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.
There's now sd_journal_new_directory() for watching specific journal
directories. This is exposed in journalctl -D.
sd_journal_wait() and sd_journal_process() now return whether changes in
the journal are invalidating or just appending.
We now create inotify kernel watches only when we actually need them
We finally got the OK from all contributors with non-trivial commits to
relicense systemd from GPL2+ to LGPL2.1+.
Some udev bits continue to be GPL2+ for now, but we are looking into
relicensing them too, to allow free copy/paste of all code within
systemd.
The bits that used to be MIT continue to be MIT.
The big benefit of the relicensing is that closed source code may now
link against libsystemd-login.so and friends.
This logic can be turned off by defining SD_JOURNAL_SUPPRESS_LOCATION
before including sd-journal.h.
This also saves/restores errno in all logging functions, in order to be
useful as logging calls without side-effects.
This also adds a couple of __unlikely__ around the early checks in the
logging calls, in order to minimize the runtime impact.
