qemu: allow to create a stopped guest

When Knobs.Stopped is set, the guest CPU will not be started at startup.

Signed-off-by: Peng Tao <bergwolf@gmail.com>

qemu/qemu.go

@@ -1182,6 +1182,9 @@ type Knobs struct {
 	// Only active when Realtime is set to true
 	Mlock bool
 
+	// Stopped will not start guest CPU at startup
+	Stopped bool
+
 	// Realtime will enable realtime QEMU
 	Realtime bool
 }
@@ -1521,6 +1524,10 @@ func (config *Config) appendKnobs() {
 			config.qemuParams = append(config.qemuParams, "mlock=off")
 		}
 	}
+
+	if config.Knobs.Stopped == true {
+		config.qemuParams = append(config.qemuParams, "-S")
+	}
 }
 
 func (config *Config) appendBios() {

qemu/qemu_test.go

@@ -388,7 +388,7 @@ func TestAppendEmptyDevice(t *testing.T) {
 }
 
 func TestAppendKnobsAllTrue(t *testing.T) {
-	var knobsString = "-no-user-config -nodefaults -nographic -daemonize -realtime mlock=on"
+	var knobsString = "-no-user-config -nodefaults -nographic -daemonize -realtime mlock=on -S"
 	knobs := Knobs{
 		NoUserConfig:        true,
 		NoDefaults:          true,
@@ -399,6 +399,7 @@ func TestAppendKnobsAllTrue(t *testing.T) {
 		FileBackedMemShared: true,
 		Realtime:            true,
 		Mlock:               true,
+		Stopped:             true,
 	}
 
 	testAppend(knobs, knobsString, t)
@@ -415,6 +416,7 @@ func TestAppendKnobsAllFalse(t *testing.T) {
 		FileBackedMemShared: false,
 		Realtime:            false,
 		Mlock:               false,
+		Stopped:             false,
 	}
 
 	testAppend(knobs, knobsString, t)