1/*
2 * Zero out a superblock check hash.
3 * By Kirk McKusick <mckusick@mckusick.com>
4 */
5
6#include <sys/param.h>
7#include <sys/disklabel.h>
8
9#include <ufs/ufs/dinode.h>
10#include <ufs/ffs/fs.h>
11
12#include <err.h>
13#include <fcntl.h>
14#include <stdlib.h>
15#include <string.h>
16#include <stdio.h>
17#include <unistd.h>
18
19/*
20 * Possible superblock locations ordered from most to least likely.
21 */
22static int sblock_try[] = SBLOCKSEARCH;
23
24static void
25usage(void)
26{
27	(void)fprintf(stderr, "usage: zapsb special_device\n");
28	exit(1);
29}
30
31int
32main(int argc, char *argv[])
33{
34	char *fs, sblock[SBLOCKSIZE];
35	struct fs *sbp;
36	int i, fd;
37
38	if (argc != 2)
39		usage();
40
41	fs = *++argv;
42
43	/* get the superblock. */
44	if ((fd = open(fs, O_RDWR, 0)) < 0)
45		err(1, "%s", fs);
46	for (i = 0; sblock_try[i] != -1; i++) {
47		if (lseek(fd, (off_t)(sblock_try[i]), SEEK_SET) < 0)
48			err(1, "%s", fs);
49		if (read(fd, sblock, sizeof(sblock)) != sizeof(sblock))
50			errx(1, "%s: can't read superblock", fs);
51		sbp = (struct fs *)sblock;
52		if ((sbp->fs_magic == FS_UFS1_MAGIC ||
53		     (sbp->fs_magic == FS_UFS2_MAGIC &&
54		      sbp->fs_sblockloc == sblock_try[i])) &&
55		    sbp->fs_bsize <= MAXBSIZE &&
56		    sbp->fs_bsize >= (int)sizeof(struct fs))
57			break;
58	}
59	if (sblock_try[i] == -1) {
60		fprintf(stderr, "Cannot find file system superblock\n");
61		exit(2);
62	}
63	if ((sbp->fs_metackhash & CK_SUPERBLOCK) == 0) {
64		fprintf(stderr, "file system superblock has no check hash\n");
65		exit(3);
66	}
67	printf("zeroing superblock checksum at location %d\n", sblock_try[i]);
68	sbp->fs_ckhash = 0;
69	if (lseek(fd, (off_t)(sblock_try[i]), SEEK_SET) < 0)
70		err(1, "%s", fs);
71	if (write(fd, sblock, sizeof(sblock)) != sizeof(sblock))
72		errx(1, "%s: can't write superblock", fs);
73	(void)close(fd);
74	exit(0);
75}
76