You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: getpty.rs
    path of file: ./repos/rustybox/libbb
    
    the code of the file until where you have to start completion: use crate::librb::size_t;
use libc;
use libc::open;
extern "C" {

  #[no_mangle]
  fn grantpt(__fd: libc::c_int) -> libc::c_int;
  #[no_mangle]
  fn unlockpt(__fd: libc::c_int) -> libc::c_int;
  #[no_mangle]
  fn ptsname_r(__fd: libc::c_int, __buf: *mut libc::c_char, __buflen: size_t) -> libc::c_int;

}

pub type C2RustUnnamed = libc::c_uint;
pub const GETPTY_BUFSIZE: C2RustUnnamed = 16;

/*
 * Busybox main internal header file
 *
 * Based in part on code from sash, Copyright (c) 1999 by David I. Bell
 * Permission has been granted to redistribute this code under GP
    
pub unsafe fn xgetpty(mut line: *mut libc::c_char) -> libc::c_int {
  let mut p: libc::c_int = 0; /* chmod+chown corresponding slave pty */
  p = open(b"/dev/ptmx\x00" as *const u8 as *const libc::c_char, 0o2i32); /* (what does this do?) */
  if p >= 0 {
    grantpt(p);
    unlockpt(p);
    /* find out the name of slave pty */
    if ptsname_r(p, line, (GETPTY_BUFSIZE as libc::c_int - 1i32) as size_t) != 0 {
      crate::libbb::perror_msg::bb_simple_perror_msg_and_die(
        b"ptsname error (is /dev/pts mounted?)\x00" as *const u8 as *const libc::c_char,
      );
    }
    *line.offset((GETPTY_BUFSIZE as libc::c_int - 1i32) as isize) = '\u{0}' as i32 as libc::c_char;
    return p;
  }
  /* FEATURE_DEVPTS */
  crate::libbb::verror_msg::bb_simple_error_msg_and_die(
    b"can\'t find free pty\x00" as *const u8 as *const libc::c_char,
  );
}