/*
 * volume_id - reads filesystem label and uuid
 *
 * Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.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
 */
//config:config FEATURE_VOLUMEID_FAT
//config:       bool "fat filesystem"
//config:       default y
//config:       depends on VOLUMEID

//kbuild:lib-$(CONFIG_FEATURE_VOLUMEID_FAT) += fat.o

#include "volume_id_internal.h"

/* linux/msdos_fs.h says: */
#define FAT12_MAX                       0xff4
#define FAT16_MAX                       0xfff4
#define FAT32_MAX                       0x0ffffff6

#define FAT_ATTR_VOLUME_ID              0x08
#define FAT_ATTR_DIR                    0x10
#define FAT_ATTR_LONG_NAME              0x0f
#define FAT_ATTR_MASK                   0x3f
#define FAT_ENTRY_FREE                  0xe5

struct vfat_super_block {
        uint8_t         boot_jump[3];
        uint8_t         sysid[8];
        uint16_t        sector_size_bytes;
        uint8_t         sectors_per_cluster;
        uint16_t        reserved_sct;
        uint8_t         fats;
        uint16_t        dir_entries;
        uint16_t        sectors;
        uint8_t         media;
        uint16_t        fat_length;
        uint16_t        secs_track;
        uint16_t        heads;
        uint32_t        hidden;
        uint32_t        total_sect;
        union {
                struct fat_super_block {
                        uint8_t         unknown[3];
                        uint8_t         serno[4];
                        uint8_t         label[11];
                        uint8_t         magic[8];
                        uint8_t         dummy2[192];
                        uint8_t         pmagic[2];
                } PACKED fat;
                struct fat32_super_block {
                        uint32_t        fat32_length;
                        uint16_t        flags;
                        uint8_t         version[2];
                        uint32_t        root_cluster;
                        uint16_t        insfo_sector;
                        uint16_t        backup_boot;
                        uint16_t        reserved2[6];
                        uint8_t         unknown[3];
                        uint8_t         serno[4];
                        uint8_t         label[11];
                        uint8_t         magic[8];
                        uint8_t         dummy2[164];
                        uint8_t         pmagic[2];
                } PACKED fat32;
        } PACKED type;
} PACKED;

struct vfat_dir_entry {
        uint8_t         name[11];
        uint8_t         attr;
        uint16_t        time_creat;
        uint16_t        date_creat;
        uint16_t        time_acc;
        uint16_t        date_acc;
        uint16_t        cluster_high;
        uint16_t        time_write;
        uint16_t        date_write;
        uint16_t        cluster_low;
        uint32_t        size;
} PACKED;

static uint8_t *get_attr_volume_id(struct vfat_dir_entry *dir, int count)
{
        for (;--count >= 0; dir++) {
                /* end marker */
                if (dir->name[0] == 0x00) {
                        dbg("end of dir");
                        break;
                }

                /* empty entry */
                if (dir->name[0] == FAT_ENTRY_FREE)
                        continue;

                /* long name */
                if ((dir->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
                        continue;

                if ((dir->attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
                        /* labels do not have file data */
                        if (dir->cluster_high != 0 || dir->cluster_low != 0)
                                continue;

                        dbg("found ATTR_VOLUME_ID id in root dir");
                        return dir->name;
                }

                dbg("skip dir entry");
        }

        return NULL;
}

int FAST_FUNC volume_id_probe_vfat(struct volume_id *id /*,uint64_t fat_partition_off*/)
{
#define fat_partition_off ((uint64_t)0)
        struct vfat_super_block *vs;
        struct vfat_dir_entry *dir;
        uint16_t sector_size_bytes;
        uint16_t dir_entries;
        uint32_t sect_count;
        uint16_t reserved_sct;
        uint32_t fat_size_sct;
        uint32_t root_cluster;
        uint32_t dir_size_sct;
        uint32_t cluster_count;
        uint64_t root_start_off;
        uint32_t start_data_sct;
        uint8_t *buf;
        uint32_t buf_size;
        uint8_t *label = NULL;
        uint32_t next_cluster;
        int maxloop;

        dbg("probing at offset 0x%llx", (unsigned long long) fat_partition_off);

        vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
        if (vs == NULL)
                return -1;

        /* believe only that's fat, don't trust the version
         * the cluster_count will tell us
         */
        if (memcmp(vs->sysid, "NTFS", 4) == 0)
                return -1;

        if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
                goto valid;

        if (memcmp(vs->type.fat32.magic, "FAT32   ", 8) == 0)
                goto valid;

        if (memcmp(vs->type.fat.magic, "FAT16   ", 8) == 0)
                goto valid;

        if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
                goto valid;

        if (memcmp(vs->type.fat.magic, "FAT12   ", 8) == 0)
                goto valid;

        /*
         * There are old floppies out there without a magic, so we check
         * for well known values and guess if it's a fat volume
         */

        /* boot jump address check */
        if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90)
         && vs->boot_jump[0] != 0xe9
        ) {
                return -1;
        }

        /* heads check */
        if (vs->heads == 0)
                return -1;

        /* cluster size check */
        if (vs->sectors_per_cluster == 0
         || (vs->sectors_per_cluster & (vs->sectors_per_cluster-1))
        ) {
                return -1;
        }

        /* media check */
        if (vs->media < 0xf8 && vs->media != 0xf0)
                return -1;

