init.go: move logger setup to StartInitialization

Currently, logrus is used from the Go part of runc init, mostly for a
few debug messages (see setns_init_linux.go and standard_init_linux.go),
and a single warning (see rootfs_linux.go).

This means logrus is part of init implementation, and thus, its setup
belongs to StartInitialization().

Move the code there. As a nice side effect, now we don't have to convert
_LIBCONTAINER_LOGPIPE twice.

Note that since this initialization is now also called from libct/int
tests, which do not set _LIBCONTAINER_LOGLEVEL, let's make
_LIBCONTAINER_LOGLEVEL optional.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

init.go

@@ -3,11 +3,9 @@ package main
 import (
 	"os"
 	"runtime"
-	"strconv"
 
 	"github.com/opencontainers/runc/libcontainer"
 	_ "github.com/opencontainers/runc/libcontainer/nsenter"
-	"github.com/sirupsen/logrus"
 )
 
 func init() {
@@ -17,21 +15,6 @@ func init() {
 		runtime.GOMAXPROCS(1)
 		runtime.LockOSThread()
 
-		level, err := strconv.Atoi(os.Getenv("_LIBCONTAINER_LOGLEVEL"))
-		if err != nil {
-			panic(err)
-		}
-
-		logPipeFd, err := strconv.Atoi(os.Getenv("_LIBCONTAINER_LOGPIPE"))
-		if err != nil {
-			panic(err)
-		}
-
-		logrus.SetLevel(logrus.Level(level))
-		logrus.SetOutput(os.NewFile(uintptr(logPipeFd), "logpipe"))
-		logrus.SetFormatter(new(logrus.JSONFormatter))
-		logrus.Debug("child process in init()")
-
 		if err := libcontainer.StartInitialization(); err != nil {
 			// as the error is sent back to the parent there is no need to log
 			// or write it to stderr because the parent process will handle this