use string-concatenation instead of sprintf for simple cases

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

libcontainer/standard_init_linux.go

@@ -3,10 +3,10 @@
 package libcontainer
 
 import (
-	"fmt"
 	"os"
 	"os/exec"
 	"runtime"
+	"strconv"
 
 	"github.com/opencontainers/runc/libcontainer/apparmor"
 	"github.com/opencontainers/runc/libcontainer/configs"
@@ -40,7 +40,7 @@ func (l *linuxStandardInit) getSessionRingParams() (string, uint32, uint32) {
 
 	// Create a unique per session container name that we can join in setns;
 	// However, other containers can also join it.
-	return fmt.Sprintf("_ses.%s", l.config.ContainerId), 0xffffffff, newperms
+	return "_ses." + l.config.ContainerId, 0xffffffff, newperms
 }
 
 func (l *linuxStandardInit) Init() error {
@@ -185,7 +185,7 @@ func (l *linuxStandardInit) Init() error {
 	// user process. We open it through /proc/self/fd/$fd, because the fd that
 	// was given to us was an O_PATH fd to the fifo itself. Linux allows us to
 	// re-open an O_PATH fd through /proc.
-	fd, err := unix.Open(fmt.Sprintf("/proc/self/fd/%d", l.fifoFd), unix.O_WRONLY|unix.O_CLOEXEC, 0)
+	fd, err := unix.Open("/proc/self/fd/"+strconv.Itoa(l.fifoFd), unix.O_WRONLY|unix.O_CLOEXEC, 0)
 	if err != nil {
 		return newSystemErrorWithCause(err, "open exec fifo")
 	}