Send error message to docker/kubectl exec on failure

Containerd uses the last error message sent to the log to
print as failure cause for create/exec. This required a
few changes in the logging logic for runsc:
  - cmd.Errorf/Fatalf: now writes a message with 'error'
    level to containerd log, in addition to stderr and
    debug logs, like before.
  - log.Infof/Warningf/Fatalf: are not sent to containerd
    log anymore. They are mostly used for debugging and not
    useful to containerd. In most cases, --debug-log is
    enabled and this avoids the logs messages from being
    duplicated.
  - stderr is not used as default log destination anymore.
    Some commands assume stdio is for the container/process
    running inside the sandbox and it's better to never use
    it for logging. By default, logs are supressed now.

PiperOrigin-RevId: 251881815

1 files changed, 72 insertions, 0 deletions

diff --git a/runsc/cmd/error.go b/runsc/cmd/error.go
new file mode 100644
index 000000000..700b19f14
--- /dev/null
+++ b/runsc/cmd/error.go
@@ -0,0 +1,72 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cmd
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"time"
+
+	"github.com/google/subcommands"
+	"gvisor.googlesource.com/gvisor/pkg/log"
+)
+
+// ErrorLogger is where error messages should be written to. These messages are
+// consumed by containerd and show up to users of command line tools,
+// like docker/kubectl.
+var ErrorLogger io.Writer
+
+type jsonError struct {
+	Msg   string    `json:"msg"`
+	Level string    `json:"level"`
+	Time  time.Time `json:"time"`
+}
+
+// Errorf logs error to containerd log (--log), to stderr, and debug logs. It
+// returns subcommands.ExitFailure for convenience with subcommand.Execute()
+// methods:
+//    return Errorf("Danger! Danger!")
+//
+func Errorf(format string, args ...interface{}) subcommands.ExitStatus {
+	// If runsc is being invoked by docker or cri-o, then we might not have
+	// access to stderr, so we log a serious-looking warning in addition to
+	// writing to stderr.
+	log.Warningf("FATAL ERROR: "+format, args...)
+	fmt.Fprintf(os.Stderr, format+"\n", args...)
+
+	j := jsonError{
+		Msg:   fmt.Sprintf(format, args...),
+		Level: "error",
+		Time:  time.Now(),
+	}
+	b, err := json.Marshal(j)
+	if err != nil {
+		panic(err)
+	}
+	if ErrorLogger != nil {
+		ErrorLogger.Write(b)
+	}
+
+	return subcommands.ExitFailure
+}
+
+// Fatalf logs the same way as Errorf() does, plus *exits* the process.
+func Fatalf(format string, args ...interface{}) {
+	Errorf(format, args...)
+	// Return an error that is unlikely to be used by the application.
+	os.Exit(128)
+}