Add structcheck, unused, and varcheck linters.

Warn on unused and dead code

Signed-off-by: Daniel Nephin <dnephin@gmail.com>

cmd/containerd/main.go

@@ -8,7 +8,6 @@ import (
 	"net"
 	"os"
 	"os/signal"
-	"runtime"
 	"time"
 
 	"google.golang.org/grpc/grpclog"
@@ -196,18 +195,3 @@ func setLevel(context *cli.Context, config *server.Config) error {
 	}
 	return nil
 }
-
-func dumpStacks() {
-	var (
-		buf       []byte
-		stackSize int
-	)
-	bufferLen := 16384
-	for stackSize == len(buf) {
-		buf = make([]byte, bufferLen)
-		stackSize = runtime.Stack(buf, true)
-		bufferLen *= 2
-	}
-	buf = buf[:stackSize]
-	logrus.Infof("=== BEGIN goroutine stack dump ===\n%s\n=== END goroutine stack dump ===", buf)
-}

cmd/containerd/main_unix.go

@@ -5,7 +5,9 @@ package main
 import (
 	"context"
 	"os"
+	"runtime"
 
+	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
 
 	"github.com/containerd/containerd/log"
@@ -55,3 +57,18 @@ func handleSignals(ctx context.Context, signals chan os.Signal, serverC chan *se
 	}()
 	return done
 }
+
+func dumpStacks() {
+	var (
+		buf       []byte
+		stackSize int
+	)
+	bufferLen := 16384
+	for stackSize == len(buf) {
+		buf = make([]byte, bufferLen)
+		stackSize = runtime.Stack(buf, true)
+		bufferLen *= 2
+	}
+	buf = buf[:stackSize]
+	logrus.Infof("=== BEGIN goroutine stack dump ===\n%s\n=== END goroutine stack dump ===", buf)
+}