lib/replace/test/incoherent_mmap.c

   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
  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 }