util-linux/disk-utils/mkswap.c

/*
 * mkswap.c - set up a linux swap device
 *
 * (C) 1991 Linus Torvalds. This file may be redistributed as per
 * the Linux copyright.
 */

/*
 * 20.12.91  -	time began. Got VM working yesterday by doing this by hand.
 *
 * Usuage: mkswap [-c] device [size-in-blocks]
 *
 *	-c for readablility checking (use it unless you are SURE!)
 *
 * The device may be a block device or a image of one, but this isn't
 * enforced (but it's not much fun on a character device :-).
 *
 * Patches from jaggy@purplet.demon.co.uk (Mike Jagdis) to make the
 * size-in-blocks parameter optional added Wed Feb  8 10:33:43 1995.
 */

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/stat.h>

#include <linux/mm.h>

#ifndef __GNUC__
#error "needs gcc for the bitop-__asm__'s"
#endif

#ifndef __linux__
#define volatile
#endif

#define TEST_BUFFER_PAGES 8

static char * program_name = "mkswap";
static char * device_name = NULL;
static int DEV = -1;
static long PAGES = 0;
static int check = 0;
static int badpages = 0;

static char signature_page[PAGE_SIZE];

#define bitop(name,op) \
static inline int name(char * addr,unsigned int nr) \
{ \
int __res; \
__asm__ __volatile__("bt" op " %1,%2; adcl $0,%0" \
:"=g" (__res) \
:"r" (nr),"m" (*(addr)),"0" (0)); \
return __res; \
}

bitop(bit,"")
bitop(setbit,"s")
bitop(clrbit,"r")

/*
 * Volatile to let gcc know that this doesn't return. When trying
 * to compile this under minix, volatile gives a warning, as
 * exit() isn't defined as volatile under minix.
 */
volatile void fatal_error(const char * fmt_string)
{
	fprintf(stderr,fmt_string,program_name,device_name);
	exit(1);
}

#define usage() fatal_error("Usage: %s [-c] /dev/name [blocks]\n")
#define die(str) fatal_error("%s: " str "\n")

void check_blocks(void)
{
	unsigned int current_page;
	int do_seek = 1;
	static char buffer[PAGE_SIZE];

	current_page = 0;
	while (current_page < PAGES) {
		if (!check) {
			setbit(signature_page,current_page++);
			continue;
		}
		if (do_seek && lseek(DEV,current_page*PAGE_SIZE,SEEK_SET) !=
		current_page*PAGE_SIZE)
			die("seek failed in check_blocks");
		if (do_seek = (PAGE_SIZE != read(DEV, buffer, PAGE_SIZE))) {
			clrbit(signature_page,current_page++);
			badpages++;
			continue;
		}
		setbit(signature_page,current_page++);
	}
	if (badpages)
		printf("%d bad page%s\n",badpages,(badpages>1)?"s":"");
}

static long valid_offset (int fd, int offset)
{
	char ch;

	if (lseek (fd, offset, 0) < 0)
		return 0;
	if (read (fd, &ch, 1) < 1)
		return 0;
	return 1;
}

static int count_blocks (int fd)
{
	int high, low;

	low = 0;
	for (high = 1; valid_offset (fd, high); high *= 2)
		low = high;
	while (low < high - 1)
	{
		const int mid = (low + high) / 2;

		if (valid_offset (fd, mid))
			low = mid;
		else
			high = mid;
	}
	valid_offset (fd, 0);
	return (low + 1);
}

static int get_size(const char  *file)
{
	int	fd;
	int	size;

	fd = open(file, O_RDWR);
	if (fd < 0) {
		perror(file);
		exit(1);
	}
	if (ioctl(fd, BLKGETSIZE, &size) >= 0) {
		close(fd);
		return (size * 512);
	}
		
	size = count_blocks(fd);
	close(fd);
	return size;
}

int main(int argc, char ** argv)
{
	char * tmp;
	struct stat statbuf;
	int goodpages;

	memset(signature_page,0,PAGE_SIZE);
	if (argc && *argv)
		program_name = *argv;
	while (argc-- > 1) {
		argv++;
		if (argv[0][0] != '-')
			if (device_name) {
				PAGES = strtol(argv[0],&tmp,0)>>2;
				if (*tmp)
					usage();
			} else
				device_name = argv[0];
		else while (*++argv[0])
			switch (argv[0][0]) {
				case 'c': check=1; break;
				default: usage();
			}
	}
	if (device_name && !PAGES) {
		PAGES = get_size(device_name) / PAGE_SIZE;
	}
	if (!device_name || PAGES<10)
		usage();
	if (PAGES > 32688) /* 130752 blocks */
	        PAGES=32688;
#if 0
	if (PAGES > 32768)
		PAGES=32768;
#endif
	DEV = open(device_name,O_RDWR);
	if (DEV < 0 || fstat(DEV, &statbuf) < 0) {
		perror(device_name);
		exit(1);
	}
	if (!S_ISBLK(statbuf.st_mode))
		check=0;
	else if (statbuf.st_rdev == 0x0300 || statbuf.st_rdev == 0x0340)
		die("Will not try to make swapdevice on '%s'");
	check_blocks();
	if (!clrbit(signature_page,0))
		die("fatal: first page unreadable");
	goodpages = PAGES - badpages - 1;
	if (!goodpages)
		die("Unable to set up swap-space: unreadable");
	printf("Setting up swapspace, size = %d bytes\n",goodpages*PAGE_SIZE);
	strncpy(signature_page+PAGE_SIZE-10,"SWAP-SPACE",10);
	if (lseek(DEV, 0, SEEK_SET))
		die("unable to rewind swap-device");
	if (PAGE_SIZE != write(DEV, signature_page, PAGE_SIZE))
		die("unable to write signature page");
	return 0;
}