libblkid/src/superblocks/vfat.c - android_bootable_recovery - Gitiles

 /*
  * Copyright (C) 1999 by Andries Brouwer
  * Copyright (C) 1999, 2000, 2003 by Theodore Ts'o
  * Copyright (C) 2001 by Andreas Dilger
  * Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>
  * Copyright (C) 2008 Karel Zak <kzak@redhat.com>
  *
  * This file may be redistributed under the terms of the
  * GNU Lesser General Public License.
  */
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
 #include <errno.h>
 #include <ctype.h>
 #include <stdint.h>

 #include "superblocks.h"

 /* Yucky misaligned values */
 struct vfat_super_block {
 /* 00*/	unsigned char	vs_ignored[3];
 /* 03*/	unsigned char	vs_sysid[8];
 /* 0b*/	unsigned char	vs_sector_size[2];
 /* 0d*/	uint8_t		vs_cluster_size;
 /* 0e*/	uint16_t	vs_reserved;
 /* 10*/	uint8_t		vs_fats;
 /* 11*/	unsigned char	vs_dir_entries[2];
 /* 13*/	unsigned char	vs_sectors[2];
 /* 15*/	unsigned char	vs_media;
 /* 16*/	uint16_t	vs_fat_length;
 /* 18*/	uint16_t	vs_secs_track;
 /* 1a*/	uint16_t	vs_heads;
 /* 1c*/	uint32_t	vs_hidden;
 /* 20*/	uint32_t	vs_total_sect;
 /* 24*/	uint32_t	vs_fat32_length;
 /* 28*/	uint16_t	vs_flags;
 /* 2a*/	uint8_t		vs_version[2];
 /* 2c*/	uint32_t	vs_root_cluster;
 /* 30*/	uint16_t	vs_fsinfo_sector;
 /* 32*/	uint16_t	vs_backup_boot;
 /* 34*/	uint16_t	vs_reserved2[6];
 /* 40*/	unsigned char	vs_unknown[3];
 /* 43*/	unsigned char	vs_serno[4];
 /* 47*/	unsigned char	vs_label[11];
 /* 52*/	unsigned char   vs_magic[8];
 /* 5a*/	unsigned char	vs_dummy2[0x1fe - 0x5a];
 /*1fe*/	unsigned char	vs_pmagic[2];
 } __attribute__((packed));

 /* Yucky misaligned values */
 struct msdos_super_block {
 /* 00*/	unsigned char	ms_ignored[3];
 /* 03*/	unsigned char	ms_sysid[8];
 /* 0b*/	unsigned char	ms_sector_size[2];
 /* 0d*/	uint8_t		ms_cluster_size;
 /* 0e*/	uint16_t	ms_reserved;
 /* 10*/	uint8_t		ms_fats;
 /* 11*/	unsigned char	ms_dir_entries[2];
 /* 13*/	unsigned char	ms_sectors[2]; /* =0 iff V3 or later */
 /* 15*/	unsigned char	ms_media;
 /* 16*/	uint16_t	ms_fat_length; /* Sectors per FAT */
 /* 18*/	uint16_t	ms_secs_track;
 /* 1a*/	uint16_t	ms_heads;
 /* 1c*/	uint32_t	ms_hidden;
 /* V3 BPB */
 /* 20*/	uint32_t	ms_total_sect; /* iff ms_sectors == 0 */
 /* V4 BPB */
 /* 24*/	unsigned char	ms_unknown[3]; /* Phys drive no., resvd, V4 sig (0x29) */
 /* 27*/	unsigned char	ms_serno[4];
 /* 2b*/	unsigned char	ms_label[11];
 /* 36*/	unsigned char   ms_magic[8];
 /* 3e*/	unsigned char	ms_dummy2[0x1fe - 0x3e];
 /*1fe*/	unsigned char	ms_pmagic[2];
 } __attribute__((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;
 } __attribute__((packed));

 struct fat32_fsinfo {
 	uint8_t signature1[4];
 	uint32_t reserved1[120];
 	uint8_t signature2[4];
 	uint32_t free_clusters;
 	uint32_t next_cluster;
 	uint32_t reserved2[4];
 } __attribute__((packed));

