Reflinking is a safe optimization whenever the source and destination are
regular, seekable files on a filesystem that supports cloning. Requiring each
caller to opt in through COPY_REFLINK adds flag plumbing without changing the
necessary fallback behavior.
Drop COPY_REFLINK, renumber the remaining flags, and have copy_bytes_full()
unconditionally try FICLONE or FICLONERANGE before entering its normal copy
loop. Isolate the clone attempt and its file-offset bookkeeping in a helper so
copy_bytes_full() only has to handle its cloned, unavailable, and error results.
A successful clone therefore completes in one operation, while an unsupported
or rejected clone falls back to progress-limited copy_file_range(), sendfile(),
or buffered copying. Keep the public reflink helpers for operations that
specifically require clone semantics.
Existing test-copy coverage exercises both bounded and unbounded regular-file
copies through copy_bytes_full().
Signed-off-by: Daan De Meyer <daan@amutable.com>
Daan De Meyer
5a12005c83