The new 'unique' API allows listing all unique field values that a field
specified by a field name can take in all entries of the journal. This
allows answering queries such as "What units logged to the journal?",
"What hosts have logged into the journal?", "Which boot IDs have logged
into the journal?".
Ultimately this allows implementation of tools similar to lastlog based
on journal data.
Note that listing these field values will not work for journal files
created with older journald, as the field values are not indexed in
older files.
instead of having one simple per-file cache implement an more
comprehensive one that works for multiple files and can actually
maintain multiple maps per file and per object type.
This adds forward-secure authentication of journal files. This patch
includes key generation as well as tagging of journal files,
Verification of journal files will be added in a later patch.
The default of 2047 hash table entries turned out to result in way too
many collisions for bigger files, hence scale the hash table size by the
estimated maximum file size.
we now can take multiple matches, and they will apply as AND if they
apply to different fields and OR if they apply to the same fields. Also,
terms of this kind can be combined with an overreaching OR.
