1 /* In OpenBSD, if you write to a file, another process doesn't see it
2 * in its mmap. Returns with exit status 0 if that is the case, 1 if
3 * it's coherent, and other if there's a problem. */
4 #include <err.h>
5 #include <sys/mman.h>
6 #include <unistd.h>
7 #include <sys/types.h>
8 #include <sys/stat.h>
9 #include <fcntl.h>
10 #include <stdlib.h>
11 #include <string.h>
12 #include <errno.h>
13
14 #define DATA "coherent.mmap"
15
main(int argc,char * argv[])16 int main(int argc, char *argv[])
17 {
18 int tochild[2], toparent[2];
19 int fd;
20 volatile unsigned char *map;
21 unsigned char *page;
22 const char *fname = argv[1];
23 char c = 0;
24
25 if (pipe(tochild) != 0 || pipe(toparent) != 0)
26 err(2, "Creating pipe");
27
28 if (!fname)
29 fname = DATA;
30
31 fd = open(fname, O_RDWR|O_CREAT|O_TRUNC, 0600);
32 if (fd < 0)
33 err(2, "opening %s", fname);
34 unlink(fname);
35
36 switch (fork()) {
37 case -1:
38 err(2, "Fork");
39 case 0:
40 close(tochild[1]);
41 close(toparent[0]);
42
43 /* Wait for parent to create file. */
44 if (read(tochild[0], &c, 1) != 1)
45 err(2, "reading from parent");
46
47 /* Alter first byte. */
48 pwrite(fd, &c, 1, 0);
49
50 if (write(toparent[1], &c, 1) != 1)
51 err(2, "writing to parent");
52 exit(0);
53
54 default:
55 close(tochild[0]);
56 close(toparent[1]);
57
58 /* Create a file and mmap it. */
59 page = malloc(getpagesize());
60 memset(page, 0x42, getpagesize());
61 if (write(fd, page, getpagesize()) != getpagesize())
62 err(2, "writing first page");
63 map = mmap(NULL, getpagesize(), PROT_READ|PROT_WRITE,
64 MAP_SHARED, fd, 0);
65 if (map == MAP_FAILED)
66 err(2, "mapping file");
67
68 if (*map != 0x42)
69 errx(2, "first byte isn't 0x42!");
70
71 /* Tell child to alter file. */
72 if (write(tochild[1], &c, 1) != 1)
73 err(2, "writing to child");
74
75 if (read(toparent[0], &c, 1) != 1)
76 err(2, "reading from child");
77
78 if (*map)
79 errx(0, "mmap incoherent: first byte isn't 0.");
80
81 exit(1);
82 }
83 }
84