[rsyslog] backward compatibility...

Raoul Bhatia [IPAX] r.bhatia at ipax.at
Mon Dec 17 11:17:03 CET 2007


Rainer Gerhards wrote:
> Hi all,
> 
> I would appreciate your feedback on backward compatibility. I have
> started to create a loadable input module interface in rsyslog v3. My
> first input module is the mark message handler (because it has almost no
> code, so it was a good example of what needs to be done...). I have now
> basically have finished an initial version. The interface needs to be
> changed in the longer term, but I'll postpone that until I've done a bit
> more work on the config interface. Now I am facing a problem with
> backward compatibility:
> 
> In sysklogd/rsyslog pre-v3, the -m option controls how often mark
> messages are written (with -m0 disabling this mechanism). In v3, the
> $MarkMessagePeriod config file directive does the same. However, a
> $modload immark is necessary to activate that functionality because
> otherwise the module is not loaded (which is good if it is not needed).
> When trying to remain backward-compatible, I have an issue when the -m
> option is absent. If so, that means a mark message period of 20 minutes.
> However, it is hard to detect what may be intended in v3 if this option
> is not present. Does it mean the former default (running as a drop-in
> replacement) or does it actually mean that no mark messages should
> appear if no such directive is in rsyslog.conf?
> 
> Do you think it would be acceptable to not emit messages in this case,
> slightly breaking backward compatibility? Or should I come up with a
> solution. The later would probably require a specific option setting to
> disable the -m option and its default (somehow telling "I am not running
> in v2 compatibility mode").
> 
> I am not sure what is best...

i would use the opportunity and not hesitate to use a
make-everything-right-even-if-we-break-something approach.

upgrading seems to not be trivial, as one needs to go through the config
files anyway. so lets do things right and maybe issue some error/warning
message on obsolete options (like -m).

cheers,
raoul
ps: i hope i'm getting you right ;)
-- 
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DI (FH) Raoul Bhatia M.Sc.          email.          r.bhatia at ipax.at
Technischer Leiter

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