misc/e2label.c

/*
 * e2label.c		- Print or change the volume label on an ext2 fs
 *
 * aeb, 970714
 *
 */

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <ctype.h>
#include <termios.h>
#include <time.h>
#ifdef HAVE_GETOPT_H
#include <getopt.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#ifdef HAVE_ERRNO_H
#include <errno.h>
#endif

#define EXT2_SUPER_MAGIC 0xEF53

#define VOLNAMSZ 16

struct ext2_super_block {
	char  s_dummy0[56];
	unsigned char  s_magic[2];
	char  s_dummy1[62];
	char  s_volume_name[VOLNAMSZ];
	char  s_last_mounted[64];
	char  s_dummy2[824];
} sb;

int
open_e2fs (char *dev, int mode) {
	int fd;

	fd = open(dev, mode);
	if (fd < 0) {
	     perror(dev);
	     fprintf (stderr, "e2label: cannot open %s\n", dev);
	     exit(1);
	}
	if (lseek(fd, 1024, SEEK_SET) != 1024) {
	     perror(dev);
	     fprintf (stderr, "e2label: cannot seek to superblock\n");
	     exit(1);
	}
	if (read(fd, (char *) &sb, sizeof(sb)) != sizeof(sb)) {
	     perror(dev);
	     fprintf (stderr, "e2label: error reading superblock\n");
	     exit(1);
	}
	if (sb.s_magic[0] + 256*sb.s_magic[1] != EXT2_SUPER_MAGIC) {
	     fprintf (stderr, "e2label: not an ext2 filesystem\n");
	     exit(1);
	}

	return fd;
}

void
print_label (char *dev) {
	char label[VOLNAMSZ+1];

	open_e2fs (dev, O_RDONLY);
	label[VOLNAMSZ] = 0;
	strncpy(label, sb.s_volume_name, VOLNAMSZ);
	printf("%s\n", label);
}

void
change_label (char *dev, char *label) {
	int fd;

	fd = open_e2fs(dev, O_RDWR);
	memset(sb.s_volume_name, 0, VOLNAMSZ);
	strncpy(sb.s_volume_name, label, VOLNAMSZ);
	if (lseek(fd, 1024, SEEK_SET) != 1024) {
	     perror(dev);
	     fprintf (stderr, "e2label: cannot seek to superblock again\n");
	     exit(1);
	}
	if (write(fd, (char *) &sb, sizeof(sb)) != sizeof(sb)) {
	     perror(dev);
	     fprintf (stderr, "e2label: error writing superblock\n");
	     exit(1);
	}
}

int
main (int argc, char ** argv) {
	if (argc == 2)
	     print_label(argv[1]);
	else if (argc == 3)
	     change_label(argv[1], argv[2]);
	else {
	     fprintf(stderr, "Usage: e2label device [newlabel]\n");
	     exit(1);
	}
	return 0;
}