internal/pkg: automatic overlay mount on work

This directly submits the upperdir to cache. It is primarily used in bootstrapping where tools are limited and should not be used unless there is a very good reason to.

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

internal/pkg/testdata/main.go

@@ -40,18 +40,25 @@ func main() {
 		log.Fatalf("Environ: %q, want %q", os.Environ(), wantEnv)
 	}
 
-	var overlayTmp bool
+	var overlayTmp, overlayWork bool
 	const (
-		wantExec        = "/opt/bin/testtool"
-		wantExecOverlay = "/tmp/bin/testtool"
+		wantExec     = "/opt/bin/testtool"
+		wantExecTmp  = "/tmp/bin/testtool"
+		wantExecWork = "/work/bin/testtool"
 	)
 	if got, err := os.Executable(); err != nil {
 		log.Fatalf("Executable: error = %v", err)
 	} else if got != wantExec {
-		if got != wantExecOverlay {
+		switch got {
+		case wantExecTmp:
+			overlayTmp = true
+
+		case wantExecWork:
+			overlayWork = true
+
+		default:
 			log.Fatalf("Executable: %q, want %q", got, wantExec)
 		}
-		overlayTmp = true
 	}
 
 	wantHostname := "cure"
@@ -153,8 +160,16 @@ func main() {
 	}
 
 	next()
-	if path.Base(m.Root) != ident || m.Target != "/work" {
-		log.Fatal("unexpected work mount entry")
+	if overlayWork {
+		ident = "VMCurZKCA_MV80zb-ZBWVytfl3rhYOKJeo2u9l-OuaytQ_w_r4EsqgJ2nfO93x5_"
+		if m.Root != "/" || m.Target != "/work" ||
+			m.Source != "overlay" || m.FsType != "overlay" {
+			log.Fatal("unexpected work mount entry")
+		}
+	} else {
+		if path.Base(m.Root) != ident || m.Target != "/work" {
+			log.Fatal("unexpected work mount entry")
+		}
 	}
 
 	if !overlayTmp {