I would assume cp uses ioctl (with atomic copies of individual files on filesystems that support CoW like APFS and BTRFS), whereas sqlite probably uses mmap?
I was trying to find evidence that reflink copies are atomic and could not and LLMs seem to think they are not. So at best may be a btrfs only feature?
> Clones are atomic with regards to concurrent writes, so no locks need to be taken to obtain a consistent cloned copy.
I'm not aware of any of the filesystems that use it (Btrfs, XFS, Bcachefs, ZFS) that deviate from expected atomic behavior, at least with single files being the atom in question for `FICLONE` operation.
