[systemd-devel] [PATCH 4/4] Add a new tmpfiles.d snippets to set the NOCOW the journal.

[Goffredo Baroncelli]

On 2015-04-12 15:12, Lennart Poettering wrote:
> On Sat, 11.04.15 17:07, Zbigniew Jędrzejewski-Szmek (zbyszek at in.waw.pl) wrote:
> 
>>>> That's the problem: current functionality works no matter where you
>>>> store the files, but it's hard to provide the same level of
>>>> flexibility with the tmpfiles-based solution.
>>>
>>> Well, but we never store files outside of /var/log/journal,
>>> /var/log/journal/%m and /var/log/journal/remote/, do we? 
>> We can, if instructed to do so. journal-remote can store files wherever.
>>
>> Original motivation for this patch was to make the NOCOW on journal files
>> configurable without too much fuss and without making it an explicit option.
>> Journal files on btrfs without NOCOW are rather slow, so it seems that most
>> people will want NOCOW on. But with the proposed patch, people would want
>> to add the tmpfile snippet to set NOCOW for every location they write too,
>> which is very visible and requires explicit configuration. Doing this in
>> journal-file directly was simple, synchronous, and worked everywhere, and
>> we are replacing this with a more complicated and more brittle scheme.
>>
>> Dunno, if you think things are better this way, I'm fine with that,
>> since both schemes should get the job done. But in the end, adding a
>> switch in journald.conf seems more in the systemd spirit of doing the right
>> thing automatically and also less work for both sides...
> 
> What about this solution: let's go the tmpfiles way, but also add some
> code to the journal file writer to log at INFO level an actionable
> recommendation to turn on the c flag on the directory if we notice
> that the newly created file doesn't have it, and it is located on
> btrfs?

After the work that I done to the tmpfiles, I have to agree with Zbyszek. Adding an option to the journal.conf file is the more reasonable thing to do.

If we add code that performs only a check in the code of journal, I think that we have the worst solution:
- journal code is still aware of the NOCOW attribute (== more code complexity)
- the user had to update/manage a tmpfile.d  manually

Let me to suggest the opposite solution:
- add a switch in the journald.conf file
- add a check that raise a warning if the NOCOW flag is not-used/used

GB



> 
> That way, folks who use the tools on non-default directories will at
> least be guided to an explanation of the general problem.
> 
> Lennart
> 


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