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