logging: Allow SetLogger to be called multiple times

Now that the `SetLogger()` functions accept a `logrus.Entry`, they can
access the fields that have already been set for the logger and
re-apply them if `SetLogger()` is called multiple times.

This fixes a bug whereby the logger functions -- which are necessarily
called multiple times [1] -- previously ended up applying any new fields
the specified logger contained, but erroneously removing any additional
fields added since `SetLogger()` was last called.

Partially fixes #519.

--
[1] - https://github.com/kata-containers/runtime/pull/468

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

virtcontainers/api.go

@@ -19,11 +19,12 @@ func init() {
 	runtime.LockOSThread()
 }
 
-var virtLog *logrus.Entry
+var virtLog = logrus.WithField("source", "virtcontainers")
 
 // SetLogger sets the logger for virtcontainers package.
 func SetLogger(logger *logrus.Entry) {
-	virtLog = logger.WithField("source", "virtcontainers")
+	fields := virtLog.Data
+	virtLog = logger.WithFields(fields)
 
 	deviceApi.SetLogger(virtLog)
 }

virtcontainers/device/api/interface.go

@@ -12,16 +12,17 @@ import (
 	"github.com/kata-containers/runtime/virtcontainers/device/config"
 )
 
-var devLogger *logrus.Entry
+var devLogger = logrus.WithField("subsystem", "device")
 
 // SetLogger sets the logger for device api package.
 func SetLogger(logger *logrus.Entry) {
-	devLogger = logger
+	fields := devLogger.Data
+	devLogger = logger.WithFields(fields)
 }
 
 // DeviceLogger returns logger for device management
 func DeviceLogger() *logrus.Entry {
-	return devLogger.WithField("subsystem", "device")
+	return devLogger
 }
 
 // DeviceReceiver is an interface used for accepting devices

virtcontainers/pkg/oci/utils.go

@@ -128,14 +128,15 @@ func (config *RuntimeConfig) AddKernelParam(p vc.Param) error {
 	return config.HypervisorConfig.AddKernelParam(p)
 }
 
-var ociLog = logrus.FieldLogger(logrus.New())
+var ociLog = logrus.WithFields(logrus.Fields{
+	"source":    "virtcontainers",
+	"subsystem": "oci",
+})
 
 // SetLogger sets the logger for oci package.
 func SetLogger(logger *logrus.Entry) {
-	ociLog = logger.WithFields(logrus.Fields{
-		"source":    "virtcontainers",
-		"subsystem": "oci",
-	})
+	fields := ociLog.Data
+	ociLog = logger.WithFields(fields)
 }
 
 func cmdEnvs(spec CompatOCISpec, envs []vc.EnvVar) []vc.EnvVar {