[systemd-devel] python - reading the journal

Zbigniew Jędrzejewski-Szmek zbyszek at in.waw.pl
Tue Feb 5 16:55:43 PST 2013

On Tue, Feb 05, 2013 at 11:45:10PM +0000, Steven Hiscocks wrote:
> On 05/02/13 23:00, Zbigniew Jędrzejewski-Szmek wrote:
> >On Tue, Feb 05, 2013 at 09:22:46PM +0000, Steven Hiscocks wrote:
> >>On 05/02/13 02:49, Zbigniew Jędrzejewski-Szmek wrote:
> >>>Hi,
> >>>
> >>>On Mon, Feb 04, 2013 at 10:42:02PM +0000, Steven Hiscocks wrote:
> >>>>I've made the suggested changes and pushed it to github. Feedback
> >>>>welcomed :)
> >>>Thanks!
> >>>
> >>>Some more thoughts on the API below. Some of those are probably
> >>>stupid, but I want to throw them out in the open, for your feedback.
> >>>
> >>>SD_MESSAGE_* are string constants. Shouldn't they be int constants
> >>>like in C? The conversion both ways is pretty simple, but if the
> >>>constants were used outside of journal matches it would be nicer
> >>>to have them as ints. The downside would be that the user
> >>>would have to printf the int to use it in a match. But... see next
> >>>point.
> >>>
> >>>It would be nice to expose the rest of sd-id128 API:
> >>>sd_id128_to_string(3), sd_id128_randomize(3),
> >>>sd_id128_get_machine(3). They would probably go in a separate module
> >>>(systemd.id128), since they are useful in writing journal entries too.
> >>>
> >>Okay. Sounds like they should be dropped from the current code, as
> >>in the future the SD_MESSAGE_* constants will be accessed via python
> >>module systemd.id128?
> >Yes.
> >
> >I think that once pyjournalctl is part of the systemd tree, the constants
> >should be generated from sd-messages.h by a script. Otherwise, we'll
> >be constantly forgetting to update those.
> >
> >>>>>>journal.seek_monotonic(int(monotonic.total_seconds()*1E6), bootid)
> >>>Python interfaces usually use floating point numbers to mean
> >>>seconds. A double has ~16 significant numbers, so the accuracy should
> >>>be enough, so I believe the detail that this is microseconds should
> >>>be hidden.
> >>>
> >>Makes sense to me. Done.
> >>>It would be better to replace PyRun_String with normal C methods,
> >>>but that can be done later.
> >>>
> >>Yeah... I cheated a bit here ;)
> >>>sd_journal_open_directory is not wrapped, but that can be added
> >>>later.
> >>>
> >>Good point, easy enough to add. Done.
> >>>What about renaming Journalctl to Journal? It doesn't really control
> >>>anything :)
> >>>
> >>Yeah. I wasn't too sure on the name when I got started. I was
> >>concious of not clashing with the present systemd.journal. What is
> >>the overall planned structure for the python modules, and where
> >>would this fit in?
> >Good question. Once the SD_MESSAGE constants are moved, pyjournalctl
> >will only export Journalctl and a few constants. If think that could
> >go straight into the systemd.journal module. _journal.so already
> >links against libsystemd-journal.so.0, so I don't think that the
> >additional code for Journalctl will make any different.
> >
> >Specifically: rename pyjournalctl.c to src/python-systemd/_reader.c
> >(unless somebody comes up with a better name), and Journalctl to Journal.
> >In journal.py import Journal and the constants from _reader.
> >
> >>>SD_JOURNAL_LOCAL_ONLY should probably be renamed to LOCAL_ONLY
> >>>(SD_JOURNAL_RUNTIME_ONLY, SYSTEM_ONLY likewise). Here namespaceing
> >>>will be provided by the module, so there's no need for the long name.
> >>>
> >>Good point. Done.
> >>
> >>>Second argument to .seek(), a documentation only change: it would be
> >>>nice to use io.SEEK_SET, io.SEEK_CUR, io.SEEK_END in the description.
> >>>
> >>I had this in mind when developing, but was just a bit lazy and
> >>stuck the number in :-p . Done.
> >>>Should .query_unique() return a set instead? This would make checking
> >>>if an field is present faster, and also underline the fact that those
> >>>are non-repeating entries.
> >>>
> >>Of course! Done.
> >>>Your module will be great for creating a test suite for journal. At the
> >>>same time it will also serve as a test suite for the module.
> >>>
> >>>Zbyszek
> >>>
> >>
> >>Thanks again for the feedback. Latest changes pushed to github.
> >Thank you for your work.
> >
> >Let me know what you think about the proposed integration scheme.
> >
> >Zbyszek
> >
> Okay. Sounds good.
> You'll have to pardon my ignorance :), but my experience of git is
> limited to use of github...
> What's the best way to go about achieving this? Should I fork the
> systemd-repo from freedesktop, putting pyjournalctl.c in as
> src/python-systemd/_reader.c (and make other changes mentioned) and
> use `git format-patch` to submit via email?
I'll do it. I need to throughly check if everything compiles anyway.


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