vde: defer vnl validation until starting qemu

Fix #146

Signed-off-by: Akihiro Suda <[email protected]>

Author: AkihiroSuda

pkg/limayaml/validate.go

@@ -179,31 +179,31 @@ func validateNetwork(yNetwork Network) error {
 		// optionally with vde:// prefix.
 		if !strings.Contains(vde.VNL, "://") || strings.HasPrefix(vde.VNL, "vde://") {
 			vdeSwitch := strings.TrimPrefix(vde.VNL, "vde://")
-			fi, err := os.Stat(vdeSwitch)
-			if err != nil {
-				return fmt.Errorf("field `%s.vnl` %q failed stat: %w", field, vdeSwitch, err)
-			}
-			if fi.IsDir() {
-				/* Switch mode (vdeSwitch is dir, port != 65535) */
-				ctlSocket := filepath.Join(vdeSwitch, "ctl")
-				fi, err = os.Stat(ctlSocket)
-				if err != nil {
-					return fmt.Errorf("field `%s.vnl` control socket %q failed stat: %w", field, ctlSocket, err)
-				}
-				if fi.Mode()&os.ModeSocket == 0 {
-					return fmt.Errorf("field `%s.vnl` file %q is not a UNIX socket", field, ctlSocket)
-				}
-				if vde.SwitchPort == 65535 {
-					return fmt.Errorf("field `%s.vnl` points to a non-PTP switch, so the port number must not be 65535", field)
-				}
+			if fi, err := os.Stat(vdeSwitch); err != nil {
+				// negligible when the instance is stopped
+				logrus.WithError(err).Debugf("field `%s.vnl` %q failed stat", field, vdeSwitch)
 			} else {
-				/* PTP mode (vdeSwitch is socket, port == 65535) */
-				if fi.Mode()&os.ModeSocket == 0 {
-					return fmt.Errorf("field `%s.vnl` %q is not a directory nor a UNIX socket", field, vdeSwitch)
-				}
-				if vde.SwitchPort != 65535 {
-					return fmt.Errorf("field `%s.vnl` points to a PTP (switchless) socket %q, so the port number has to be 65535 (got %d)",
-						field, vdeSwitch, vde.SwitchPort)
+				if fi.IsDir() {
+					/* Switch mode (vdeSwitch is dir, port != 65535) */
+					ctlSocket := filepath.Join(vdeSwitch, "ctl")
+					// ErrNotExist during os.Stat(ctlSocket) can be ignored. ctlSocket does not need to exist until actually starting the VM
+					if fi, err = os.Stat(ctlSocket); err == nil {
+						if fi.Mode()&os.ModeSocket == 0 {
+							return fmt.Errorf("field `%s.vnl` file %q is not a UNIX socket", field, ctlSocket)
+						}
+					}
+					if vde.SwitchPort == 65535 {
+						return fmt.Errorf("field `%s.vnl` points to a non-PTP switch, so the port number must not be 65535", field)
+					}
+				} else {
+					/* PTP mode (vdeSwitch is socket, port == 65535) */
+					if fi.Mode()&os.ModeSocket == 0 {
+						return fmt.Errorf("field `%s.vnl` %q is not a directory nor a UNIX socket", field, vdeSwitch)
+					}
+					if vde.SwitchPort != 65535 {
+						return fmt.Errorf("field `%s.vnl` points to a PTP (switchless) socket %q, so the port number has to be 65535 (got %d)",
+							field, vdeSwitch, vde.SwitchPort)
+					}
 				}
 			}
 		} else if runtime.GOOS != "linux" {

pkg/qemu/qemu.go

@@ -207,6 +207,11 @@ func Cmdline(cfg Config) (string, []string, error) {
 		// VDE2 only accepts the latter form.
 		// VDE2 supports macOS but VDE4 does not yet, so we trim vde:// prefix here for VDE2 compatibility.
 		vdeSock := strings.TrimPrefix(vde.VNL, "vde://")
+		if !strings.Contains(vdeSock, "://") {
+			if _, err := os.Stat(vdeSock); err != nil {
+				return "", nil, fmt.Errorf("cannot use VNL %q: %w", vde.VNL, err)
+			}
+		}
 		args = append(args, "-netdev", fmt.Sprintf("vde,id=net%d,sock=%s", i+1, vdeSock))
 		args = append(args, "-device", fmt.Sprintf("virtio-net-pci,netdev=net%d,mac=%s", i+1, vde.MACAddress))
 	}