system: optimise string formatting

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/fpkg/app.go

@@ -65,6 +65,7 @@ type appInfo struct {
 func (app *appInfo) toFst(pathSet *appPathSet, argv []string, flagDropShell bool) *fst.Config {
 	config := &fst.Config{
 		ID:   app.ID,
+		Path: argv[0],
 		Args: argv,
 		Confinement: fst.ConfinementConfig{
 			AppID:    app.AppID,

cmd/fpkg/with.go

@@ -16,7 +16,8 @@ func withNixDaemon(
 	app *appInfo, pathSet *appPathSet, dropShell bool, beforeFail func(),
 ) {
 	mustRunAppDropShell(ctx, updateConfig(&fst.Config{
-		ID: app.ID,
+		ID:   app.ID,
+		Path: shellPath,
 		Args: []string{shellPath, "-lc", "rm -f /nix/var/nix/daemon-socket/socket && " +
 			// start nix-daemon
 			"nix-daemon --store / & " +
@@ -64,6 +65,7 @@ func withCacheDir(
 	app *appInfo, pathSet *appPathSet, dropShell bool, beforeFail func()) {
 	mustRunAppDropShell(ctx, &fst.Config{
 		ID:   app.ID,
+		Path: shellPath,
 		Args: []string{shellPath, "-lc", strings.Join(command, " && ")},
 		Confinement: fst.ConfinementConfig{
 			AppID:    app.AppID,

sandbox/sequential.go

@@ -301,7 +301,15 @@ func (l *Symlink) apply(*Params) error {
 		return msg.WrapErr(syscall.EBADE,
 			fmt.Sprintf("path %q is not absolute", l[1]))
 	}
-	if err := os.Symlink(l[0], toSysroot(l[1])); err != nil {
+
+	target := toSysroot(l[1])
+	if err := ensureFile(target, 0444, 0755); err != nil {
+		return err
+	}
+	if err := os.Remove(target); err != nil {
+		return msg.WrapErr(err, err.Error())
+	}
+	if err := os.Symlink(l[0], target); err != nil {
 		return msg.WrapErr(err, err.Error())
 	}
 	return nil