Search for ext2 superblock in...

Current version: e2sl-0.1.tar.gz, released on June 10th 2000

The Ext2 Superblock Locator can help you to find the superblock of your ext2 partition. I wrote this tool, because an unnamed OS installer screwed up the partition table of my harddisk. Of course, I had no idea on which exact block number the partition started.

This is a very simply tool with a simply user interface. It will compile on all Linux systems. If your system supports LFS, it will be automatically activated (this allows searching larger harddisks).

To use it, download the current tarball, unpack it, cd into the e2sl-x.x directory and run make.

NOTE: Manually changing the partition table is very risky. Never make a change to a partition table without backing it up on a disk. It will save both, your data and your day.

Sascha Schumann's homepage

File: /root/Apps/e2sl-0.1/ext2-superblock.c Page 1 of 3

#include #include #include #include #include #include #include #include

/* for struct ext2_super_block, EXT2_SUPER_MAGIC and EXT2_BLOCK_SIZE */ #include

#define BUFSIZE 512 #define CLEAR \

if (clear) { printf("\r"); clear = 0; }

static unsigned int heads = 240;

static unsigned int sectors_per_head = 63;

static char *block_verbose(unsigned long long i)

{

static char buf[512];

sprintf(buf, "cyl %llu, head %llu, sector %llu", i/(heads*sectors_per_head),

(i / sectors_per_head) % heads, i % sectors_per_head);

return buf;

}

static int work(const char *device, unsigned long long block, int freq)

{

char buf[BUFSIZE]; int fd;

struct ext2_super_block *blck = (struct ext2_super_block *) buf; int n;

int clear = 0; off_t offset;

fd = open(device, O_RDONLY);

if (fd == -1) {

fprintf(stderr, "cannot open %s: ", device); perror("open");

return (-1);

}

offset = lseek(fd, block * 512, SEEK_SET);

if (offset == (off_t) -1) { perror("lseek"); return (-1);

}

printf("seeked to offset %lld, wanted offset %llu (block %llu)\n", offset, block * 512, block);

while (1) {

n = read(fd, buf, BUFSIZE);

if (n == BUFSIZE && blck->s_magic == EXT2_SUPER_MAGIC) { unsigned long blck_size = EXT2_BLOCK_SIZE(blck);

/* filter out pseudo superblocks */

if (blck_size >= 1024 && blck_size <= 32768) { CLEAR;

printf("Found: block %llu (%s), %u blocks, %u free blocks, " "%u block size, %s\n",

File: /root/Apps/e2sl-0.1/ext2-superblock.c Page 2 of 3

block, block_verbose(block), blck->s_blocks_count, blck->s_free_blocks_count, EXT2_BLOCK_SIZE(blck),

ctime((const time_t *) &blck->s_mtime));

}

} else if (n <= 0) { perror( "read"); return (-1);

}

block++;

if ((block % freq) == 0) { CLEAR;

printf( "block %llu (%s)", block, block_verbose(block)); clear = 1;

fflush(stdout);

}

}

return (0);

}

static void usage(void)

{

printf("Ext2 Superblock Locator, version " VERSION

"\n"
"\n	Options:"
"\n	-d	device	Select which device to open [/dev/hda]"
"\n	-b	block	Which block to start with [0]"
"\n	-f	n	Update status every n blocks [5000]"
"\n"
"\nPlease		email bug reports to sascha@schumann.cx"
"\n"
"\n"
);
}

int main(int argc, char **argv)

{

int c;

int ret = 0;

char *device = strdup("/dev/hda"); unsigned long long block = 0;

int freq = 5000;

while ((c = getopt(argc, argv, "d:b:f:h")) != EOF) { switch(c) {

case 'd': free(device);

device = strdup(optarg); break;

case 'b':

block = strtoul(optarg, NULL, 10); break;

case 'f':

freq = strtol(optarg, NULL, 10); break;

default:

usage(); exit(1);

}

}

if (work(device, block, freq)) ret = 1;

File: /root/Apps/e2sl-0.1/ext2-superblock.c Page 3 of 3

free(device); exit(ret);

}