lib.rs

extern crate libc;
pub mod zc;

test.rs

#![feature(test)]
extern crate test;
extern crate zerocopy;
use zerocopy::zc::ZeroCopy;
use test::Bencher;
use std::io::prelude::*;
use std::fs::File;
#[bench]
fn zerocopy(b: &mut Bencher) {
    let mut src = File::open("/tmp/foo").unwrap();
    let mut dest = File::create("/tmp/foo.txt").unwrap();
    b.iter(|| {
        unsafe { src.copy_to_fd(&mut dest).unwrap() };
    });
    std::fs::remove_file("/tmp/foo.txt");

}
#[bench]
fn default(b: &mut Bencher) {
    let mut src = File::open("/tmp/foo").unwrap();
    let mut dest = File::create("/tmp/foo.txt").unwrap();
    let len = src.metadata().unwrap().len() as usize;

    b.iter(|| {
        ::std::io::copy(&mut src, &mut dest).unwrap();
        src.seek(::std::io::SeekFrom::Start(0));
        

    });
    std::fs::remove_file("/tmp/foo.txt");
}

zc.rs

use libc::{c_int, splice};
use std::os::unix::io::AsRawFd;
use std::io::Result;
use std::io::prelude::*;
const __NR_copy_file_range: ::libc::c_long = 326;

unsafe fn copy_file_range(fd_in: c_int, off_in: *mut ::libc::loff_t, fd_out: c_int, off_out: *mut ::libc::loff_t, len: usize, flags: u32) -> i64 {
    ::libc::syscall(__NR_copy_file_range, fd_in, off_in, fd_out, off_out, len, flags)
}
pub trait ZeroCopy<T> {
    unsafe fn copy_to_fd(&mut self, fd: &mut T) -> Result<u64>;
}

/*impl <T> ZeroCopy for T where T: AsRawFd + Read {
    unsafe fn copy_to_fd<FD: AsRawFd + Write>(&mut self, fd: &mut FD) -> Result<u64> { 
        let res = splice(0, ::std::ptr::null_mut(), fd.as_raw_fd(), ::std::ptr::null_mut(), 12, 0);
        Ok(res as u64)    
    }
}*/

impl ZeroCopy<::std::fs::File> for ::std::fs::File {
    unsafe fn copy_to_fd(&mut self, fd: &mut ::std::fs::File) -> Result<u64> {
        let len = fd.metadata()?.len() as usize;
        let bytes = copy_file_range(self.as_raw_fd(), ::std::ptr::null_mut(), fd.as_raw_fd(), ::std::ptr::null_mut(), len, 0);
        if bytes < 0 {
            Err(::std::io::Error::last_os_error())
        }
        else { Ok(bytes as u64) }

    }
}