        /* fat count*/
        if (vs->fats != 2)
                return -1;

 valid:
        /* sector size check */
        sector_size_bytes = le16_to_cpu(vs->sector_size_bytes);
        if (sector_size_bytes != 0x200 && sector_size_bytes != 0x400
         && sector_size_bytes != 0x800 && sector_size_bytes != 0x1000
        ) {
                return -1;
        }

        dbg("sector_size_bytes 0x%x", sector_size_bytes);
        dbg("sectors_per_cluster 0x%x", vs->sectors_per_cluster);

        reserved_sct = le16_to_cpu(vs->reserved_sct);
        dbg("reserved_sct 0x%x", reserved_sct);

        sect_count = le16_to_cpu(vs->sectors);
        if (sect_count == 0)
                sect_count = le32_to_cpu(vs->total_sect);
        dbg("sect_count 0x%x", sect_count);

        fat_size_sct = le16_to_cpu(vs->fat_length);
        if (fat_size_sct == 0)
                fat_size_sct = le32_to_cpu(vs->type.fat32.fat32_length);
        fat_size_sct *= vs->fats;
        dbg("fat_size_sct 0x%x", fat_size_sct);

        dir_entries = le16_to_cpu(vs->dir_entries);
        dir_size_sct = ((dir_entries * sizeof(struct vfat_dir_entry)) +
                        (sector_size_bytes-1)) / sector_size_bytes;
        dbg("dir_size_sct 0x%x", dir_size_sct);

        cluster_count = sect_count - (reserved_sct + fat_size_sct + dir_size_sct);
        cluster_count /= vs->sectors_per_cluster;
        dbg("cluster_count 0x%x", cluster_count);

//      if (cluster_count < FAT12_MAX) {
//              strcpy(id->type_version, "FAT12");
//      } else if (cluster_count < FAT16_MAX) {
//              strcpy(id->type_version, "FAT16");
//      } else {
//              strcpy(id->type_version, "FAT32");
//              goto fat32;
//      }
        if (cluster_count >= FAT16_MAX)
                goto fat32;

        /* the label may be an attribute in the root directory */
        root_start_off = (reserved_sct + fat_size_sct) * sector_size_bytes;
        dbg("root dir start 0x%llx", (unsigned long long) root_start_off);
        dbg("expected entries 0x%x", dir_entries);

        buf_size = dir_entries * sizeof(struct vfat_dir_entry);
        buf = volume_id_get_buffer(id, fat_partition_off + root_start_off, buf_size);
        if (buf == NULL)
                goto ret;

        label = get_attr_volume_id((struct vfat_dir_entry*) buf, dir_entries);

        vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
        if (vs == NULL)
                return -1;

        if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
//              volume_id_set_label_raw(id, label, 11);
                volume_id_set_label_string(id, label, 11);
        } else if (memcmp(vs->type.fat.label, "NO NAME    ", 11) != 0) {
//              volume_id_set_label_raw(id, vs->type.fat.label, 11);
                volume_id_set_label_string(id, vs->type.fat.label, 11);
        }
        volume_id_set_uuid(id, vs->type.fat.serno, UUID_DOS);
        goto ret;

 fat32:
        /* FAT32 root dir is a cluster chain like any other directory */
        buf_size = vs->sectors_per_cluster * sector_size_bytes;
        root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
        start_data_sct = reserved_sct + fat_size_sct;

        next_cluster = root_cluster;
        maxloop = 100;
        while (--maxloop) {
                uint64_t next_off_sct;
                uint64_t next_off;
                uint64_t fat_entry_off;
                int count;

                dbg("next_cluster 0x%x", (unsigned)next_cluster);
                next_off_sct = (uint64_t)(next_cluster - 2) * vs->sectors_per_cluster;
                next_off = (start_data_sct + next_off_sct) * sector_size_bytes;
                dbg("cluster offset 0x%llx", (unsigned long long) next_off);

                /* get cluster */
                buf = volume_id_get_buffer(id, fat_partition_off + next_off, buf_size);
                if (buf == NULL)
                        goto ret;

                dir = (struct vfat_dir_entry*) buf;
                count = buf_size / sizeof(struct vfat_dir_entry);
                dbg("expected entries 0x%x", count);

                label = get_attr_volume_id(dir, count);
                if (label)
                        break;

                /* get FAT entry */
                fat_entry_off = (reserved_sct * sector_size_bytes) + (next_cluster * sizeof(uint32_t));
                dbg("fat_entry_off 0x%llx", (unsigned long long)fat_entry_off);
                buf = volume_id_get_buffer(id, fat_partition_off + fat_entry_off, buf_size);
                if (buf == NULL)
                        goto ret;

                /* set next cluster */
                next_cluster = le32_to_cpu(*(uint32_t*)buf) & 0x0fffffff;
                if (next_cluster < 2 || next_cluster > FAT32_MAX)
                        break;
        }
        if (maxloop == 0)
                dbg("reached maximum follow count of root cluster chain, give up");

        vs = volume_id_get_buffer(id, fat_partition_off, 0x200);
        if (vs == NULL)
                return -1;

        if (label != NULL && memcmp(label, "NO NAME    ", 11) != 0) {
//              volume_id_set_label_raw(id, label, 11);
                volume_id_set_label_string(id, label, 11);
        } else if (memcmp(vs->type.fat32.label, "NO NAME    ", 11) != 0) {
//              volume_id_set_label_raw(id, vs->type.fat32.label, 11);
                volume_id_set_label_string(id, vs->type.fat32.label, 11);
        }
        volume_id_set_uuid(id, vs->type.fat32.serno, UUID_DOS);

 ret:
//      volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
        IF_FEATURE_BLKID_TYPE(id->type = "vfat";)

        return 0;
}