send_io

static VALUE
unix_send_io(VALUE sock, VALUE val)
{
#if defined(HAVE_SENDMSG) && (FD_PASSING_BY_MSG_CONTROL || FD_PASSING_BY_MSG_ACCRIGHTS)
    int fd;
    rb_io_t *fptr;
    struct iomsg_arg arg;
    struct iovec vec[1];
    char buf[1];

#if FD_PASSING_BY_MSG_CONTROL
    struct {
        struct cmsghdr hdr;
        char pad[8+sizeof(int)+8];
    } cmsg;
#endif

    if (rb_obj_is_kind_of(val, rb_cIO)) {
        rb_io_t *valfptr;
        GetOpenFile(val, valfptr);
        fd = valfptr->fd;
    }
    else if (FIXNUM_P(val)) {
        fd = FIX2INT(val);
    }
    else {
        rb_raise(rb_eTypeError, "neither IO nor file descriptor");
    }

    GetOpenFile(sock, fptr);

    arg.msg.msg_name = NULL;
    arg.msg.msg_namelen = 0;

    /* Linux and Solaris doesn't work if msg_iov is NULL. */
    buf[0] = '\0';
    vec[0].iov_base = buf;
    vec[0].iov_len = 1;
    arg.msg.msg_iov = vec;
    arg.msg.msg_iovlen = 1;

#if FD_PASSING_BY_MSG_CONTROL
    arg.msg.msg_control = (caddr_t)&cmsg;
    arg.msg.msg_controllen = CMSG_LEN(sizeof(int));
    arg.msg.msg_flags = 0;
    MEMZERO((char*)&cmsg, char, sizeof(cmsg));
    cmsg.hdr.cmsg_len = CMSG_LEN(sizeof(int));
    cmsg.hdr.cmsg_level = SOL_SOCKET;
    cmsg.hdr.cmsg_type = SCM_RIGHTS;
    *(int *)CMSG_DATA(&cmsg.hdr) = fd;
#else
    arg.msg.msg_accrights = (caddr_t)&fd;
    arg.msg.msg_accrightslen = sizeof(fd);
#endif

    arg.fd = fptr->fd;
    rb_thread_fd_writable(arg.fd);
    if ((int)BLOCKING_REGION(sendmsg_blocking, &arg) == -1)
        rb_sys_fail("sendmsg(2)");

    return Qnil;
#else
    rb_notimplement();
    return Qnil;                /* not reached */
#endif
}