Merge pull request #41105 from Random-Liu/fix-kuberuntime-log

Automatic merge from submit-queue (batch tested with PRs 38796, 40823, 40756, 41083, 41105)

Let ReadLogs return when there is a read error.

Fixes a bug in kuberuntime log.

Today, @yujuhong found that once we cancel `kubectl logs -f` with `Ctrl+C`, kuberuntime will keep complaining:
```
27939 kuberuntime_logs.go:192] Failed with err write tcp 10.240.0.4:10250->10.240.0.2:53913: write: broken pipe when writing log for log file "/var/log/pods/5bb76510-ed71-11e6-ad02-42010af00002/busybox_0.log": &{timestamp:{sec:63622095387 nsec:625309193 loc:0x484c440} stream:stdout log:[84 117 101 32 70 101 98 32 32 55 32 50 48 58 49 54 58 50 55 32 85 84 67 32 50 48 49 55 10]}
```

This is because kuberuntime keeps writing to the connection even though it is already closed. Actually, kuberuntime should return and report error whenever there is a writing error.

Ref the [docker code](3a4ae1f661/pkg/stdcopy/stdcopy.go (L159-L167))

I'm still creating the cluster and verifying this fix. Will post the result here after that.

/cc @yujuhong @kubernetes/sig-node-bugs

pkg/kubelet/kuberuntime/kuberuntime_logs.go

@@ -191,6 +191,7 @@ func ReadLogs(path string, apiOpts *v1.PodLogOptions, stdout, stderr io.Writer)
 				return nil
 			}
 			glog.Errorf("Failed with err %v when writing log for log file %q: %+v", err, path, msg)
+			return err
 		}
 	}
 }
@@ -299,6 +300,9 @@ type logWriter struct {
 // errMaximumWrite is returned when all bytes have been written.
 var errMaximumWrite = errors.New("maximum write")
 
+// errShortWrite is returned when the message is not fully written.
+var errShortWrite = errors.New("short write")
+
 func newLogWriter(stdout io.Writer, stderr io.Writer, opts *logOptions) *logWriter {
 	w := &logWriter{
 		stdout: stdout,
@@ -342,6 +346,10 @@ func (w *logWriter) write(msg *logMessage) error {
 	if err != nil {
 		return err
 	}
+	// If the line has not been fully written, return errShortWrite
+	if n < len(line) {
+		return errShortWrite
+	}
 	// If there are no more bytes left, return errMaximumWrite
 	if w.remain <= 0 {
 		return errMaximumWrite