Online backup API for systemd-journal?

[Etienne Doms <etienne.doms@xxxxxxxxx>]

Hi,

I have some embedded systems in the wild, not connected to anything,
on which you can push a button "something went wrong, create a dump".
Then later I can fetch the said dump and inspect it.

I'd like to include the whole journal, for the current boot, in a
binary format so that I can later do "journalctl --file
path/to/journal-dump.bin" from another machine. I understand that
internally everything is stored in /var/log/journal/<machine-id>, but
I guess that I cannot blindly tar/cp the .journal files, since this
would be racy.

So, is there an API to safely dump a big ".journal" file containing a
snapshot of "journalctl -b"? I could not find anything in the
documentation, sorry in advance if I missed something obvious.

For now I just dump it with "-o json" which is fine, but then I cannot
feed another journalctl with the given json, and need to do manual
filtering.

Thanks,
Etienne