mkswap_u.c

#include <stdio.h>
#include <unistd.h>
#include <sys/swap.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <stdint.h>

/* XXX This needs to be obtained from kernel headers. See b/9336527 */
struct linux_swap_header {
	char            bootbits[1024]; /* Space for disklabel etc. */
	uint32_t        version;
	uint32_t        last_page;
	uint32_t        nr_badpages;
	unsigned char   sws_uuid[16];
	unsigned char   sws_volume[16];
	uint32_t        padding[117];
	uint32_t        badpages[1];
};

#define MAGIC_SWAP_HEADER     "SWAPSPACE2"
#define MAGIC_SWAP_HEADER_LEN 10
#define MIN_PAGES             10

int mkswap_main(int argc, char **argv) {
	int e = 0;
	int fd;
	ssize_t len;
	off_t swap_size;
	int pagesize;
	struct linux_swap_header sw_hdr;

	if(argc != 2) {
		fprintf(stderr, "Usage: %s <filename>\n", argv[0]);
		return -EINVAL;
	}

	fd = open(argv[1], O_WRONLY);
	if(fd == -1) {
		e = errno;
		fprintf(stderr, "Cannot open %s, %s\n", argv[1], strerror(e));
		return -e;
	}

	pagesize = getpagesize();
	/* Determine the length of the swap file */
	swap_size = lseek(fd, 0, SEEK_END);
	if(swap_size < MIN_PAGES * pagesize) {
		fprintf(stderr, "Swap file needs to be at least %dkB\n",
			(MIN_PAGES * pagesize) >> 10);
		e = -ENOSPC;
		goto err;
	}

	if(lseek(fd, 0, SEEK_SET)) {
		e = errno;
		fprintf(stderr, "Can't seek to the beginning of the file, %s\n", strerror(e));
		goto err;
	}

	memset(&sw_hdr, 0, sizeof(sw_hdr));
	sw_hdr.version = 1;
	sw_hdr.last_page = (swap_size / pagesize) - 1;
	len = write(fd, &sw_hdr, sizeof(sw_hdr));
	if(len != sizeof(sw_hdr)) {
		e = errno;
		fprintf(stderr, "Failed to write swap header into %s, %s\n", argv[1], strerror(e));
		goto err;
	}

	/* Write the magic header */
	if(lseek(fd, pagesize - MAGIC_SWAP_HEADER_LEN, SEEK_SET) < 0) {
		e = errno;
		fprintf(stderr, "Failed to seek into %s, %s\n", argv[1], strerror(e));
		goto err;
	}
	len = write(fd, MAGIC_SWAP_HEADER, MAGIC_SWAP_HEADER_LEN);
	if(len != MAGIC_SWAP_HEADER_LEN) {
		e = errno;
		fprintf(stderr, "Failed to write magic swap header into %s, %s\n", argv[1], strerror(e));
		goto err;
	}

	if(fsync(fd) < 0) {
		e = errno;
		fprintf(stderr, "Failed to sync %s, %s\n", argv[1], strerror(e));
		goto err;
	}

	return 0;

err:
	close(fd);
	return -e;
}