 /* maximum number of clusters */
 #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

 static const char *no_name = "NO NAME    ";

 #define unaligned_le16(x) \
 		(((unsigned char *) x)[0] + (((unsigned char *) x)[1] << 8))

 /*
  * Look for LABEL (name) in the FAT root directory.
  */
 static unsigned char *search_fat_label(blkid_probe pr,
 				uint64_t offset, uint32_t entries)
 {
 	struct vfat_dir_entry *ent, *dir = NULL;
 	uint32_t i;

 	DBG(LOWPROBE, ul_debug("\tlook for label in root-dir "
 			"(entries: %d, offset: %jd)", entries, offset));

 	if (!blkid_probe_is_tiny(pr)) {
 		/* large disk, read whole root directory */
 		dir = (struct vfat_dir_entry *)
 			blkid_probe_get_buffer(pr,
 					offset,
 					(blkid_loff_t) entries *
 						sizeof(struct vfat_dir_entry));
 		if (!dir)
 			return NULL;
 	}

 	for (i = 0; i < entries; i++) {
 		/*
 		 * The root directory could be relatively large (4-16kB).
 		 * Fortunately, the LABEL is usually the first entry in the
 		 * directory. On tiny disks we call read() per entry.
 		 */
 		if (!dir)
 			ent = (struct vfat_dir_entry *)
 				blkid_probe_get_buffer(pr,
 					(blkid_loff_t) offset + (i *
 						sizeof(struct vfat_dir_entry)),
 					sizeof(struct vfat_dir_entry));
 		else
 			ent = &dir[i];

 		if (!ent || ent->name[0] == 0x00)
 			break;

 		if ((ent->name[0] == FAT_ENTRY_FREE) ||
 		    (ent->cluster_high != 0 || ent->cluster_low != 0) ||
 		    ((ent->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME))
 			continue;

 		if ((ent->attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) ==
 		    FAT_ATTR_VOLUME_ID) {
 			DBG(LOWPROBE, ul_debug("\tfound fs LABEL at entry %d", i));
 			return ent->name;
 		}
 	}
 	return NULL;
 }

 static int fat_valid_superblock(const struct blkid_idmag *mag,
 			struct msdos_super_block *ms,
 			struct vfat_super_block *vs,
 			uint32_t *cluster_count, uint32_t *fat_size)
 {
 	uint16_t sector_size, dir_entries, reserved;
 	uint32_t sect_count, __fat_size, dir_size, __cluster_count, fat_length;
 	uint32_t max_count;

 	/* extra check for FATs without magic strings */
 	if (mag->len <= 2) {
 		/* Old floppies have a valid MBR signature */
 		if (ms->ms_pmagic[0] != 0x55 || ms->ms_pmagic[1] != 0xAA)
 			return 0;

 		/*
 		 * OS/2 and apparently DFSee will place a FAT12/16-like
 		 * pseudo-superblock in the first 512 bytes of non-FAT
 		 * filesystems --- at least JFS and HPFS, and possibly others.
 		 * So we explicitly check for those filesystems at the
 		 * FAT12/16 filesystem magic field identifier, and if they are
 		 * present, we rule this out as a FAT filesystem, despite the
 		 * FAT-like pseudo-header.
 		 */
 		if ((memcmp(ms->ms_magic, "JFS     ", 8) == 0) ||
 		    (memcmp(ms->ms_magic, "HPFS    ", 8) == 0))
 			return 0;
 	}

 	/* fat counts(Linux kernel expects at least 1 FAT table) */
 	if (!ms->ms_fats)
 		return 0;
 	if (!ms->ms_reserved)
 		return 0;
 	if (!(0xf8 <= ms->ms_media || ms->ms_media == 0xf0))
 		return 0;
 	if (!is_power_of_2(ms->ms_cluster_size))
 		return 0;

 	sector_size = unaligned_le16(&ms->ms_sector_size);
 	if (!is_power_of_2(sector_size) ||
 	    sector_size < 512 || sector_size > 4096)
 		return 0;

 	dir_entries = unaligned_le16(&ms->ms_dir_entries);
 	reserved =  le16_to_cpu(ms->ms_reserved);
 	sect_count = unaligned_le16(&ms->ms_sectors);

 	if (sect_count == 0)
 		sect_count = le32_to_cpu(ms->ms_total_sect);

 	fat_length = le16_to_cpu(ms->ms_fat_length);
 	if (fat_length == 0)
 		fat_length = le32_to_cpu(vs->vs_fat32_length);

