/*
 * fat_label - A utility to read the volume label off of a FAT filesystem.
 *
 * This utility will print out the volume label of a FAT filesystem if
 * it can find one. It knows how to cope with FAT12, FAT16, and FAT32
 * filesystems. The filesystem may be a device or a plain file
 * containing a filesystem.
 *
 * Copyright (c) 2007 Jeramey Crawford <jeramey@antihe.ro>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

 */

#include <sys/stat.h>
#include <sys/types.h>

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int fs_type (int);

int main (int argc, char ** argv)
{
	int i, fd, sr, fst;
	struct stat sb;
	char label[12];
	
	if (argc != 2) {
		printf("usage: fat_label filename\n");
		exit(0);
	}

	if ((sr = stat(argv[1], &sb)) == -1) {
		perror("fat_label");
		exit(1);
	}
	
	fd = open(argv[1], O_RDONLY, 0777);
	fst = fs_type(fd);
	bzero(&label, 12);

	/* seek to the right place to read the label */
	if (fst == 1) { 	/* FAT12/16 */
		if (lseek(fd, 0x2b, SEEK_SET) == -1) {
			perror("fat_label");
			exit(2);
		}
	}
	else if (fst == 2) {	/* FAT32 */
		if (lseek(fd, 0x47, SEEK_SET) == -1) {
			perror("fat_label");
			exit(2);
		}
	} else { 
		fprintf(stderr, "fat_label: Not a FAT filesystem\n");
		exit(3);
	}
	
	if (read(fd, &label, 11) == -1) {
		perror("fat_label");
		exit(2);
	}

	/* Strip out 0x20 padding at the end of the label. */
	for (i = 10; i; i--) {
		if (label[i] == 0x20)
			label[i] = 0;
		else
			break;
	}
	
	if (!strlen(label))
		fprintf(stderr, "fat_label: No label found\n");
	else
		printf("%s\n", label);
}

int fs_type (int fd)
/*
 * Return an integer describing the type of FAT found.
 *
 * 0 = No FAT
 * 1 = FAT12 or FAT16
 * 2 = FAT32
 * 
 */
{
	char *fst;

	fst = (char *)calloc(9, sizeof(char));
	if (!fst) {
		perror("fat_label: fstype");
		exit(2);
	}

        /* Try FAT12 or FAT16 first */
	if (lseek(fd, 0x36, SEEK_SET) == -1) {
		perror("fat_label: fs_type");
		exit(2);
	}

	if (read(fd, fst, 8) == -1) {
		perror("fat_label: fs_type");
		exit(2);
	}

	if (!strncmp(fst, "FAT12", 5)
	    || !strncmp(fst, "FAT16", 5))
		return 1;

	/* Maybe FAT32? */
	if (lseek(fd, 0x52, SEEK_SET) == -1) {
		perror("fat_label: fs_type");
		exit(2);
	}

	if (read(fd, fst, 8) == -1) {
		perror("fat_label: fs_type");
		exit(2);
	}

	if (!strncmp(fst, "FAT32", 5))
		return 2;

	return 0; /* no FAT type found */
}