RFE: libguestfs logging should be connected up to openstack logging

[Richard Jones]

https://bugzilla.redhat.com/show_bug.cgi?id=1064948

We were trying to chase up a bug in libguestfs integration with
OpenStack. It was made much harder because the only way to diagnose
the bug was to manually run the nova service after manually setting
environment variables:
http://libguestfs.org/guestfs-faq.1.html#debugging-libguestfs

It would be much nicer if:

(1) There was a Nova setting to enable debugging, like:
      libguestfs_debug = 1
or something along those lines.

(2) Nova used the events API to collect libguestfs debug messages
and push them into Openstack's own logging system. See code
example below.

---------

Here is how you enable logging programmatically and capture
the log messages.

(a) As soon as possible after creating the guestfs handle, call
either (or better, both) of these functions:

g.set_trace (1) # just traces libguestfs API calls
g.set_verbose (1) # verbose debugging

(b) Register an event handler like this:

events = guestfs.EVENT_APPLIANCE | guestfs.EVENT_LIBRARY \
         | guestfs.EVENT_WARNING | guestfs.EVENT_TRACE
g.set_event_callback (log_callback, events)

(c) The log_callback function should look something like this:

def log_callback (ev,eh,buf,array):
    if ev == guestfs.EVENT_APPLIANCE:
        buf = buf.rstrip()
    # What just happened?
    LOG.debug ("event=%s eh=%d buf='%s' array=%s" %
               (guestfs.event_to_string (ev), eh, buf, array))

There is a fully working example here:

https://github.com/libguestfs/libguestfs/blob/master/python/t/420-log-messages.py

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/124700

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/124700
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=a2f843e0c6cd315f7e130661cc1d0b4b959cbc54
Submitter: Jenkins
Branch: master

commit a2f843e0c6cd315f7e130661cc1d0b4b959cbc54
Author: Sahid Orentino Ferdjaoui <email address hidden>
Date: Mon Sep 29 05:49:15 2014 -0400

    vfs: guestfs logging integration

    Adds support to enable guestfs logging.

    Change-Id: I46c5ec6606e4a2eb8277b081d0c773ceb6d36c4c
    DocImpact: New group of option has been introduced "guestfs"
    Closes-Bug: #1279857