 	__fat_size = fat_length * ms->ms_fats;
 	dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
 					(sector_size-1)) / sector_size;

 	__cluster_count = (sect_count - (reserved + __fat_size + dir_size)) /
 							ms->ms_cluster_size;
 	if (!ms->ms_fat_length && vs->vs_fat32_length)
 		max_count = FAT32_MAX;
 	else
 		max_count = __cluster_count > FAT12_MAX ? FAT16_MAX : FAT12_MAX;

 	if (__cluster_count > max_count)
 		return 0;

 	if (fat_size)
 		*fat_size = __fat_size;
 	if (cluster_count)
 		*cluster_count = __cluster_count;

 	return 1;	/* valid */
 }

 /*
  * This function is used by MBR partition table parser to avoid
  * misinterpretation of FAT filesystem.
  */
 int blkid_probe_is_vfat(blkid_probe pr)
 {
 	struct vfat_super_block *vs;
 	struct msdos_super_block *ms;
 	const struct blkid_idmag *mag = NULL;
 	int rc;

 	rc = blkid_probe_get_idmag(pr, &vfat_idinfo, NULL, &mag);
 	if (rc < 0)
 		return rc;	/* error */
 	if (rc != BLKID_PROBE_OK || !mag)
 		return 0;

 	ms = blkid_probe_get_sb(pr, mag, struct msdos_super_block);
 	if (!ms)
 		return errno ? -errno : 0;
 	vs = blkid_probe_get_sb(pr, mag, struct vfat_super_block);
 	if (!vs)
 		return errno ? -errno : 0;

 	return fat_valid_superblock(mag, ms, vs, NULL, NULL);
 }

 /* FAT label extraction from the root directory taken from Kay
  * Sievers's volume_id library */
 static int probe_vfat(blkid_probe pr, const struct blkid_idmag *mag)
 {
 	struct vfat_super_block *vs;
 	struct msdos_super_block *ms;
 	const unsigned char *vol_label = 0;
 	unsigned char *vol_serno = NULL, vol_label_buf[11];
 	uint16_t sector_size = 0, reserved;
 	uint32_t cluster_count, fat_size;
 	const char *version = NULL;

 	ms = blkid_probe_get_sb(pr, mag, struct msdos_super_block);
 	if (!ms)
 		return errno ? -errno : 1;

 	vs = blkid_probe_get_sb(pr, mag, struct vfat_super_block);
 	if (!vs)
 		return errno ? -errno : 1;

 	if (!fat_valid_superblock(mag, ms, vs, &cluster_count, &fat_size))
 		return 1;

 	sector_size = unaligned_le16(&ms->ms_sector_size);
 	reserved =  le16_to_cpu(ms->ms_reserved);

 	if (ms->ms_fat_length) {
 		/* the label may be an attribute in the root directory */
 		uint32_t root_start = (reserved + fat_size) * sector_size;
 		uint32_t root_dir_entries = unaligned_le16(&vs->vs_dir_entries);

 		vol_label = search_fat_label(pr, root_start, root_dir_entries);
 		if (vol_label) {
 			memcpy(vol_label_buf, vol_label, 11);
 			vol_label = vol_label_buf;
 		}

 		if (!vol_label || !memcmp(vol_label, no_name, 11))
 			vol_label = ms->ms_label;
 		vol_serno = ms->ms_serno;

 		blkid_probe_set_value(pr, "SEC_TYPE", (unsigned char *) "msdos",
                               sizeof("msdos"));

 		if (cluster_count < FAT12_MAX)
 			version = "FAT12";
 		else if (cluster_count < FAT16_MAX)
 			version = "FAT16";

