[doc][log] Add suervey for seelog #26

- detail xml config, filter by level, file, function (require calling runtime,
expensive)
- many small files, some just have one interface (quite java style ...)
- created back in 2011 ...

log2/doc/seelog.md

@@ -2,4 +2,56 @@
 
 https://github.com/cihub/seelog
 
-has a java style xml config ...
+it has very detailed config (like log4j), also allow control logging behaviour of library.
+besides level, it also support file and function pattern.
+
+````xml
+<seelog minlevel="info">
+	<exceptions>
+		<exception filepattern="test*" minlevel="error"/>
+        <exception funcpattern="*test*" filepattern="tests.go" levels="off"/>
+        <exception funcpattern="*perfCritical" minlevel="critical"/>
+	</exceptions>
+</seelog>
+````
+
+- patterns are matched using string comparison (not using regexp, custom recursive implementation)
+
+````go
+// logConfig stores logging configuration. Contains messages dispatcher, allowed log level rules
+// (general constraints and exceptions)
+type logConfig struct {
+	Constraints    logLevelConstraints  // General log level rules (>min and <max, or set of allowed levels)
+	Exceptions     []*LogLevelException // Exceptions to general rules for specific files or funcs
+	RootDispatcher dispatcherInterface  // Root of output tree
+}
+
+// LogLevelException represents an exceptional case used when you need some specific files or funcs to
+// override general constraints and to use their own.
+type LogLevelException struct {
+	funcPatternParts []string
+	filePatternParts []string
+
+	funcPattern string
+	filePattern string
+
+	constraints logLevelConstraints
+}
+
+// stringMatchesPattern check whether testString matches pattern with asterisks.
+// Standard regexp functionality is not used here because of performance issues.
+func stringMatchesPattern(patternparts []string, testString string) bool {
+	// ...
+}
+````
+
+````go
+// innerLoggerInterface is an internal logging interface
+type innerLoggerInterface interface {
+	innerLog(level LogLevel, context LogContextInterface, message fmt.Stringer)
+	Flush()
+}
+
+````
+
+- log -> dispatcher -> write to output