Reference environment: macOS 26.7.1, build 25G241, arm64, local APFS. Consistent capture of a source file We are evaluating NSFileCoordinator with the forUploading and withoutChanges options for a single regular file. Does the resulting snapshot guarantee byte contents corresponding to a single point in time, even if another process writes during capture without file coordination, using write/pwrite or a shared writable memory mapping? We need to establish the scope, conditions, and limitations of this guarantee. We do not require capturing an editor’s unsaved changes or application-level database consistency. If any of these concurrent writing methods are not covered, please identify them explicitly. Durability of the final filename after a rename We are evaluating the following sequence: a verified temporary file has successfully completed strong synchronization, and is then renamed using renameatx_np with RENAME_EXCL. The temporary and final names are in the same directory on the same volume. Next, fsync_volume_np is called with SYNC_VOLUME_FULLSYNC and SYNC_VOLUME_WAIT. Under what conditions does a successful return confirm that the final filename and its association with the prepared file contents will survive a system crash or power loss? We also need clarification on whether all relevant data and metadata write errors are propagated to the caller, or whether an earlier error might remain unreported by this operation. Please provide the documented scope and limitations for this environment.

macOS APFS: NSFileCoordinator snapshot consistency and renameatx_np durability guarantees

Reference environment: macOS 26.7.1, build 25G241, arm64, local APFS.

Consistent capture of a source file

We are evaluating NSFileCoordinator with the forUploading and withoutChanges options for a single regular file.

Does the resulting snapshot guarantee byte contents corresponding to a single point in time, even if another process writes during capture without file coordination, using write/pwrite or a shared writable memory mapping?

We need to establish the scope, conditions, and limitations of this guarantee. We do not require capturing an editor’s unsaved changes or application-level database consistency. If any of these concurrent writing methods are not covered, please identify them explicitly.

Durability of the final filename after a rename

We are evaluating the following sequence: a verified temporary file has successfully completed strong synchronization, and is then renamed using renameatx_np with RENAME_EXCL. The temporary and final names are in the same directory on the same volume.

Next, fsync_volume_np is called with SYNC_VOLUME_FULLSYNC and SYNC_VOLUME_WAIT.

Under what conditions does a successful return confirm that the final filename and its association with the prepared file contents will survive a system crash or power loss?

We also need clarification on whether all relevant data and metadata write errors are propagated to the caller, or whether an earlier error might remain unreported by this operation. Please provide the documented scope and limitations for this environment.