Add qemu virtiofs command line option

Enables support for C version of virtiofs
A qemu option allows to specify virtiofsd path.
config.StatePath is used for storing the virtiofs sockets
Note that virtiofsd requires to start as root

Signed-off-by: Frédéric Dalleau <frederic.dalleau@docker.com>

src/cmd/linuxkit/run_qemu.go

@@ -45,6 +45,8 @@ type QemuConfig struct {
 	UUID             uuid.UUID
 	USB              bool
 	Devices          []string
+	VirtiofsdBinPath string
+	VirtiofsShares   []string
 }
 
 const (
@@ -136,6 +138,8 @@ func runQEMUCmd() *cobra.Command {
 		usbEnabled     bool
 		deviceFlags    multipleFlag
 		publishFlags   multipleFlag
+		virtiofsdCmd   string
+		virtiofsShares []string
 	)
 
 	cmd := &cobra.Command{
@@ -300,13 +304,22 @@ func runQEMUCmd() *cobra.Command {
 				UUID:             vmUUID,
 				USB:              usbEnabled,
 				Devices:          deviceFlags,
+				VirtiofsdBinPath: virtiofsdCmd,
+				VirtiofsShares:   virtiofsShares,
 			}
 
-			config, err = discoverBinaries(config)
+			config, err = discoverQemu(config)
 			if err != nil {
 				return err
 			}
 
+			if len(config.VirtiofsShares) > 0 {
+				config, err = discoverVirtiofsd(config)
+				if err != nil {
+					return err
+				}
+			}
+
 			if err = runQemuLocal(config); err != nil {
 				return err
 			}
@@ -351,6 +364,10 @@ func runQEMUCmd() *cobra.Command {
 	cmd.Flags().BoolVar(&usbEnabled, "usb", false, "Enable USB controller")
 	cmd.Flags().Var(&deviceFlags, "device", "Add USB host device(s). Format driver[,prop=value][,...] -- add device, like -device on the qemu command line.")
 
+	// Filesystems
+	cmd.Flags().StringVar(&virtiofsdCmd, "virtiofsd", "", "Path to virtiofsd binary (otherwise look in /usr/lib/qemu and /usr/local/lib/qemu)")
+	cmd.Flags().StringArrayVar(&virtiofsShares, "virtiofs", []string{}, "Directory shared on virtiofs")
+
 	return cmd
 }
 
@@ -398,6 +415,25 @@ func runQemuLocal(config QemuConfig) error {
 		return fmt.Errorf("Detached mode is only supported when running in a container, not locally")
 	}
 
+	if len(config.VirtiofsShares) > 0 {
+		args = append(args, "-object", "memory-backend-memfd,id=mem,size="+config.Memory+"M,share=on", "-numa", "node,memdev=mem")
+	}
+	for index, source := range config.VirtiofsShares {
+		socket := filepath.Join(config.StatePath, fmt.Sprintf("%s%d", "virtiofs", index))
+
+		cmd := exec.Command(config.VirtiofsdBinPath,
+			"--socket-path="+socket,
+			"-o", fmt.Sprintf("source=%s", source))
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		if err := cmd.Start(); err != nil {
+			return fmt.Errorf("virtiofs server cannot start: %v", err)
+		}
+		args = append(args, "-chardev", fmt.Sprintf("socket,id=char%d,path=%s", index, socket))
+		args = append(args, "-device",
+			fmt.Sprintf("vhost-user-fs-pci,chardev=char%d,tag=virtiofs%d", index, index))
+	}
+
 	qemuCmd := exec.Command(config.QemuBinPath, args...)
 	// If verbosity is enabled print out the full path/arguments
 	log.Debugf("%v\n", qemuCmd.Args)
@@ -589,7 +625,7 @@ func buildQemuCmdline(config QemuConfig) (QemuConfig, []string) {
 	return config, qemuArgs
 }
 
-func discoverBinaries(config QemuConfig) (QemuConfig, error) {
+func discoverQemu(config QemuConfig) (QemuConfig, error) {
 	if config.QemuImgPath != "" {
 		return config, nil
 	}
@@ -611,6 +647,16 @@ func discoverBinaries(config QemuConfig) (QemuConfig, error) {
 	return config, nil
 }
 
+func discoverVirtiofsd(config QemuConfig) (QemuConfig, error) {
+	if config.VirtiofsdBinPath != "" {
+		return config, nil
+	}
+
+	virtiofsdPath := filepath.Dir(config.QemuBinPath)
+	config.VirtiofsdBinPath = filepath.Join(virtiofsdPath, "..", "lib", "qemu", "virtiofsd")
+	return config, nil
+}
+
 func buildQemuForwardings(publishFlags multipleFlag) (string, error) {
 	if len(publishFlags) == 0 {
 		return "", nil