* Add basic logging functionality:

 - Introduce a customer global logger such that all log.* messages are logged to syslog. - Modified all calls to panic() to first write to the logger. - Changed error handling for critical system commands to ensure the errors are logged first. 

1 files changed, 74 insertions, 0 deletions

diff --git a/logger/logger.go b/logger/logger.go
new file mode 100644
index 0000000000..6a7b15f4ae
--- /dev/null
+++ b/logger/logger.go
@@ -0,0 +1,74 @@
+package logger
+
+import (
+	"fmt"
+	"log"
+	"log/syslog"
+	"os"
+	"runtime/debug"
+	"strings"
+)
+
+// Name appearing in syslog / journald entries.
+const syslogName = "SnappyLogger"
+
+// SnappyLogger logging object
+type SnappyLogger struct {
+	systemLog *syslog.Writer
+	disabled bool
+}
+
+// Write implements the io.Writer interface
+func (l *SnappyLogger) Write(bytes []byte) (int, error) {
+	str := string(bytes)
+	length := len(str)
+
+	// Now, log to the systemlog.
+	if err := l.systemLog.Info(str); err != nil {
+	return 0, err
+	}
+
+	return length, nil
+}
+
+// New create a new SnappyLogger
+func New() *SnappyLogger {
+	var err error
+
+	l := new(SnappyLogger)
+
+	l.systemLog, err = syslog.New(syslog.LOG_NOTICE|syslog.LOG_LOCAL0, syslogName)
+
+	// By default, fail hard if any aspect of the logger fails.
+	// However, this behaviour can be overriden since if logging
+	// fails, it would otherwise not be possible to upgrade a system
+	// (for example to fix a logger bug).
+	l.disabled = os.Getenv("SNAPPY_LOGGING_DISABLE") != ""
+
+	if err != nil && !l.disabled {
+	panic(fmt.Sprintf("error connecting to system logger: %v", err))
+	}
+
+	return l
+}
+
+// LogError log the specified error (if set), then return it to be dealt with by
+// higher-level parts of the system.
+func LogError(err error) error {
+
+	if err == nil {
+	return nil
+	}
+
+	stack := debug.Stack()
+
+	log.Printf("A snappy error occurred: %v\n", err)
+
+	log.Printf("Stack trace:\n")
+
+	for _, line := range strings.Split(string(stack), "\n") {
+	log.Printf("%s\n", line)
+	}
+
+	return err
+}