 	} else if (vs->vs_fat32_length) {
 		unsigned char *buf;
 		uint16_t fsinfo_sect;
 		int maxloop = 100;

 		/* Search the FAT32 root dir for the label attribute */
 		uint32_t buf_size = vs->vs_cluster_size * sector_size;
 		uint32_t start_data_sect = reserved + fat_size;
 		uint32_t entries = le32_to_cpu(vs->vs_fat32_length) *
 					sector_size / sizeof(uint32_t);
 		uint32_t next = le32_to_cpu(vs->vs_root_cluster);

 		while (next && next < entries && --maxloop) {
 			uint32_t next_sect_off;
 			uint64_t next_off, fat_entry_off;
 			int count;

 			next_sect_off = (next - 2) * vs->vs_cluster_size;
 			next_off = (uint64_t)(start_data_sect + next_sect_off) *
 				sector_size;

 			count = buf_size / sizeof(struct vfat_dir_entry);

 			vol_label = search_fat_label(pr, next_off, count);
 			if (vol_label) {
 				memcpy(vol_label_buf, vol_label, 11);
 				vol_label = vol_label_buf;
 				break;
 			}

 			/* get FAT entry */
 			fat_entry_off = ((uint64_t) reserved * sector_size) +
 				(next * sizeof(uint32_t));
 			buf = blkid_probe_get_buffer(pr, fat_entry_off, buf_size);
 			if (buf == NULL)
 				break;

 			/* set next cluster */
 			next = le32_to_cpu(*((uint32_t *) buf)) & 0x0fffffff;
 		}

 		version = "FAT32";

 		if (!vol_label || !memcmp(vol_label, no_name, 11))
 			vol_label = vs->vs_label;
 		vol_serno = vs->vs_serno;

 		/*
 		 * FAT32 should have a valid signature in the fsinfo block,
 		 * but also allow all bytes set to '\0', because some volumes
 		 * do not set the signature at all.
 		 */
 		fsinfo_sect = le16_to_cpu(vs->vs_fsinfo_sector);
 		if (fsinfo_sect) {
 			struct fat32_fsinfo *fsinfo;

 			buf = blkid_probe_get_buffer(pr,
 					(blkid_loff_t) fsinfo_sect * sector_size,
 					sizeof(struct fat32_fsinfo));
 			if (buf == NULL)
 				return errno ? -errno : 1;

 			fsinfo = (struct fat32_fsinfo *) buf;
 			if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0 &&
 			    memcmp(fsinfo->signature1, "\x52\x52\x64\x41", 4) != 0 &&
 			    memcmp(fsinfo->signature1, "\x00\x00\x00\x00", 4) != 0)
 				return 1;
 			if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0 &&
 			    memcmp(fsinfo->signature2, "\x00\x00\x00\x00", 4) != 0)
 				return 1;
 		}
 	}

 	if (vol_label && memcmp(vol_label, no_name, 11))
 		blkid_probe_set_label(pr, (unsigned char *) vol_label, 11);

 	/* We can't just print them as %04X, because they are unaligned */
 	if (vol_serno)
 		blkid_probe_sprintf_uuid(pr, vol_serno, 4, "%02X%02X-%02X%02X",
 			vol_serno[3], vol_serno[2], vol_serno[1], vol_serno[0]);
 	if (version)
 		blkid_probe_set_version(pr, version);

 	return 0;
 }


 const struct blkid_idinfo vfat_idinfo =
 {
 	.name		= "vfat",
 	.usage		= BLKID_USAGE_FILESYSTEM,
 	.probefunc	= probe_vfat,
 	.magics		=
 	{
 		{ .magic = "MSWIN",    .len = 5, .sboff = 0x52 },
 		{ .magic = "FAT32   ", .len = 8, .sboff = 0x52 },
 		{ .magic = "MSDOS",    .len = 5, .sboff = 0x36 },
 		{ .magic = "FAT16   ", .len = 8, .sboff = 0x36 },
 		{ .magic = "FAT12   ", .len = 8, .sboff = 0x36 },
 		{ .magic = "FAT     ", .len = 8, .sboff = 0x36 },
 		{ .magic = "\353",     .len = 1, },
 		{ .magic = "\351",     .len = 1, },
 		{ .magic = "\125\252", .len = 2, .sboff = 0x1fe },
 		{ NULL }
 	}
 };
	/*
	* Copyright (C) 1999 by Andries Brouwer
	* Copyright (C) 1999, 2000, 2003 by Theodore Ts'o
	* Copyright (C) 2001 by Andreas Dilger
	* Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>
	* Copyright (C) 2008 Karel Zak <kzak@redhat.com>
	*
	* This file may be redistributed under the terms of the
	* GNU Lesser General Public License.
	*/
	#include <stdio.h>
	#include <stdlib.h>
	#include <unistd.h>
	#include <string.h>
	#include <errno.h>
	#include <ctype.h>
	#include <stdint.h>

	#include "superblocks.h"

	/* Yucky misaligned values */
	struct vfat_super_block {
	/* 00*/ unsigned char vs_ignored[3];
	/* 03*/ unsigned char vs_sysid[8];
	/* 0b*/ unsigned char vs_sector_size[2];
	/* 0d*/ uint8_t vs_cluster_size;
	/* 0e*/ uint16_t vs_reserved;
	/* 10*/ uint8_t vs_fats;
	/* 11*/ unsigned char vs_dir_entries[2];
	/* 13*/ unsigned char vs_sectors[2];
	/* 15*/ unsigned char vs_media;
	/* 16*/ uint16_t vs_fat_length;
	/* 18*/ uint16_t vs_secs_track;
	/* 1a*/ uint16_t vs_heads;
	/* 1c*/ uint32_t vs_hidden;
	/* 20*/ uint32_t vs_total_sect;
	/* 24*/ uint32_t vs_fat32_length;
	/* 28*/ uint16_t vs_flags;
	/* 2a*/ uint8_t vs_version[2];
	/* 2c*/ uint32_t vs_root_cluster;
	/* 30*/ uint16_t vs_fsinfo_sector;
	/* 32*/ uint16_t vs_backup_boot;
	/* 34*/ uint16_t vs_reserved2[6];
	/* 40*/ unsigned char vs_unknown[3];
	/* 43*/ unsigned char vs_serno[4];
	/* 47*/ unsigned char vs_label[11];
	/* 52*/ unsigned char vs_magic[8];
	/* 5a*/ unsigned char vs_dummy2[0x1fe - 0x5a];
	/1fe/ unsigned char vs_pmagic[2];
	} __attribute__((packed));

	/* Yucky misaligned values */
	struct msdos_super_block {
	/* 00*/ unsigned char ms_ignored[3];
	/* 03*/ unsigned char ms_sysid[8];
	/* 0b*/ unsigned char ms_sector_size[2];
	/* 0d*/ uint8_t ms_cluster_size;
	/* 0e*/ uint16_t ms_reserved;
	/* 10*/ uint8_t ms_fats;
	/* 11*/ unsigned char ms_dir_entries[2];
	/* 13/ unsigned char ms_sectors[2]; / =0 iff V3 or later */
	/* 15*/ unsigned char ms_media;
	/* 16/ uint16_t ms_fat_length; / Sectors per FAT */
	/* 18*/ uint16_t ms_secs_track;
	/* 1a*/ uint16_t ms_heads;
	/* 1c*/ uint32_t ms_hidden;
	/* V3 BPB */
	/* 20/ uint32_t ms_total_sect; / iff ms_sectors == 0 */
	/* V4 BPB */
	/* 24/ unsigned char ms_unknown[3]; / Phys drive no., resvd, V4 sig (0x29) */
	/* 27*/ unsigned char ms_serno[4];
	/* 2b*/ unsigned char ms_label[11];
	/* 36*/ unsigned char ms_magic[8];
	/* 3e*/ unsigned char ms_dummy2[0x1fe - 0x3e];
	/1fe/ unsigned char ms_pmagic[2];
	} __attribute__((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;
	} __attribute__((packed));

	struct fat32_fsinfo {
	uint8_t signature1[4];
	uint32_t reserved1[120];
	uint8_t signature2[4];
	uint32_t free_clusters;
	uint32_t next_cluster;
	uint32_t reserved2[4];
	} __attribute__((packed));

