Adding [--repair] option for cephfs-journal-tool make it can recover all journal as much as possible.
As described in the document if a journal is damaged or for any reason an MDS is incapable of replaying it, attempt to recover what file metadata we can like so:
"cephfs-journal-tool event recover_dentries summary". I found a risk when research related code rencently which may lost journal log if it's damaged.The worse
case is if the length of journal is corrupt we may lost many journal.
Of course if a journal data is corrupt we can throw it away, but if only the length or trailling is corrupt we should repair it as much as possible, in case of losting event.