How to debug SASL2 and its plugin?

[Xu, Qiang (FXSGSC)]

> -----Original Message-----
> From: Alexey Melnikov [mailto:alexey.melnikov at isode.com] 
> Sent: Thursday, August 06, 2009 4:18 AM
> To: Xu, Qiang (FXSGSC)
> Cc: cyrus-sasl at lists.andrew.cmu.edu
> Subject: Re: How to debug SASL2 and its plugin?
> 
> Try setting the "log_level" option to one of these numbers in 
> the application config file.

How to use "log_level" option? Is it used in command-line, or in the code? 

Could you give me some example on using this?

Thanks,
Xu Qiang