[PATCH 5/8] kbase: debuglogs: Add a section describing log outputs and filters

[Peter Krempa]

Outline what the given settings influence.

Signed-off-by: Peter Krempa <pkrempa at redhat.com>
---
 docs/kbase/debuglogs.rst | 67 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)

diff --git a/docs/kbase/debuglogs.rst b/docs/kbase/debuglogs.rst
index cba57e020d..9ba39b9f85 100644
--- a/docs/kbase/debuglogs.rst
+++ b/docs/kbase/debuglogs.rst
@@ -17,6 +17,73 @@ Moreover, libvirt catches stderr of all running domains. These can be useful as
 well.


+Logging settings in libvirt
+===========================
+
+Log levels
+----------
+
+Libvirt produces log entries in 4 priority levels; higher priority level meaning
+more severe log entries, which in turn means less of them. The log level are
+used by `Log outputs`_ and `Log filters`_ below):
+
+  * ``1: DEBUG``
+  * ``2: INFO``
+  * ``3: WARNING``
+  * ``4: ERROR``
+
+For debugging it's necessary to capture ``DEBUG`` level entries as the name
+implies.
+
+Log outputs
+-----------
+
+Log outputs describe where the log messages are being recorded. The outputs
+are described by a space-separated list of tuples in the following format:
+
+::
+
+  level:output
+
+``level`` refers to the minimum priority level of entries recorded in the output.
+
+``output`` is one of the following:
+
+  ``file:FILENAME``
+    Logging messages are appended to FILENAME.
+
+  ``journald``
+    Logging goes to the ``journald`` logging daemon.
+
+  ``stderr``
+    Logging goes to the standard error output stream of the libvirt daemon.
+
+  ``syslog:name``
+    Logging goes to syslogd. ``name`` is used to identify the entries.
+
+The default output on systems running ``journald`` is ``3:journald``. Note that
+``journald`` can trottle the amount of logs per process so for capturing debug
+logs of libvirt daemons a file output should be used in addition to the output
+to the logging daemon e.g.:
+
+::
+
+  "1:file:/var/log/libvirt/libvirtd.log 3:journald"
+
+
+Log filters
+-----------
+
+Log filters allow to avoid logging of messages which are not relevant to the
+cause. The log filters is a space-separated list of tuples in the format
+``level:identifer`` and limits messages which match ``identifier`` to the
+configured log level. Identifier supports globbing patterns such as ``*``.
+
+As ``identifier`` is based on internal naming of modules, the best approach is
+to select one of `Example filter settings`_. It's also always better to have
+more information than lack something important.
+
+
 How to turn on debug logs for libvirt
 =====================================

-- 
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