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/* In OpenBSD, if you write to a file, another process doesn't see it
* in its mmap. Returns with exit status 0 if that is the case, 1 if
* it's coherent, and other if there's a problem. */
#include <err.h>
#include <sys/mman.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#define DATA "coherent.mmap"
int main(int argc, char *argv[])
{
int tochild[2], toparent[2];
int fd;
volatile unsigned char *map;
unsigned char *page;
const char *fname = argv[1];
char c = 0;
if (pipe(tochild) != 0 || pipe(toparent) != 0)
err(2, "Creating pipe");
if (!fname)
fname = DATA;
fd = open(fname, O_RDWR|O_CREAT|O_TRUNC, 0600);
if (fd < 0)
err(2, "opening %s", fname);
unlink(fname);
switch (fork()) {
case -1:
err(2, "Fork");
case 0:
close(tochild[1]);
close(toparent[0]);
/* Wait for parent to create file. */
if (read(tochild[0], &c, 1) != 1)
err(2, "reading from parent");
/* Alter first byte. */
pwrite(fd, &c, 1, 0);
if (write(toparent[1], &c, 1) != 1)
err(2, "writing to parent");
exit(0);
default:
close(tochild[0]);
close(toparent[1]);
/* Create a file and mmap it. */
page = malloc(getpagesize());
memset(page, 0x42, getpagesize());
if (write(fd, page, getpagesize()) != getpagesize())
err(2, "writing first page");
map = mmap(NULL, getpagesize(), PROT_READ|PROT_WRITE,
MAP_SHARED, fd, 0);
if (map == MAP_FAILED)
err(2, "mapping file");
if (*map != 0x42)
errx(2, "first byte isn't 0x42!");
/* Tell child to alter file. */
if (write(tochild[1], &c, 1) != 1)
err(2, "writing to child");
if (read(toparent[0], &c, 1) != 1)
err(2, "reading from child");
if (*map)
errx(0, "mmap incoherent: first byte isn't 0.");
exit(1);
}
}
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