checkpoint a disk relation that prevents file regrowth
checkpoint a disk relation that prevents file regrowth

this could be useful for eventually proving a cleaner [update_fblock_d_ok].
however, it is a bit too restrictive right now due to inode number reuse.
one solution may be to add generation numbers to inodes (and it may be
possible to make generation #s purely ghost state).

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl