Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Wed, 18 Apr 2012 16:04:34 +0200

On Wednesday, April 18, 2012, [email protected] wrote:
> > One simple idea would be to add a bit to the asynTrace flags,
> > ASYN_TRACE_NOREPEATS.  The asynTrace facility could remember the
> > previous error message for a particular pasynUser, and if the next one
> > is the same (except for the time stamp) then the message would not be
> > output.
> 
> The drivers would then need to decide when to reset that flag, to print
> the message again. For example, if a comms error was resolved, but
> re-occurred again (say, an hour later). You would want a new message in
> that case.
> 
> Seems like, in general, people wouldn't mind this functionality in the
> errlog layer. Perhaps as Nick suggested as a library that implemented
> the same interface, and was plugged in somehow. Or, could modify errlog
> by adding a function call in each function, that checks the message and
> rejects or accepts it.

Errlog is /not/ the right place to ensure error messages are issued in a 
sensible way. Generic filtering of messages is too weak, it cannot know 
which messages are important and which are not. It cannot decide which 
errors are merely consequences of something at a lower level going wrong. It 
is also very inefficient to filter messages that should not be issued in the 
first place.

It is the driver that knows whether a port is disconnected. It can and 
should report this exactly once. It can and should report, again only once, 
when the port is connected again. Device support should /not/ issue an error 
message if a lower level (i.e. driver) indicates that it already did so.

Note I am not talking about special debugging support. This is for normal 
operation, where you do /not/ want log files to increase to Gigabytes in a 
few days, simply because someone pulled a plug or forgot to switch on some 
seldom looked at device after maintenance.

Cheers
Ben

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System