qemu: add fw_cfg flag to config

Signed-off-by: Salvatore Mazzarino <dev@mazzarino.cz>

qemu/qemu.go

@@ -2103,6 +2103,54 @@ type Kernel struct {
 	Params string
 }
 
+// FwCfg allows QEMU to pass entries to the guest
+// File and Str are mutually exclusive
+type FwCfg struct {
+	Name string
+	File string
+	Str  string
+}
+
+// Valid returns true if the FwCfg structure is valid and complete.
+func (fwcfg FwCfg) Valid() bool {
+	if fwcfg.Name == "" {
+		return false
+	}
+
+	if fwcfg.File != "" && fwcfg.Str != "" {
+		return false
+	}
+
+	if fwcfg.File == "" && fwcfg.Str == "" {
+		return false
+	}
+
+	return true
+}
+
+// QemuParams returns the qemu parameters built out of the FwCfg object
+func (fwcfg FwCfg) QemuParams(config *Config) []string {
+	var fwcfgParams []string
+	var qemuParams []string
+
+	if config.FwCfg.Name != "" {
+		fwcfgParams = append(fwcfgParams, fmt.Sprintf("name=%q", config.FwCfg.Name))
+
+		if config.FwCfg.File != "" {
+			fwcfgParams = append(fwcfgParams, fmt.Sprintf(",file=%q", config.FwCfg.File))
+		}
+
+		if config.FwCfg.Str != "" {
+			fwcfgParams = append(fwcfgParams, fmt.Sprintf(",string=%q", config.FwCfg.Str))
+		}
+	}
+
+	qemuParams = append(qemuParams, "-fw_cfg")
+	qemuParams = append(qemuParams, strings.Join(fwcfgParams, ""))
+
+	return qemuParams
+}
+
 // Knobs regroups a set of qemu boolean settings
 type Knobs struct {
 	// NoUserConfig prevents qemu from loading user config files.
@@ -2236,6 +2284,9 @@ type Config struct {
 	// fds is a list of open file descriptors to be passed to the spawned qemu process
 	fds []*os.File
 
+	// FwCfg is the -fw_cfg parameter
+	FwCfg FwCfg
+
 	IOThreads []IOThread
 
 	// PidFile is the -pidfile parameter
@@ -2568,6 +2619,19 @@ func (config *Config) appendLogFile() {
 	}
 }
 
+func (config *Config) appendFwCfg(logger QMPLog) {
+	if logger == nil {
+		logger = qmpNullLogger{}
+	}
+
+	if !config.FwCfg.Valid() {
+		logger.Errorf("fw_cfg is not valid: %+v", config.FwCfg)
+		return
+	}
+
+	config.qemuParams = append(config.qemuParams, config.FwCfg.QemuParams(config)...)
+}
+
 // LaunchQemu can be used to launch a new qemu instance.
 //
 // The Config parameter contains a set of qemu parameters and settings.
@@ -2595,6 +2659,7 @@ func LaunchQemu(config Config, logger QMPLog) (string, error) {
 	config.appendIncoming()
 	config.appendPidFile()
 	config.appendLogFile()
+	config.appendFwCfg(logger)
 
 	if err := config.appendCPUs(); err != nil {
 		return "", err