ioctl, pass buffer address, howto?

[Neal Becker]

I need an ioctl call equivalent to this C code:

    my_struct s;
    s.p = p; << a pointer to an array of char
    s.image_size = image_size;
    return (ioctl(fd, xxx, &s));

I'm thinking to use python array for the array of char, but I don't see how
to put it's address into the structure.  Maybe ctypes is the answer?