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