[libvirt] [PATCH] logging: remove concept of default log priority

[Erik Skultety]

On 16/06/16 15:37, Daniel P. Berrange wrote:
> On Tue, May 31, 2016 at 10:52:35AM +0200, Erik Skultety wrote:
>> On 11/05/16 16:12, Daniel P. Berrange wrote:
>>> The logging framework has categories which can be selectively
>>> enabled/disabled by setting a suitable LIBVIRT_LOG_FILTERS
>>> environment variable or config file setting.
>>>
>>> Along side that we also have the LIBVIRT_DEBUG environment
>>> variable which unconditionally enables every single category
>>> at DEBUG level. With the amount of logging produced by libvirt
>>> these days, the signal/noise ratio in the output from setting
>>> LIBVIRT_DEBUG is to poor for it to be useful.
>>>
>>> Originally the LIBVIRT_DEBUG env variable had a very specific
>>> use case - it resulted in logging of anything in our public
>>> API entrypoints. eg it turned on src/libvirt.c debugging and
>>> nothing else. Additionally it would always result in log
>>> messages being sent to stderr.
>>>
>>> When applied to any of the daemons, the log output no longers
>>> gets sent to stderr, but rather to whatever default log output
>>> has been configured by the daemon. If no log_outputs setting
>>> or LIBVIRT_LOG_OUTPUTS env is set, then messages will often
>>> go to the systemd journal or a /var/log/libvirt/libvirtd.log
>>> file rather than stderr.
>>>
>>> These factors have conspired to make the LIBVIRT_DEBUG env
>>> and/or default log priority to be pretty useless in the real
>>> world.
>>>
>>> This change attempts to take us back towards the original
>>> semantics of the LIBVIRT_DEBUG env variable as follows.
>>>
>>> If LIBVIRT_DEBUG is set to a plain integer, or log level
>>> string, then it will turn on logging for the "libvirt" log
>>> category at that level. Any other string will be parsed in
>>> the same way as LIBVIRT_LOG_FILTERS would be. In all cases
>>> use of LIBVIRT_DEBUG will result in an explicit output being
>>> added for stderr. This ensures that messages always go to
>>> stderr, even if other outputs are already configured.
>>>
>>> IOW,   LIBVIRT_DEBUG=1 virsh or LIBVIRT_DEBUG=1 libvirtd
>>> will both result in printing logs of libvirt public API
>>> calls to stderr. Meanwhile setting LIBVIRT_DEBUG="1:qemu"
>>> is equivalent to setting LIBVIRT_LOG_FILTERS="1:qemu" and
>>> LIBVIRT_LOG_OUTPUTS="1:stderr"
>>>
>>> Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
> 
> FYI, I'm still thinking about how to proceed with this patch
> given the feedback so far....so consider this "on hold" until
> I come up with a better idea.
> 
> In the meantime we must not make the problem worse. ie we should
> *not* expose the default logging level config via the admin API.
> Only expose log filters + outputs.
> 
> Regards,
> Daniel
> 
Sure, that works for me just fine.

Erik