[systemd-devel] python - reading the journal

Steven Hiscocks steven-systemd at hiscocks.me.uk
Wed Feb 6 15:05:32 PST 2013

On 06/02/13 00:55, Zbigniew Jędrzejewski-Szmek wrote:
> 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.
> Zbyszek
Sure thing :)

Just also wanted to give you a heads up that I've also got a pull 
request on fail2ban for having it utilise the journal 

Steven Hiscocks

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