	/* maximum number of clusters */
	#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

	static const char *no_name = "NO NAME ";

	#define unaligned_le16(x) \
	(((unsigned char ) x)[0] + (((unsigned char ) x)[1] << 8))

	/*
	* Look for LABEL (name) in the FAT root directory.
	*/
	static unsigned char *search_fat_label(blkid_probe pr,
	uint64_t offset, uint32_t entries)
	{
	struct vfat_dir_entry ent, dir = NULL;
	uint32_t i;

	DBG(LOWPROBE, ul_debug("\tlook for label in root-dir "
	"(entries: %d, offset: %jd)", entries, offset));

	if (!blkid_probe_is_tiny(pr)) {
	/* large disk, read whole root directory */
	dir = (struct vfat_dir_entry *)
	blkid_probe_get_buffer(pr,
	offset,
	(blkid_loff_t) entries *
	sizeof(struct vfat_dir_entry));
	if (!dir)
	return NULL;
	}

	for (i = 0; i < entries; i++) {
	/*
	* The root directory could be relatively large (4-16kB).
	* Fortunately, the LABEL is usually the first entry in the
	* directory. On tiny disks we call read() per entry.
	*/
	if (!dir)
	ent = (struct vfat_dir_entry *)
	blkid_probe_get_buffer(pr,
	(blkid_loff_t) offset + (i *
	sizeof(struct vfat_dir_entry)),
	sizeof(struct vfat_dir_entry));
	else
	ent = &dir[i];

	if (!ent \|\| ent->name[0] == 0x00)
	break;

	if ((ent->name[0] == FAT_ENTRY_FREE) \|\|
	(ent->cluster_high != 0 \|\| ent->cluster_low != 0) \|\|
	((ent->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME))
	continue;

	if ((ent->attr & (FAT_ATTR_VOLUME_ID \| FAT_ATTR_DIR)) ==
	FAT_ATTR_VOLUME_ID) {
	DBG(LOWPROBE, ul_debug("\tfound fs LABEL at entry %d", i));
	return ent->name;
	}
	}
	return NULL;
	}

	static int fat_valid_superblock(const struct blkid_idmag *mag,
	struct msdos_super_block *ms,
	struct vfat_super_block *vs,
	uint32_t cluster_count, uint32_t fat_size)
	{
	uint16_t sector_size, dir_entries, reserved;
	uint32_t sect_count, __fat_size, dir_size, __cluster_count, fat_length;
	uint32_t max_count;

	/* extra check for FATs without magic strings */
	if (mag->len <= 2) {
	/* Old floppies have a valid MBR signature */
	if (ms->ms_pmagic[0] != 0x55 \|\| ms->ms_pmagic[1] != 0xAA)
	return 0;

	/*
	* OS/2 and apparently DFSee will place a FAT12/16-like
	* pseudo-superblock in the first 512 bytes of non-FAT
	* filesystems --- at least JFS and HPFS, and possibly others.
	* So we explicitly check for those filesystems at the
	* FAT12/16 filesystem magic field identifier, and if they are
	* present, we rule this out as a FAT filesystem, despite the
	* FAT-like pseudo-header.
	*/
	if ((memcmp(ms->ms_magic, "JFS ", 8) == 0) \|\|
	(memcmp(ms->ms_magic, "HPFS ", 8) == 0))
	return 0;
	}

