#include <sys/mman.h>
#include <sys/wait.h>

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

#define NENTRIES        70000

int
main(void)
{
        char *base;
        size_t i, pgsz;
        pid_t pid;

        pgsz = getpagesize();
        base = mmap(NULL, NENTRIES * pgsz, PROT_READ | PROT_WRITE,
            MAP_ANON | MAP_PRIVATE, -1, 0);
        if (base == MAP_FAILED)
                err(1, "mmap");
        /* Alternate protections so each page is its own map entry. */
        for (i = 1; i < NENTRIES; i += 2)
                if (mprotect(base + i * pgsz, pgsz, PROT_READ) != 0)
                        err(1, "mprotect");
        pid = fork();
        if (pid == -1)
                err(1, "fork");
        if (pid == 0) {
                /* Make sure the child faults at least once. */
                base[0] = 1;
                _exit(0);
        }
        if (waitpid(pid, NULL, 0) == -1)
                err(1, "waitpid");
        return (0);
}