shimv2: discard log before shim init log output

containerd would like to get the shim's socket
address from shimv2's stdout, thus it's better
to discard the log's output before shimv2 init
it's logger and at the same time add a hook to
log into syslog.

Fixes: #1035

Signed-off-by: Fupan Li <[email protected]>

containerd-shim-v2/service.go

@@ -8,6 +8,7 @@ package containerdshim
 import (
 	"context"
 	"encoding/json"
+	"io/ioutil"
 	"os"
 	sysexec "os/exec"
 	"path/filepath"
@@ -56,9 +57,13 @@ var vci vc.VC = &vc.VCImpl{}
 // New returns a new shim service that can be used via GRPC
 func New(ctx context.Context, id string, publisher events.Publisher) (cdshim.Shim, error) {
 	logger := logrus.WithField("ID", id)
+	// Discard the log before shim init its log output. Otherwise
+	// it will output into stdio, from which containerd would like
+	// to get the shim's socket address.
+	logrus.SetOutput(ioutil.Discard)
 	vci.SetLogger(ctx, logger)
 	katautils.SetLogger(ctx, logger, logger.Logger.Level)
-	_, runtimeConfig, err := katautils.LoadConfiguration("", true, true)
+	_, runtimeConfig, err := katautils.LoadConfiguration("", false, true)
 	if err != nil {
 		return nil, err
 	}