Function reflink

pub fn reflink<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> Result<()>

Copies a file using COW semantics.

For compatibility reasons with macos, the target file will be created using OpenOptions::create_new. If you want to overwrite existing files, make sure you manually delete the target file first if it exists.

use reflink;
match reflink::reflink("src.txt", "dest.txt") {
    Ok(()) => println!("file has been reflinked"),
    Err(e) => println!("error while reflinking: {:?}", e)
}

Implementation details per platform

Linux / Android

Uses ioctl_ficlone. Supported file systems include btrfs and XFS (and maybe more in the future).

OS X / ios

Uses clonefile library function. This is supported on OS X Version >=10.12 and iOS version >= 10.0 This will work on APFS partitions (which means most desktop systems are capable).

Windows

Uses ioctl FSCTL_DUPLICATE_EXTENTS_TO_FILE. Only supports ReFS on Windows Server. Important note: The windows implementation is currently untested and probably buggy. Contributions/testers with access to a Windows Server welcome.

Examples found in repository

examples/compare.rs (line 13)

fn main() {
    let mut base_file = fs::File::create("base.txt").unwrap();
    let mut src = io::repeat(65).take(100 * 1024 * 1024); // 100 MB
    io::copy(&mut src, &mut base_file).unwrap();

    let before_reflink = Instant::now();
    match reflink::reflink("base.txt", "reflinked.txt") {
        Ok(()) => {},
        Err(e) => {
            println!("Error during reflinking:\n{:?}", e);
            fs::remove_file("base.txt").unwrap();
            return;
        }
    };
    println!("Time to reflink: {:?}", Instant::now() - before_reflink);

    let before_copy = Instant::now();
    fs::copy("base.txt", "copied.txt").unwrap();
    println!("Time to copy: {:?}", Instant::now() - before_copy);

    fs::remove_file("base.txt").unwrap();
    fs::remove_file("reflinked.txt").unwrap();
    fs::remove_file("copied.txt").unwrap();
}