[systemd-devel] python - reading the journal

David Strauss david at davidstrauss.net
Thu Feb 7 15:19:03 PST 2013

Can we spend some time on IRC prepping the systemd patch? I'd like to
get that rolling.

On Wed, Feb 6, 2013 at 3:05 PM, Steven Hiscocks
<steven-systemd at hiscocks.me.uk> wrote:
> 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
> (https://github.com/fail2ban/fail2ban/pull/82)
> --
> Steven Hiscocks
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David Strauss
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