Sluggish attempt to test how Rust binds to C code

simplecow.rs

/* automatically generated by rust-bindgen */

// sources: https://raw.github.com/vi/forsnapshotfs/master/simplecow.h https://raw.github.com/vi/forsnapshotfs/master/simplecow.c

use std::libc::*;

//pub type backing_read_t = *u8;
pub type Struct_simplecow = c_void;

#[link_args = "-lsimplecow"]
pub extern "C" {
    fn simplecow_write(cow: *mut Struct_simplecow, offset: c_longlong,
                       size: c_int, buf: *c_schar) -> c_int;
    fn simplecow_read(cow: *mut Struct_simplecow, offset: c_longlong,
                      size: c_int, buf: *mut c_schar) -> c_int;
    fn simplecow_create(br: c_void /* what to write here ? */, usr: *mut c_void) ->
     *mut Struct_simplecow;
    fn simplecow_destroy(cow: *mut Struct_simplecow);
}

// stub reading function that just fills the buffer with \x38.
fn myread(usr:c_void, offset: c_longlong, size:c_int,  buf:c_schar) -> c_int {
    unsafe {
        std::ptr::set_memory(buf as (*mut u8), 0x38, size as uint);
    }
    size
}

//typedef int (*backing_read_t)(void* usr, long long int offset, int size, char* buf);

fn main() {
    //let mut q : Struct_simplecow = 
    //    simplecow_create(myread as c_void /* what to write here ?*/, std::ptr::mut_null());
    
    //let mut q : Struct_simplecow = std::ptr::mut_null(); // also fails

    let mut q : (*mut Struct_simplecow);
    
    let mut buf  : [i8, .. 3]  = [4,5,6];
    //simplecow_read(q, 111, 3, buf as (*mut i8)); // also fails...
    println(fmt!("%02x %02x %02x\n", buf[0] as uint, buf[1] as uint, buf[2] as uint));
}