ssize_t      /* Read "n" bytes from a descriptor. */
readn(int fd, void *vptr, size_t n)
{
 size_t nleft;
 ssize_t nread;
 char *ptr;

ptr = vptr;
 nleft = n;
 while (nleft > 0) {
  if ( (nread = read(fd, ptr, nleft)) < 0) {
   if (errno == EINTR)
    nread = 0;  /* and call read() again */
   else
    return(-1);
  } else if (nread == 0)
   break;    /* EOF */

nleft -= nread;
  ptr   += nread;
 }
 return(n - nleft);  /* return >= 0 */
}

ssize_t      /* Write "n" bytes to a descriptor. */
writen(int fd, const void *vptr, size_t n)
{
 size_t  nleft;
 ssize_t  nwritten;
 const char *ptr;

ptr = vptr;
 nleft = n;
 while (nleft > 0) {
  if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
   if (nwritten < 0 && errno == EINTR)
    nwritten = 0;  /* and call write() again */
   else
    return(-1);   /* error */
  }

nleft -= nwritten;
  ptr   += nwritten;
 }
 return(n);
}