feat(cli): add --cow / --no-cow flag#3740
Merged
Merged
Conversation
Introduce a CowPolicy enum on `fast_io` and a NoCowPlatformCopy adapter that forces every whole-file copy through the portable std::fs::copy fallback. Wire `--cow` (default Auto) and `--no-cow` (Disabled) through the CLI parser, ClientConfig, and `build_local_copy_options`, swapping the platform-copy strategy when reflinks are disabled. Useful for benchmarking, diagnostics, and downstream tooling that does not handle FICLONE/copy_file_range/clonefile/ReFS reflinks.
oferchen
added a commit
that referenced
this pull request
May 18, 2026
Introduce a CowPolicy enum on `fast_io` and a NoCowPlatformCopy adapter that forces every whole-file copy through the portable std::fs::copy fallback. Wire `--cow` (default Auto) and `--no-cow` (Disabled) through the CLI parser, ClientConfig, and `build_local_copy_options`, swapping the platform-copy strategy when reflinks are disabled. Useful for benchmarking, diagnostics, and downstream tooling that does not handle FICLONE/copy_file_range/clonefile/ReFS reflinks.
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Summary
CowPolicyenum (Autodefault,Disabled) and aNoCowPlatformCopyadapter onfast_iothat forces every whole-file copy throughstd::fs::copy, reportingCopyMethod::StandardCopyso downstream fast paths (such as the macOS clonefile shortcut) skip the reflink branch.--cow/--no-cowclap flag pair (mirroring--io-uring/--no-io-uring) withoverrides_withso the last flag wins, and surface them in the help text andSUPPORTED_OPTIONS_LIST.ParsedArgs, the drive config inputs,ClientConfigBuilder, andbuild_local_copy_options, swapping the platform-copy strategy onLocalCopyOptionswhen--no-cowis in effect.--no-cowis useful for benchmarking, diagnostics, and downstream tooling that does not handle FICLONE /copy_file_range/ clonefile / ReFS reflinks. CoW remains opt-out only - the default--cowmatches existing behaviour.Test plan
cargo nextest run -p fast_io --all-features -E 'test(no_cow)'cargo nextest run -p fast_io --all-features -E 'test(cow_policy)'cargo nextest run -p oc-rsync-cli --all-features -E 'test(cow)'cargo nextest run -p core --all-features -E 'test(cow_policy)'