router: cleanup naming, error reporting and logging.

Per reviewer's suggestion:
* Rename Newxyz to Init(), since not returning anything.
* Moved logging to caller side.
* Normalized errors a bit.

pkg/private/processmetrics/BUILD.bazel

@@ -10,50 +10,50 @@ go_library(
     visibility = ["//visibility:public"],
     deps = select({
         "@io_bazel_rules_go//go/platform:aix": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:android": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
             "@com_github_prometheus_client_golang//prometheus:go_default_library",
             "@com_github_prometheus_procfs//:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:darwin": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:dragonfly": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:freebsd": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:illumos": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:ios": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:js": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:linux": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
             "@com_github_prometheus_client_golang//prometheus:go_default_library",
             "@com_github_prometheus_procfs//:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:netbsd": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:openbsd": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:plan9": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:solaris": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "@io_bazel_rules_go//go/platform:windows": [
-            "//pkg/log:go_default_library",
+            "//pkg/private/serrors:go_default_library",
         ],
         "//conditions:default": [],
     }),

pkg/private/processmetrics/processmetrics_linux.go

@@ -32,7 +32,7 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/procfs"
 
-	"github.com/scionproto/scion/pkg/log"
+	"github.com/scionproto/scion/pkg/private/serrors"
 )
 
 var (
@@ -157,19 +157,18 @@ func (c *procStatCollector) Collect(ch chan<- prometheus.Metric) {
 	)
 }
 
-// NewProcStatCollector creates a new collector for process statistics.
+// Init creates a new collector for process statistics.
 // The collector exposes those statistics to prometheus and responds
 // to scraping requests. Call this only once per process or get an error.
 // It is safe to ignore errors from this but prometheus may lack some
 // metrics.
-func NewProcStatCollector() error {
+func Init() error {
 	me := os.Getpid()
 	taskPath := filepath.Join(procfs.DefaultMountPoint, strconv.Itoa(me), "task")
 	taskDir, err := os.Open(taskPath)
 	if err != nil {
-		log.Error("NewProcStatCollector: opening /proc/pid/task/ failed",
-			"pid", me, "error", err)
-		return err
+		return serrors.WrapStr("Opening /proc/pid/task/ failed", err,
+			"pid", me)
 	}
 
 	c := &procStatCollector{
@@ -179,18 +178,15 @@ func NewProcStatCollector() error {
 
 	err = c.updateStat()
 	if err != nil {
-		log.Error("NewProcStatCollector: first update failed", "error", err)
 		// Ditch the broken collector. It won't do anything useful.
-		return err
+		return serrors.WrapStr("First update failed", err)
 	}
 
 	// It works. Register it so prometheus milks it.
 	err = prometheus.Register(c)
 	if err != nil {
-		log.Error("NewProcStatCollector", "registration failed", err)
-		return err
+		return serrors.WrapStr("Registration failed", err)
 	}
 
-	log.Info("NewProcStatCollector", "collector", c)
 	return nil
 }

pkg/private/processmetrics/processmetrics_other.go

@@ -21,10 +21,9 @@
 package processmetrics
 
 import (
-	"github.com/scionproto/scion/pkg/log"
+	"github.com/scionproto/scion/pkg/private/serrors"
 )
 
-func NewProcStatCollector() error {
-	log.Info("NewProcStatCollector not supported for this platform")
-	return error("Not supported for this platform)
+func Init() error {
+	return serrors.New("Not supported for this platform")
 }

router/dataplane.go

@@ -2521,7 +2521,12 @@ func (d *DataPlane) initMetrics() {
 
 	// Start our custom /proc/pid/stat collector to export iowait time and
 	// (in the future) other process-wide metrics that prometheus does not.
-	_ = processmetrics.NewProcStatCollector()
+	err := processmetrics.Init()
+
+	// we can live without these metrics. Just log the error.
+	if err != nil {
+		log.Error("Could not initialize processmetrics", "err", err)
+	}
 }
 
 func initInterfaceMetrics(metrics *Metrics, labels prometheus.Labels) interfaceMetrics {