Add README.md for kernel monitor

Author: Random-Liu

pkg/kernelmonitor/README.md

@@ -0,0 +1,56 @@
+# Kernel Monitor
+
+*Kernel Monitor* is a problem daemon in node problem detector. It monitors kernel log
+and detects known kernel issues following predefined rules.
+
+The Kernel Monitor matches kernel issues according to a set of predefined rule list in
+[`config/kernel-monitor.json`](https://github.com/kubernetes/node-problem-detector/blob/master/config/kernel-monitor.json).
+The rule list is extensible.
+
+## Limitations
+
+* Kernel Monitor only supports file based kernel log now. It doesn't support log tools
+like journald. There is an [open issue](https://github.com/kubernetes/node-problem-detector/issues/14)
+to add journald support.
+
+* Kernel Monitor has assumption on kernel log format, now it only works on Ubuntu and
+Debian. However, it is easy to extend it to [support other log format](#support-other-log-format).
+
+## Add New NodeConditions
+
+To support new node conditions, you can extend the `conditions` field in
+`config/kernel-monitor.json` with new condition definition:
+
+```json
+{
+  "type": "NodeConditionType",
+  "reason": "CamelCaseDefaultNodeConditionReason",
+  "message": "arbitrary default node condition message"
+}
+```
+
+## Detect New Problems
+
+To detect new problems, you can extend the `rules` field in `config/kernel-monitor.json`
+with new rule definition:
+
+```json
+{
+  "type": "temporary/permanent",
+  "condition": "NodeConditionOfPermanentIssue",
+  "reason": "CamelCaseShortReason",
+  "message": "regexp matching the issue in the kernel log"
+}
+```
+
+## Change Log Path
+
+Kernel log in different OS distros may locate in different path. The `log`
+field in `config/kernel-monitor.json` is the log path inside the container.
+You can always configure it to match your OS distro.
+
+## Support Other Log Format
+
+Kernel monitor uses [`Translator`](https://github.com/kubernetes/node-problem-detector/blob/master/pkg/kernelmonitor/translator/translator.go)
+plugin to translate kernel log the internal data structure. It is easy to
+implement a new translator for a new log format.