internal/systemd: simplify

Remove unused code and argument from the ActivationFiles,
and simplify its usage.

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

internal/third_party/systemd/activation/files_unix.go

@@ -33,22 +33,11 @@ const (
 	listenFdsStart = 3
 )
 
-// Files returns a slice containing a `os.File` object for each
+// Files returns a slice containing a os.File object for each
 // file descriptor passed to this process via systemd fd-passing protocol.
 //
 // The order of the file descriptors is preserved in the returned slice.
-// `unsetEnv` is typically set to `true` in order to avoid clashes in
-// fd usage and to avoid leaking environment flags to child processes.
-func Files(unsetEnv bool) []*os.File {
-	if unsetEnv {
-		defer func() {
-			// Unsetenv implementation for unix never returns an error.
-			_ = os.Unsetenv("LISTEN_PID")
-			_ = os.Unsetenv("LISTEN_FDS")
-			_ = os.Unsetenv("LISTEN_FDNAMES")
-		}()
-	}
-
+func Files() []*os.File {
 	pid, err := strconv.Atoi(os.Getenv("LISTEN_PID"))
 	if err != nil || pid != os.Getpid() {
 		return nil

utils_linux.go

@@ -399,17 +399,11 @@ func startContainer(context *cli.Context, action CtAct, criuOpts *libcontainer.C
 		}
 	}
 
-	// Support on-demand socket activation by passing file descriptors into the container init process.
-	listenFDs := []*os.File{}
-	if os.Getenv("LISTEN_FDS") != "" {
-		listenFDs = activation.Files(false)
-	}
-
 	r := &runner{
 		enableSubreaper: !context.Bool("no-subreaper"),
 		shouldDestroy:   !context.Bool("keep"),
 		container:       container,
-		listenFDs:       listenFDs,
+		listenFDs:       activation.Files(), // On-demand socket activation.
 		notifySocket:    notifySocket,
 		consoleSocket:   context.String("console-socket"),
 		pidfdSocket:     context.String("pidfd-socket"),