#include <sys/mman.h>

#include <err.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>

int
main(void)
{
	int flag;
	int npgalloc = 33, npggood = 32, npgbad = npgalloc - npggood;
	int pagesize = getpagesize();
	void *p = NULL;
	ssize_t nwrit;

	/* Clear O_APPEND.  */
	if ((flag = fcntl(STDOUT_FILENO, F_GETFL)) == -1)
		err(1, "fcntl(F_GETFL)");
	flag &= ~O_APPEND;
	if (fcntl(STDOUT_FILENO, F_SETFL, flag) == -1)
		err(1, "fcntl(F_SETFL)");

	/* Allocate a batch of pages.  */
	if ((p = mmap(NULL, npgalloc*pagesize, PROT_READ|PROT_WRITE,
		    MAP_ANON|MAP_PRIVATE, -1, 0)) == MAP_FAILED)
		err(1, "mmap");

	/* Write zeros.  */
	if (lseek(STDOUT_FILENO, 0, SEEK_SET) == -1)
		warn("lseek");
	if ((nwrit = write(STDOUT_FILENO, p, npgalloc*pagesize)) == -1)
		err(1, "write");
	warnx("nwrit=%zd", nwrit);

	/* Replace by nonzero.  */
	memset(p, 0xc5, npgalloc*pagesize);

	/* Render the last chunk of pages unwritable.  */
#if 1
	if (mprotect(p + npggood*pagesize, npgbad*pagesize, PROT_NONE) == -1)
		err(1, "mprotect");
#elif 0
	if (mprotect(p + npggood*pagesize, npgbad*pagesize, PROT_WRITE) == -1)
		err(1, "mprotect");
#else
	if (munmap(p + npggood*pagesize, npgbad*pagesize) == -1)
		err(1, "munmap");
#endif

	/* Write it out.  */
	if (lseek(STDOUT_FILENO, 0, SEEK_SET) == -1)
		warn("lseek");
	if ((nwrit = write(STDOUT_FILENO, p, npgalloc*pagesize)) == -1)
		err(1, "write");
	warnx("nwrit=%zd", nwrit);

	return 0;
}