	/* fat counts(Linux kernel expects at least 1 FAT table) */
	if (!ms->ms_fats)
	return 0;
	if (!ms->ms_reserved)
	return 0;
	if (!(0xf8 <= ms->ms_media \|\| ms->ms_media == 0xf0))
	return 0;
	if (!is_power_of_2(ms->ms_cluster_size))
	return 0;

	sector_size = unaligned_le16(&ms->ms_sector_size);
	if (!is_power_of_2(sector_size) \|\|
	sector_size < 512 \|\| sector_size > 4096)
	return 0;

	dir_entries = unaligned_le16(&ms->ms_dir_entries);
	reserved = le16_to_cpu(ms->ms_reserved);
	sect_count = unaligned_le16(&ms->ms_sectors);

	if (sect_count == 0)
	sect_count = le32_to_cpu(ms->ms_total_sect);

	fat_length = le16_to_cpu(ms->ms_fat_length);
	if (fat_length == 0)
	fat_length = le32_to_cpu(vs->vs_fat32_length);

	__fat_size = fat_length * ms->ms_fats;
	dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
	(sector_size-1)) / sector_size;

	__cluster_count = (sect_count - (reserved + __fat_size + dir_size)) /
	ms->ms_cluster_size;
	if (!ms->ms_fat_length && vs->vs_fat32_length)
	max_count = FAT32_MAX;
	else
	max_count = __cluster_count > FAT12_MAX ? FAT16_MAX : FAT12_MAX;

	if (__cluster_count > max_count)
	return 0;

	if (fat_size)
	*fat_size = __fat_size;
	if (cluster_count)
	*cluster_count = __cluster_count;

	return 1; /* valid */
	}

	/*
	* This function is used by MBR partition table parser to avoid
	* misinterpretation of FAT filesystem.
	*/
	int blkid_probe_is_vfat(blkid_probe pr)
	{
	struct vfat_super_block *vs;
	struct msdos_super_block *ms;
	const struct blkid_idmag *mag = NULL;
	int rc;

	rc = blkid_probe_get_idmag(pr, &vfat_idinfo, NULL, &mag);
	if (rc < 0)
	return rc; /* error */
	if (rc != BLKID_PROBE_OK \|\| !mag)
	return 0;

	ms = blkid_probe_get_sb(pr, mag, struct msdos_super_block);
	if (!ms)
	return errno ? -errno : 0;
	vs = blkid_probe_get_sb(pr, mag, struct vfat_super_block);
	if (!vs)
	return errno ? -errno : 0;

	return fat_valid_superblock(mag, ms, vs, NULL, NULL);
	}

	/* FAT label extraction from the root directory taken from Kay
	* Sievers's volume_id library */
	static int probe_vfat(blkid_probe pr, const struct blkid_idmag *mag)
	{
	struct vfat_super_block *vs;
	struct msdos_super_block *ms;
	const unsigned char *vol_label = 0;
	unsigned char *vol_serno = NULL, vol_label_buf[11];
	uint16_t sector_size = 0, reserved;
	uint32_t cluster_count, fat_size;
	const char *version = NULL;

	ms = blkid_probe_get_sb(pr, mag, struct msdos_super_block);
	if (!ms)
	return errno ? -errno : 1;

	vs = blkid_probe_get_sb(pr, mag, struct vfat_super_block);
	if (!vs)
	return errno ? -errno : 1;

	if (!fat_valid_superblock(mag, ms, vs, &cluster_count, &fat_size))
	return 1;

	sector_size = unaligned_le16(&ms->ms_sector_size);
	reserved = le16_to_cpu(ms->ms_reserved);

	if (ms->ms_fat_length) {
	/* the label may be an attribute in the root directory */
	uint32_t root_start = (reserved + fat_size) * sector_size;
	uint32_t root_dir_entries = unaligned_le16(&vs->vs_dir_entries);

	vol_label = search_fat_label(pr, root_start, root_dir_entries);
	if (vol_label) {
	memcpy(vol_label_buf, vol_label, 11);
	vol_label = vol_label_buf;
	}

	if (!vol_label \|\| !memcmp(vol_label, no_name, 11))
	vol_label = ms->ms_label;
	vol_serno = ms->ms_serno;

	blkid_probe_set_value(pr, "SEC_TYPE", (unsigned char *) "msdos",
	sizeof("msdos"));

	if (cluster_count < FAT12_MAX)
	version = "FAT12";
	else if (cluster_count < FAT16_MAX)
	version = "FAT16";

