cmd/debos: Add backend argument to choose fakemachine backend

Fakemachine now allows the virtualisation backend to be chosen when
creating the machine, so allow the backend to be chosen by the user.

Signed-off-by: Christopher Obbard <[email protected]>

cmd/debos/debos.go

@@ -59,6 +59,7 @@ func warnLocalhost(variable string, value string) {
 func main() {
 	context := debos.DebosContext { &debos.CommonContext{}, "", "" }
 	var options struct {
+		Backend       string            `short:"b" long:"fakemachine-backend" description:"Fakemachine backend to use" default:"auto"`
 		ArtifactDir   string            `long:"artifactdir" description:"Directory for packed archives and ostree repositories (default: current directory)"`
 		InternalImage string            `long:"internal-image" hidden:"true"`
 		TemplateVars  map[string]string `short:"t" long:"template-var" description:"Template variables (use -t VARIABLE:VALUE syntax)"`
@@ -94,8 +95,10 @@ func main() {
 	}()
 
 	parser := flags.NewParser(&options, flags.Default)
-	args, err := parser.Parse()
+	fakemachineBackends := parser.FindOptionByLongName("fakemachine-backend")
+	fakemachineBackends.Choices = fakemachine.BackendNames()
 
+	args, err := parser.Parse()
 	if err != nil {
 		flagsErr, ok := err.(*flags.Error)
 		if ok && flagsErr.Type == flags.ErrHelp {
@@ -112,6 +115,12 @@ func main() {
 		return
 	}
 
+	if options.DisableFakeMachine && options.Backend != "auto" {
+		log.Println("--disable-fakemachine and --fakemachine-backend are mutually exclusive")
+		exitcode = 1
+		return
+	}
+
 	// Set interactive shell binary only if '--debug-shell' options passed
 	if options.DebugShell {
 		context.DebugShell = options.Shell
@@ -140,12 +149,34 @@ func main() {
 		return
 	}
 
-	/* If fakemachine is supported the outer fake machine will never use the
+	/* If fakemachine is used the outer fake machine will never use the
 	 * scratchdir, so just set it to /scratch as a dummy to prevent the
-	 * outer debos creating a temporary direction */
-	if !options.DisableFakeMachine && (fakemachine.InMachine() || fakemachine.Supported()) {
-		context.Scratchdir = "/scratch"
+	 * outer debos creating a temporary directory */
+	context.Scratchdir = "/scratch"
+
+	var runInFakeMachine = true
+	var m *fakemachine.Machine
+	if options.DisableFakeMachine || fakemachine.InMachine() {
+		runInFakeMachine = false
 	} else {
+		// attempt to create a fakemachine
+		m, err = fakemachine.NewMachineWithBackend(options.Backend)
+		if err != nil {
+			log.Printf("error creating fakemachine: %v", err)
+
+			/* fallback to running on the host unless the user has chosen
+			 * a specific backend */
+			if options.Backend == "auto" {
+				runInFakeMachine = false
+			} else {
+				exitcode = 1
+				return
+			}
+		}
+	}
+
+	// if running on the host create a scratchdir
+	if !runInFakeMachine && !fakemachine.InMachine() {
 		log.Printf("fakemachine not supported, running on the host!")
 		cwd, _ := os.Getwd()
 		context.Scratchdir, err = ioutil.TempDir(cwd, ".debos-")
@@ -212,8 +243,7 @@ func main() {
 		return
 	}
 
-	if !options.DisableFakeMachine && !fakemachine.InMachine() && fakemachine.Supported() {
-		m := fakemachine.NewMachine()
+	if runInFakeMachine {
 		var args []string
 
 		if options.Memory == "" {