs->media != 0xf0)
 206                 return -1;
 207
 208         /* fat count*/
 209         if (vs->fats != 2)
 210                 return -1;
 211
 212  valid:
 213         /* sector size check */
 214         sector_size_bytes = le16_to_cpu(vs->sector_size_bytes);
 215         if (sector_size_bytes != 0x200 && sector_size_bytes != 0x400
 216          && sector_size_bytes != 0x800 && sector_size_bytes != 0x1000
 217         ) {
 218                 return -1;
 219         }
 220
 221         dbg("sector_size_bytes 0x%x", sector_size_bytes);
 222         dbg("sectors_per_cluster 0x%x", vs->sectors_per_cluster);
 223
 224         reserved_sct = le16_to_cpu(vs->reserved_sct);
 225         dbg("reserved_sct 0x%x", reserved_sct);
 226
 227         sect_count = le16_to_cpu(vs->sectors);
 228         if (sect_count == 0)
 229                 sect_count = le32_to_cpu(vs->total_sect);
 230         dbg("sect_count 0x%x", sect_count);
 231
 232         fat_size_sct = le16_to_cpu(vs->fat_length);
 233         if (fat_size_sct == 0)
 234                 fat_size_sct = le32_to_cpu(vs->type.fat32.fat32_length);
 235         fat_size_sct *= vs->fats;
 236         dbg("fat_size_sct 0x%x", fat_size_sct);
 237
 238         dir_entries = le16_to_cpu(vs->dir_entries);
 239         dir_size_sct = ((dir_entries * sizeof(struct vfat_dir_entry)) +
 240                         (sector_size_bytes-1)) / sector_size_bytes;
 241         dbg("dir_size_sct 0x%x", dir_size_sct);
 242
 243         cluster_count = sect_count - (reserved_sct + fat_size_sct + dir_size_sct);
 244         cluster_count /= vs->sectors_per_cluster;
 245         dbg("cluster_count 0x%x", cluster_count);
 246
 247 //      if (cluster_count < FAT12_MAX) {
 248 //              strcpy(id->type_version, "FAT12");
 249 //      } else if (cluster_count < FAT16_MAX) {
 250 //              strcpy(id->type_version, "FAT16");
 251 //      } else {
 252 //              strcpy(id->type_version, "FAT32");
 253 //              goto fat32;
 254 //      }
 255         if (cluster_count >= FAT16_MAX)
 256                 goto fat32;
 257
 258         /* the label may be an attribute in the root directory */
 259         root_start_off = (reserved_sct + fat_size_sct) * sector_size_bytes;
 260         dbg("root dir start 0x%llx", (unsigned long long) root_start_off);
 261         dbg("expected entries 0x%x", dir_entries);
 262
 263         buf_size = dir_entries * sizeof(struct vfat_dir_entry);
 264         buf = volume_id_get_buffer(id, fat_partition_off + root_start_off, buf_size);
 265         if (buf == NULL)
 266                 goto ret;
 267
 268         label = get_attr_volume_id((struct vfat_dir_entry*) buf, dir_entries);
 269
 270         vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
 271         if (vs == NULL)
 272                 return -1;
 273
 274         if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
 275 //              volume_id_set_label_raw(id, label, 11);
 276                 volume_id_set_label_string(id, label, 11);
 277         } else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
 278 //              volume_id_set_label_raw(id, vs->type.fat.label, 11);
 279                 volume_id_set_label_string(id, vs->type.fat.label, 11);
 280         }
 281         volume_id_set_uuid(id, vs->type.fat.serno, UUID_DOS);
 282         goto ret;
 283
 284  fat32:
 285         /* FAT32 root dir is a cluster chain like any other directory */
 286         buf_size = vs->sectors_per_cluster * sector_size_bytes;
 287         root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
 288         start_data_sct = reserved_sct + fat_size_sct;
 289
 290         next_cluster = root_cluster;
 291         maxloop = 100;
 292         while (--maxloop) {
 293                 uint64_t next_off_sct;
 294                 uint64_t next_off;
 295                 uint64_t fat_entry_off;
 296                 int count;
 297
 298                 dbg("next_cluster 0x%x", (unsigned)next_cluster);
 299                 next_off_sct = (uint64_t)(next_cluster - 2) * vs->sectors_per_cluster;
 300                 next_off = (start_data_sct + next_off_sct) * sector_size_bytes;
 301                 dbg("cluster offset 0x%llx", (unsigned long long) next_off);
 302
 303                 /* get cluster */
 304                 buf = volume_id_get_buffer(id, fat_partition_off + next_off, buf_size);
 305                 if (buf == NULL)
 306                         goto ret;
 307
 308                 dir = (struct vfat_dir_entry*) buf;
 309                 count = buf_size / sizeof(struct vfat_dir_entry);
 310                 dbg("expected entries 0x%x", count);
 311
 312                 label = get_attr_volume_id(dir, count);
 313                 if (label)
 314                         break;
 315
 316                 /* get FAT entry */
 317                 fat_entry_off = (reserved_sct * sector_size_bytes) + (next_cluster * sizeof(uint32_t));
 318                 dbg("fat_entry_off 0x%llx", (unsigned long long)fat_entry_off);
 319                 buf = volume_id_get_buffer(id, fat_partition_off + fat_entry_off, buf_size);
 320                 if (buf == NULL)
 321                         goto ret;
 322
 323                 /* set next cluster */
 324                 next_cluster = le32_to_cpu(*(uint32_t*)buf) & 0x0fffffff;
 325                 if (next_cluster < 2 || next_cluster > FAT32_MAX)
 326                         break;
 327         }
 328         if (maxloop == 0)
 329                 dbg("reached maximum follow count of root cluster chain, give up");
 330
 331         vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
 332         if (vs == NULL)
 333                 return -1;
 334
 335         if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
 336 //              volume_id_set_label_raw(id, label, 11);
 337                 volume_id_set_label_string(id, label, 11);
 338         } else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
 339 //              volume_id_set_label_raw(id, vs->type.fat32.label, 11);
 340                 volume_id_set_label_string(id, vs->type.fat32.label, 11);
 341         }
 342         volume_id_set_uuid(id, vs->type.fat32.serno, UUID_DOS);
 343
 344  ret:
 345 //      volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
 346         IF_FEATURE_BLKID_TYPE(id->type = "vfat";)
 347
 348         return 0;
 349 }