qemu: Add support for legacy serial device

- Add support for legacy serial device
- Additionally add support for the file backend for chardev

Legacy serial plus char backend file will allow us to support
capture early boot messages.

Signed-off-by: Manohar Castelino <mcastelino@apple.com>

qemu/qemu.go

@@ -66,6 +66,9 @@ type Device interface {
 type DeviceDriver string
 
 const (
+	// LegacySerial is the legacy serial device driver
+	LegacySerial DeviceDriver = "serial"
+
 	// NVDIMM is the Non Volatile DIMM device driver.
 	NVDIMM DeviceDriver = "nvdimm"
 
@@ -549,6 +552,9 @@ const (
 
 	// PTY creates a new pseudo-terminal on the host and connect to it.
 	PTY CharDeviceBackend = "pty"
+
+	// File sends traffic from the guest to a file on the host.
+	File CharDeviceBackend = "file"
 )
 
 // CharDevice represents a qemu character device.
@@ -637,8 +643,11 @@ func (cdev CharDevice) QemuParams(config *Config) []string {
 		cdevParams = append(cdevParams, fmt.Sprintf("path=%s", cdev.Path))
 	}
 
-	qemuParams = append(qemuParams, "-device")
-	qemuParams = append(qemuParams, strings.Join(deviceParams, ","))
+	// Legacy serial is special. It does not follow the device + driver model
+	if cdev.Driver != LegacySerial {
+		qemuParams = append(qemuParams, "-device")
+		qemuParams = append(qemuParams, strings.Join(deviceParams, ","))
+	}
 
 	qemuParams = append(qemuParams, "-chardev")
 	qemuParams = append(qemuParams, strings.Join(cdevParams, ","))
@@ -978,6 +987,43 @@ func (netdev NetDevice) QemuParams(config *Config) []string {
 	return qemuParams
 }
 
+// LegacySerialDevice represents a qemu legacy serial device.
+type LegacySerialDevice struct {
+	// ID is the serial device identifier.
+	// This maps to the char dev associated with the device
+	// as serial does not have a notion of id
+	// e.g:
+	// -chardev stdio,id=char0,mux=on,logfile=serial.log,signal=off -serial chardev:char0
+	// -chardev file,id=char0,path=serial.log -serial chardev:char0
+	Chardev string
+}
+
+// Valid returns true if the LegacySerialDevice structure is valid and complete.
+func (dev LegacySerialDevice) Valid() bool {
+	return dev.Chardev != ""
+}
+
+// QemuParams returns the qemu parameters built out of this serial device.
+func (dev LegacySerialDevice) QemuParams(config *Config) []string {
+	var deviceParam string
+	var qemuParams []string
+
+	deviceParam = fmt.Sprintf("chardev:%s", dev.Chardev)
+
+	qemuParams = append(qemuParams, "-serial")
+	qemuParams = append(qemuParams, deviceParam)
+
+	return qemuParams
+}
+
+/* Not used currently
+// deviceName returns the QEMU device name for the current combination of
+// driver and transport.
+func (dev LegacySerialDevice) deviceName(config *Config) string {
+	return dev.Chardev
+}
+*/
+
 // SerialDevice represents a qemu serial device.
 type SerialDevice struct {
 	// Driver is the qemu device driver

qemu/qemu_test.go

@@ -274,6 +274,28 @@ func TestAppendDeviceNetworkPCIMq(t *testing.T) {
 	testAppend(netdev, deviceNetworkPCIStringMq, t)
 }
 
+var deviceLegacySerialString = "-serial chardev:tlserial0"
+
+func TestAppendLegacySerial(t *testing.T) {
+	sdev := LegacySerialDevice{
+		Chardev: "tlserial0",
+	}
+
+	testAppend(sdev, deviceLegacySerialString, t)
+}
+
+var deviceLegacySerialPortString = "-chardev file,id=char0,path=/tmp/serial.log"
+
+func TestAppendDeviceLegacySerialPort(t *testing.T) {
+	chardev := CharDevice{
+		Driver:  LegacySerial,
+		Backend: File,
+		ID:      "char0",
+		Path:    "/tmp/serial.log",
+	}
+	testAppend(chardev, deviceLegacySerialPortString, t)
+}
+
 func TestAppendDeviceSerial(t *testing.T) {
 	sdev := SerialDevice{
 		Driver:        VirtioSerial,