nfs_halfpage

nfs_halfpage.c

/* $Id: nfs_halfpage.c,v 1.2 2017/07/23 09:36:23 kostik Exp kostik $ */

#include <sys/fcntl.h>
#include <sys/mman.h>
#include <err.h>
#include <unistd.h>

int
main(int argc __unused, char *argv[])
{
	char *m;
	int error, fd, pgsz, sz;

	pgsz = getpagesize();
	fd = open(argv[1], O_RDWR | O_CREAT | O_TRUNC, 0666);
	if (fd == -1)
		err(1, "open %s", argv[1]);
	sz = pgsz / 4;
	error = lseek(fd, sz, SEEK_SET);
	if (error == -1)
		err(1, "lseek");
	error = write(fd, "a", 1);
	if (error == -1)
		err(1, "write");
	else if (error != 1)
		errx(1, "short write");
	m = mmap(NULL, sz + 1, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
	if (m == MAP_FAILED)
		err(1, "mmap");
	m[0] = 'x';
}

Run this program with the argument a filename to be created on an nfs mount, then reboot the machine. It should loop syncing vnodes and buffers.