hesela.devMetadata-only copy-up
Metadata-only copy-up is an OverlayFS feature that creates upper-layer metadata for a regular file while retaining its data in a lower layer.
When enabled, metacopy can avoid copying payload for a chmod operation. [1] For a file still in metadata-only state, a writable open requests data copy-up before an application write is needed; successful data copy-up removes the metacopy marker. Truncation does not promise preservation of the old payload. [2]
Recovery implication: an upper-tree-only backup can omit required lower data. Retain coherent layer dependencies or capture the intended merged content with an explicit consistency policy. This is an architectural inference, not an observed restore failure. [1]
Relations
- related
- OverlayFS, Copy-up (OverlayFS)
Advantages
- Can defer payload transfer for metadata-only changes.
Limitations
- Feature state is configurable; metacopy is not authentication or a durability guarantee.
- Linux warns against metacopy with untrusted layer trees; fs-verity arrangements have separate trust requirements.
Citations
- Linux 6.12: Overlay Filesystem, non-directories and metadata-only copy-up
- Linux v6.12: OverlayFS copy-up eligibility, data transfer and truncation
Sources & caveats
- Source review of Linux 6.12 documentation and implementation; no mounted-overlay, restore or crash experiment.