cow

Documentation

Overview

Package cow materializes a file as a copy-on-write copy of another.

On filesystems that support block-level reflink (APFS on macOS, btrfs/xfs-with-reflink/bcachefs on Linux) the clone is near-instant and uses zero extra storage until one side diverges. On filesystems that don't support it — ext4, tmpfs, NFS — Clone falls back to a sparse-preserving byte copy.

The primary consumer is machine/oci, which needs every Machine to get its own writable disk without mutating the shared pull cache.

Index

• func Clone(src, dst string) error

Functions

func Clone

func Clone(src, dst string) error

Clone materializes dst as a copy of src using the fastest path the filesystem supports. If src and dst resolve to the same path, Clone is a no-op. If dst exists, it is replaced.

The parent directory of dst must already exist.