Samba debug

Martin Schwenke martin at
Mon Dec 5 20:14:21 UTC 2016

On Mon, 28 Nov 2016 10:47:27 +0100, Andreas Schneider <asn at>

> On Monday, 28 November 2016 15:08:50 CET Martin Schwenke wrote:
> > Amitay and I are in the process of moving to (more directly) use
> > Samba's debug support.  At the moment we are doing file and syslog
> > logging using CTDB's own backends, which are hooked into debug.[ch]
> > using the DEBUG_CALLBACK support.  
> Hey Martin,
> thanks for looking into this mess!
> > We have come across (at least!) a couple of idiosyncrasies in
> > debug.[ch]...  :-)
> > 
> > * Headers and messages can be interleaved in file logging
> > 
> >   Header and message are written using 2 separate write() calls (via
> >   dbghdrclass(), dbgtext()). So, if 2 processes are writing to the same
> >   log file, then you can get <header1>, <header2>, <message1>,
> >   <message2>... or other variations.
> > 
> >   This could be improved if the above 2 functions added to the buffer
> >   and a single write() was then used.
> > 
> > * When logging to syslog, header information is duplicated
> > 
> >   That is the date and time (and maybe PID, progname), are present in
> >   the output of dbghdrclass() and syslog adds them as well.
> > 
> >   All the backends other than file (syslog, systemd, lttng,
> >   GPFS) probably add their own timestamps.
> > 
> >   This could be improved by having dbghdrclass() omit these items and
> >   have the file backend add those that are configured.
> > 
> > For CTDB logging we only really want single-line messages, with an
> > appropriate non-redundant header.  For file we want a header
> > (date, time, progname, pid).  For syslog we want to send just a bare
> > message and have syslog do the rest.
> > 
> > Suggestions?  Ideas?  :-)  
> Please take a look into the options:
> 	debug prefix timestamp
> 	timestamp logs
> They are related and are totally broken.

Well, I don't think they're totally broken.  If you read the
documentation very carefully then "debug prefix timestamp" does what it

However, there should really be 3 options:

  debug location        = Add the file location
  debug function        = Add the function name
  debug header prefix   = Don't add a newline after header

This is all somewhat broken for non-file output, since the header and
text are logged via separate calls to the backend.  I have a branch
that could fix this, since I've pushed logging of the header into the
backend.  However, at the moment I still use a separate call for
the header.  This essentially makes DEBUG_ADD() useless, since it
prints the last header that was produced - however, at least no time is
taken to generate the extra header right now.

> The suggestion I have is that we need tests for the debug system. We have 
> features which do not work and nobody notices.
> Testing debug is possible using the Mock object [1][2] support in cmocka [3].

I agree and will look into it.  However, I don't have an endless bucket
of time for this.  One problem is that I doubt testing would have
caught either of the issues I listed above!  ;-)

peace & happiness,

More information about the samba-technical mailing list