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/*
* swap-offset.c
*
* This program determines the location of the swap offset for given swap file.
*
* Copyright (C) 2006 Luca Tettamanti <kronos.it@gmail.com>
*
* This file is released under the GPLv2.
*
*/
#include "config.h"
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <linux/fs.h>
#include <errno.h>
#define SWAP_SIG "SWAPSPACE2"
#define SWAP_SIG_SIZE 10
int main(int argc, char **argv)
{
unsigned int block, last_block, first_block, blocks_per_page;
unsigned int offset;
int size, blk_size;
int fd;
unsigned int i;
ssize_t ret;
struct stat stat;
unsigned char buf[SWAP_SIG_SIZE];
int err = 0;
int const page_size = getpagesize();
if (argc < 2) {
fprintf(stderr, "Usage: swap-offset <file_name>\n");
return EINVAL;
}
fd = open(argv[1], O_RDONLY);
if (fd < 0) {
err = errno;
perror("open()");
return err;
}
if (fstat(fd, &stat)) {
err = errno;
perror("fstat()");
goto out;
}
if (!S_ISREG(stat.st_mode)) {
fprintf(stderr, "Not a regular file\n");
err = EINVAL;
goto out;
}
/* Check swap signature */
if (lseek(fd, page_size - SWAP_SIG_SIZE, SEEK_SET) < 0) {
err = errno;
perror("lseek()");
goto out;
}
ret = read(fd, buf, SWAP_SIG_SIZE);
if (ret < 0) {
err = errno;
perror("read()");
goto out;
} else if (ret < SWAP_SIG_SIZE) {
fprintf(stderr, "Failed to read swap signature: file is too short.\n");
err = EINVAL;
goto out;
}
if (memcmp(buf, SWAP_SIG, SWAP_SIG_SIZE)) {
fprintf(stderr, "Swap signature not found.\n");
err = EINVAL;
goto out;
}
if (ioctl(fd, FIGETBSZ, &blk_size)) {
err = errno;
perror("ioctl(FIGETBSZ) failed");
goto out;
}
blocks_per_page = page_size / blk_size;
/* Check that the header is contiguous */
last_block = 0;
first_block = 0;
size = 0;
for (i = 0; i < blocks_per_page; i++) {
block = i;
if (ioctl(fd, FIBMAP, &block)) {
err = errno;
perror("ioctl(FIBMAP) failed");
goto out;
}
if (last_block && block != last_block + 1)
break;
if (!first_block)
first_block = block;
size += blk_size;
last_block = block;
}
if (size < page_size) {
fprintf(stderr, "Swapfile header is not contiguous and cannot "
"be used for suspension.\n");
err = EINVAL;
} else {
offset = (unsigned long long)first_block * blk_size / page_size;
printf("resume offset = %u\n", offset);
}
out:
close(fd);
return err;
}
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