utils: call GetRootlessRuntimeDir once

use a sync.Once to potentially avoid multiple system calls everytime
the function is called.

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

pkg/util/utils.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"syscall"
 	"time"
 
@@ -181,8 +182,16 @@ func ParseIDMapping(UIDMapSlice, GIDMapSlice []string, subUIDMap, subGIDMap stri
 	return &options, nil
 }
 
+var (
+	rootlessRuntimeDirOnce sync.Once
+	rootlessRuntimeDir     string
+)
+
 // GetRootlessRuntimeDir returns the runtime directory when running as non root
 func GetRootlessRuntimeDir() (string, error) {
+	var rootlessRuntimeDirError error
+
+	rootlessRuntimeDirOnce.Do(func() {
 		runtimeDir := os.Getenv("XDG_RUNTIME_DIR")
 		uid := fmt.Sprintf("%d", rootless.GetRootlessUID())
 		if runtimeDir == "" {
@@ -204,15 +213,23 @@ func GetRootlessRuntimeDir() (string, error) {
 		if runtimeDir == "" {
 			home := os.Getenv("HOME")
 			if home == "" {
-			return "", fmt.Errorf("neither XDG_RUNTIME_DIR nor HOME was set non-empty")
+				rootlessRuntimeDirError = fmt.Errorf("neither XDG_RUNTIME_DIR nor HOME was set non-empty")
+				return
 			}
 			resolvedHome, err := filepath.EvalSymlinks(home)
 			if err != nil {
-			return "", errors.Wrapf(err, "cannot resolve %s", home)
+				rootlessRuntimeDirError = errors.Wrapf(err, "cannot resolve %s", home)
+				return
 			}
 			runtimeDir = filepath.Join(resolvedHome, "rundir")
 		}
-	return runtimeDir, nil
+		rootlessRuntimeDir = runtimeDir
+	})
+
+	if rootlessRuntimeDirError != nil {
+		return "", rootlessRuntimeDirError
+	}
+	return rootlessRuntimeDir, nil
 }
 
 // GetRootlessDirInfo returns the parent path of where the storage for containers and