/*
 * compile with -DDO_FSYNC=1 and then with -DDO_FSYNC=0
 */
#include <sys/types.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#if !defined(DO_FSYNC)
# error "You must define DO_FSYNC"
#endif

#define MYBUFSIZ BUFSIZ
#define BYTES_TO_WRITE (32*1024*1024) /* 32MB */

int main(int argc, char *argv[])
{
	int fd, rc, i;
	char buf[MYBUFSIZ] = { '\0', };

	fd = open("testfile", O_WRONLY|O_CREAT, 0600);
	if (fd < 0) {
		perror("open");
		exit(1);
	}

	for (i = 0; i < (BYTES_TO_WRITE/MYBUFSIZ); i++) {
		rc = lseek(fd, 0, SEEK_SET);
		if (rc < 0) {
			perror("lseek");
			exit(1);
		}
		rc = write(fd, buf, sizeof(buf));
		if (rc < 0) {
			perror("write");
			exit(1);
		}
#if DO_FSYNC
		fdatasync(fd);
		if (rc < 0) {
			perror("fdatasync");
			exit(1);
		}
#endif
	} 
}