oci: allow to specify what runtimes support JSON

add a new configuration `runtime_supports_json` to list what OCI
runtimes support the --log-format=json option.  If the runtime is not
listed here, libpod will redirect stdout/stderr from the runtime
process.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

libpod.conf

@@ -106,6 +106,10 @@ num_locks = 2048
 # Default OCI runtime
 runtime = "runc"
 
+# List of the OCI runtimes that support --format=json.  When json is supported
+# libpod will use it for reporting nicer errors.
+runtime_supports_json = ["runc"]
+
 # Paths to look for a valid OCI runtime (runc, runv, etc)
 [runtimes]
 runc = [

libpod/oci.go

@@ -58,6 +58,7 @@ type OCIRuntime struct {
 	logSizeMax    int64
 	noPivot       bool
 	reservePorts  bool
+	supportsJSON  bool
 }
 
 // syncInfo is used to return data from monitor process to daemon
@@ -75,7 +76,7 @@ type ociError struct {
 }
 
 // Make a new OCI runtime with provided options
-func newOCIRuntime(oruntime OCIRuntimePath, conmonPath string, conmonEnv []string, cgroupManager string, tmpDir string, logSizeMax int64, noPivotRoot bool, reservePorts bool) (*OCIRuntime, error) {
+func newOCIRuntime(oruntime OCIRuntimePath, conmonPath string, conmonEnv []string, cgroupManager string, tmpDir string, logSizeMax int64, noPivotRoot bool, reservePorts bool, supportsJSON bool) (*OCIRuntime, error) {
 	runtime := new(OCIRuntime)
 	runtime.name = oruntime.Name
 	runtime.path = oruntime.Paths[0]
@@ -86,6 +87,7 @@ func newOCIRuntime(oruntime OCIRuntimePath, conmonPath string, conmonEnv []strin
 	runtime.logSizeMax = logSizeMax
 	runtime.noPivot = noPivotRoot
 	runtime.reservePorts = reservePorts
+	runtime.supportsJSON = supportsJSON
 
 	runtime.exitsDir = filepath.Join(runtime.tmpDir, "exits")
 	runtime.socketsDir = filepath.Join(runtime.tmpDir, "socket")

libpod/oci_linux.go

@@ -223,7 +223,7 @@ func (r *OCIRuntime) createOCIContainer(ctr *Container, cgroupParent string, res
 	args = append(args, "-b", ctr.bundlePath())
 	args = append(args, "-p", filepath.Join(ctr.state.RunDir, "pidfile"))
 	args = append(args, "--exit-dir", r.exitsDir)
-	if logLevel != logrus.DebugLevel {
+	if logLevel != logrus.DebugLevel && r.supportsJSON {
 		args = append(args, "--runtime-arg", "--log-format=json", "--runtime-arg", "--log", fmt.Sprintf("--runtime-arg=%s", ociLog))
 	}
 	if ctr.config.ConmonPidFile != "" {
@@ -423,11 +423,13 @@ func (r *OCIRuntime) createOCIContainer(ctr *Container, cgroupParent string, res
 		}
 		logrus.Debugf("Received container pid: %d", ss.si.Pid)
 		if ss.si.Pid == -1 {
-			data, err := ioutil.ReadFile(ociLog)
-			if err == nil {
-				var ociErr ociError
-				if err := json.Unmarshal(data, &ociErr); err == nil {
-					return errors.Wrapf(ErrOCIRuntime, "%s", strings.Trim(ociErr.Msg, "\n"))
+			if r.supportsJSON {
+				data, err := ioutil.ReadFile(ociLog)
+				if err == nil {
+					var ociErr ociError
+					if err := json.Unmarshal(data, &ociErr); err == nil {
+						return errors.Wrapf(ErrOCIRuntime, "%s", strings.Trim(ociErr.Msg, "\n"))
+					}
 				}
 			}
 			// If we failed to parse the JSON errors, then print the output as it is

libpod/runtime.go

@@ -151,6 +151,8 @@ type RuntimeConfig struct {
 	OCIRuntime string `toml:"runtime"`
 	// OCIRuntimes are the set of configured OCI runtimes (default is runc)
 	OCIRuntimes map[string][]string `toml:"runtimes"`
+	// RuntimeSupportsJSON is the list of the OCI runtimes that support --format=json
+	RuntimeSupportsJSON []string `toml:"runtime_supports_json"`
 	// RuntimePath is the path to OCI runtime binary for launching
 	// containers.
 	// The first path pointing to a valid file will be used
@@ -830,12 +832,21 @@ func makeRuntime(ctx context.Context, runtime *Runtime) (err error) {
 		}
 	}
 
+	supportsJSON := false
+	for _, r := range runtime.config.RuntimeSupportsJSON {
+		if r == runtime.config.OCIRuntime {
+			supportsJSON = true
+			break
+		}
+	}
+
 	// Make an OCI runtime to perform container operations
 	ociRuntime, err := newOCIRuntime(runtime.ociRuntimePath,
 		runtime.conmonPath, runtime.config.ConmonEnvVars,
 		runtime.config.CgroupManager, runtime.config.TmpDir,
 		runtime.config.MaxLogSize, runtime.config.NoPivotRoot,
-		runtime.config.EnablePortReservation)
+		runtime.config.EnablePortReservation,
+		supportsJSON)
 	if err != nil {
 		return err
 	}