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#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include "ext4.h"
#include "ext4_utils.h"
#define SB_OFFSET 1024
int main(int argc, char *argv[])
{
char me[] = "corrupt_gdt_free_blocks";
int fd;
int block_size;
int num_bgs;
int i;
struct ext4_super_block sb;
struct ext2_group_desc gd;
if (argc != 2) {
fprintf(stderr, "%s: Usage: %s <ext4_block_device>\n", me, me);
exit(1);
}
fd = open(argv[1], O_RDWR);
if (fd < 0) {
fprintf(stderr, "%s: Cannot open block device %s\n", me, argv[1]);
exit(1);
}
if (lseek(fd, SB_OFFSET, SEEK_SET) == -1) {
fprintf(stderr, "%s: Cannot lseek to superblock to read\n", me);
exit(1);
}
if (read(fd, &sb, sizeof(sb)) != sizeof(sb)) {
fprintf(stderr, "%s: Cannot read superblock\n", me);
exit(1);
}
if (sb.s_magic != 0xEF53) {
fprintf(stderr, "%s: invalid superblock magic\n", me);
exit(1);
}
/* Make sure the block size is 2K or 4K */
if ((sb.s_log_block_size != 1) && (sb.s_log_block_size != 2)) {
fprintf(stderr, "%s: block size not 2K or 4K\n", me);
exit(1);
}
block_size = 1 << (10 + sb.s_log_block_size);
num_bgs = DIV_ROUND_UP(sb.s_blocks_count_lo, sb.s_blocks_per_group);
if (sb.s_desc_size != sizeof(struct ext2_group_desc)) {
fprintf(stderr, "%s: Can't handle block group descriptor size of %d\n",
me, sb.s_desc_size);
exit(1);
}
/* read first block group descriptor, decrement free block count, and
* write it back out
*/
if (lseek(fd, block_size, SEEK_SET) == -1) {
fprintf(stderr, "%s: Cannot lseek to block group descriptor table to read\n", me);
exit(1);
}
/* Read in block group descriptors till we read one that has at least one free block */
for (i=0; i < num_bgs; i++) {
if (read(fd, &gd, sizeof(gd)) != sizeof(gd)) {
fprintf(stderr, "%s: Cannot read group descriptor %d\n", me, i);
exit(1);
}
if (gd.bg_free_blocks_count) {
break;
}
}
gd.bg_free_blocks_count--;
if (lseek(fd, -sizeof(gd), SEEK_CUR) == -1) {
fprintf(stderr, "%s: Cannot lseek to block group descriptor table to write\n", me);
exit(1);
}
if (write(fd, &gd, sizeof(gd)) != sizeof(gd)) {
fprintf(stderr, "%s: Cannot write modified group descriptor\n", me);
exit(1);
}
close(fd);
return 0;
}
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