RFC: sfs file tree: store metadata in MP / version files

[irq0]

What needs to be done

Store metadata (e.g object id, mp id, commit time, owner) with the MP part / object version file in the SFS dir tree.

Why it needs to be done

It would help a fsck tool and a human debugging.

Design Space

Header / footer

Let file data start at a fixed offset. Append data after file data.

A fixed offset header needs to take alignment into account as SFS will never read it.

Can be implemented so that head -1 works.

XAttrs

Store everything in a single / separate xattrs.

xattrs have performance / overhead on the filesystem that needs to be taken into account. Backing up / copying the datastore may loose xattrs.

[tserong]

Is this intended to duplicate, supplement, or replace the metadata that's already present in the sqlite database?

[irq0]

Duplicate. Put all information necessary with the file to make it self describing

[tserong]

Seems reasonable, and definitely helpful to humans debugging.

For fsck it adds another thing to check: that file metadata matches db metadata :-P

[jhmarina]

This should be defined in an ADR