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