	} else if (vs->vs_fat32_length) {
	unsigned char *buf;
	uint16_t fsinfo_sect;
	int maxloop = 100;

	/* Search the FAT32 root dir for the label attribute */
	uint32_t buf_size = vs->vs_cluster_size * sector_size;
	uint32_t start_data_sect = reserved + fat_size;
	uint32_t entries = le32_to_cpu(vs->vs_fat32_length) *
	sector_size / sizeof(uint32_t);
	uint32_t next = le32_to_cpu(vs->vs_root_cluster);

	while (next && next < entries && --maxloop) {
	uint32_t next_sect_off;
	uint64_t next_off, fat_entry_off;
	int count;

	next_sect_off = (next - 2) * vs->vs_cluster_size;
	next_off = (uint64_t)(start_data_sect + next_sect_off) *
	sector_size;

	count = buf_size / sizeof(struct vfat_dir_entry);

	vol_label = search_fat_label(pr, next_off, count);
	if (vol_label) {
	memcpy(vol_label_buf, vol_label, 11);
	vol_label = vol_label_buf;
	break;
	}

	/* get FAT entry */
	fat_entry_off = ((uint64_t) reserved * sector_size) +
	(next * sizeof(uint32_t));
	buf = blkid_probe_get_buffer(pr, fat_entry_off, buf_size);
	if (buf == NULL)
	break;

	/* set next cluster */
	next = le32_to_cpu(((uint32_t ) buf)) & 0x0fffffff;
	}

	version = "FAT32";

	if (!vol_label \|\| !memcmp(vol_label, no_name, 11))
	vol_label = vs->vs_label;
	vol_serno = vs->vs_serno;

	/*
	* FAT32 should have a valid signature in the fsinfo block,
	* but also allow all bytes set to '\0', because some volumes
	* do not set the signature at all.
	*/
	fsinfo_sect = le16_to_cpu(vs->vs_fsinfo_sector);
	if (fsinfo_sect) {
	struct fat32_fsinfo *fsinfo;

	buf = blkid_probe_get_buffer(pr,
	(blkid_loff_t) fsinfo_sect * sector_size,
	sizeof(struct fat32_fsinfo));
	if (buf == NULL)
	return errno ? -errno : 1;

	fsinfo = (struct fat32_fsinfo *) buf;
	if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0 &&
	memcmp(fsinfo->signature1, "\x52\x52\x64\x41", 4) != 0 &&
	memcmp(fsinfo->signature1, "\x00\x00\x00\x00", 4) != 0)
	return 1;
	if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0 &&
	memcmp(fsinfo->signature2, "\x00\x00\x00\x00", 4) != 0)
	return 1;
	}
	}

	if (vol_label && memcmp(vol_label, no_name, 11))
	blkid_probe_set_label(pr, (unsigned char *) vol_label, 11);

	/* We can't just print them as %04X, because they are unaligned */
	if (vol_serno)
	blkid_probe_sprintf_uuid(pr, vol_serno, 4, "%02X%02X-%02X%02X",
	vol_serno[3], vol_serno[2], vol_serno[1], vol_serno[0]);
	if (version)
	blkid_probe_set_version(pr, version);

	return 0;
	}


	const struct blkid_idinfo vfat_idinfo =
	{
	.name = "vfat",
	.usage = BLKID_USAGE_FILESYSTEM,
	.probefunc = probe_vfat,
	.magics =
	{
	{ .magic = "MSWIN", .len = 5, .sboff = 0x52 },
	{ .magic = "FAT32 ", .len = 8, .sboff = 0x52 },
	{ .magic = "MSDOS", .len = 5, .sboff = 0x36 },
	{ .magic = "FAT16 ", .len = 8, .sboff = 0x36 },
	{ .magic = "FAT12 ", .len = 8, .sboff = 0x36 },
	{ .magic = "FAT ", .len = 8, .sboff = 0x36 },
	{ .magic = "\353", .len = 1, },
	{ .magic = "\351", .len = 1, },
	{ .magic = "\125\252", .len = 2, .sboff = 0x1fe },
	{ NULL }
	}
	};