nonblock=

static VALUE
rb_io_nonblock_set(VALUE io, VALUE nb)
{
    rb_io_t *fptr;
    GetOpenFile(io, fptr);
    if (RTEST(nb))
        rb_io_set_nonblock(fptr);
    else
        io_nonblock_set(fptr->fd, io_nonblock_mode(fptr->fd), RTEST(nb));
    return io;
}