A disruptive chunkd on-disk file format change was just pushed to hail.git. It is a minor format update, but it is incompatible. chunkd v0.8+ objects are now binary-incompatible with the just-released chunkd v0.7.
The update adds a magic number and object size to the on-disk object header (struct be_fs_obj_hdr), plus some reserved space for future additions.
The magic number and object size add easy (and CPU-inexpensive) sanity checks to the object I/O code. The object size field is largely redundant, intended mainly for disaster recovery. However, storing the object size enables the file format to support multiple objects inside a single POSIX filesystem file.
Hopefully this means implementing an APPEND operation in chunkd is now feasible. But if APPEND falls through, these two new be_fs_obj_hdr members retain some utility anyway.
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