source: MondoRescue/branches/3.3/mindi-busybox/util-linux/volume_id/exfat.c@ 3625

/*
 * volume_id - reads filesystem label and uuid
 *
 * Copyright (C) 2012 S-G Bergh <sgb@systemasis.org>
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

//kbuild:lib-$(CONFIG_FEATURE_VOLUMEID_EXFAT) += exfat.o

//config:
//config:config FEATURE_VOLUMEID_EXFAT
//config:   bool "exFAT filesystem"
//config:   default y
//config:   depends on VOLUMEID
//config:   help
//config:     exFAT (extended FAT) is a proprietary file system designed especially
//config:     for flash drives. It has many features from NTFS, but with less
//config:     overhead. exFAT is used on most SDXC cards for consumer electronics.
//config:

#include "volume_id_internal.h"

#define EXFAT_SB_OFFSET     0
#define EXFAT_DIR_ENTRY_SZ  32
#define EXFAT_MAX_DIR_ENTRIES   100

struct exfat_super_block {
/* 0x00 */  uint8_t     boot_jump[3];
/* 0x03 */  uint8_t     fs_name[8];
/* 0x0B */  uint8_t     must_be_zero[53];
/* 0x40 */  uint64_t    partition_offset;
/* 0x48 */  uint64_t    volume_length;
/* 0x50 */  uint32_t    fat_offset;     // Sector address of 1st FAT
/* 0x54 */  uint32_t    fat_size;       // In sectors
/* 0x58 */  uint32_t    cluster_heap_offset;    // Sector address of Data Region
/* 0x5C */  uint32_t    cluster_count;
/* 0x60 */  uint32_t    root_dir;       // Cluster address of Root Directory
/* 0x64 */  uint8_t     vol_serial_nr[4];   // Volume ID
/* 0x68 */  uint16_t    fs_revision;        // VV.MM
/* 0x6A */  uint16_t    vol_flags;
/* 0x6C */  uint8_t     bytes_per_sector;   // Power of 2: 9 => 512, 12 => 4096
/* 0x6D */  uint8_t     sectors_per_cluster;    // Power of 2
/* 0x6E */  uint8_t     nr_of_fats;     // 2 for TexFAT
/* 0x6F */  // ...
} PACKED;

struct exfat_dir_entry {
/* 0x00 */  uint8_t     entry_type;
        union {
            struct volume_label {
/* 0x01 */          uint8_t     char_count;     // Length of label
/* 0x02 */          uint16_t    vol_label[11];      // UTF16 string without null termination
/* 0x18 */          uint8_t     reserved[8];
/* 0x20 */      } PACKED label;
            struct volume_guid {
/* 0x01 */          uint8_t     sec_count;
/* 0x02 */          uint16_t    set_checksum;
/* 0x04 */          uint16_t    flags;
/* 0x06 */          uint8_t     vol_guid[16];
/* 0x16 */          uint8_t     reserved[10];
/* 0x20 */      } PACKED guid;
        } PACKED type;
} PACKED;

int FAST_FUNC volume_id_probe_exfat(struct volume_id *id /*,uint64_t off*/)
{
    struct exfat_super_block *sb;
    struct exfat_dir_entry *de;
    unsigned    sector_sz;
    unsigned    cluster_sz;
    uint64_t    root_dir_off;
    unsigned    count;
    unsigned    need_lbl_guid;

    // Primary super block
    dbg("exFAT: probing at offset 0x%x", EXFAT_SB_OFFSET);
    sb = volume_id_get_buffer(id, EXFAT_SB_OFFSET, sizeof(*sb));

    if (!sb)
        return -1;

    if (memcmp(sb->fs_name, "EXFAT   ", 8) != 0)
        return -1;

    sector_sz = 1 << sb->bytes_per_sector;
    cluster_sz = sector_sz << sb->sectors_per_cluster;
    // There are no clusters 0 and 1, so the first cluster is 2.
    root_dir_off = (uint64_t)EXFAT_SB_OFFSET +
        // Hmm... should we cast sector_sz/cluster_sz to uint64_t?
        (le32_to_cpu(sb->cluster_heap_offset)) * sector_sz +
        (le32_to_cpu(sb->root_dir) - 2) * cluster_sz;
    dbg("exFAT: sector size 0x%x bytes", sector_sz);
    dbg("exFAT: cluster size 0x%x bytes", cluster_sz);
    dbg("exFAT: root dir is at 0x%llx", (long long)root_dir_off);

    // Use DOS uuid as fallback, if no GUID set
    volume_id_set_uuid(id, sb->vol_serial_nr, UUID_DOS);

    // EXFAT_MAX_DIR_ENTRIES is used as a safety belt.
    // The Root Directory may hold an unlimited number of entries,
    // so we do not want to check all. Usually label and GUID
    // are in the beginning, but there are no guarantees.
    need_lbl_guid = (1 << 0) | (1 << 1);
    for (count = 0; count < EXFAT_MAX_DIR_ENTRIES; count++) {
        de = volume_id_get_buffer(id, root_dir_off + (count * EXFAT_DIR_ENTRY_SZ), EXFAT_DIR_ENTRY_SZ);
        if (de == NULL)
            break;
        if (de->entry_type == 0x00) {
            // End of Directory Marker
            dbg("exFAT: End of root directory reached after %u entries", count);
            break;
        }
        if (de->entry_type == 0x83) {
            // Volume Label Directory Entry
            volume_id_set_label_unicode16(id, (uint8_t *)de->type.label.vol_label,
                        LE, 2 * de->type.label.char_count);
            need_lbl_guid &= ~(1 << 0);
        }
        if (de->entry_type == 0xA0) {
            // Volume GUID Directory Entry
            volume_id_set_uuid(id, de->type.guid.vol_guid, UUID_DCE);
            need_lbl_guid &= ~(1 << 1);
        }
        if (!need_lbl_guid)
            break;
    }

    IF_FEATURE_BLKID_TYPE(id->type = "exfat";)
    return 0;
}