Error on HyperV VM start when gvproxy has failed to start

After the VM has successfully started, check that gvproxy is
still running. If it is not, throw an error and refuse to
complete machine start.

[NO NEW TESTS NEEDED] I don't think we can deliberately trigger a
bad gvproxy start without a bad Podman binary. We could try and
kill gvproxy after it starts but before the machine is booted but
that's very prone to races.

Slightly restructure code so that starting shares happens later
and has its own configuration write - so the VM is still recorded
as running if starting shares fails.

Signed-off-by: Matt Heon <mheon@redhat.com>

pkg/machine/hyperv/machine.go

@@ -27,6 +27,7 @@ import (
 	"github.com/containers/podman/v4/pkg/util"
 	"github.com/containers/podman/v4/utils"
 	"github.com/containers/storage/pkg/lockfile"
+	psutil "github.com/shirou/gopsutil/v3/process"
 	"github.com/sirupsen/logrus"
 )
 
@@ -578,7 +579,7 @@ func (m *HyperVMachine) Start(name string, opts machine.StartOptions) error {
 	if vm.State() != hypervctl.Disabled {
 		return hypervctl.ErrMachineStateInvalid
 	}
-	_, _, err = m.startHostNetworking()
+	gvproxyPid, _, _, err := m.startHostNetworking()
 	if err != nil {
 		return fmt.Errorf("unable to start host networking: %q", err)
 	}
@@ -601,10 +602,6 @@ func (m *HyperVMachine) Start(name string, opts machine.StartOptions) error {
 	// set starting back false now that we are running
 	m.Starting = false
 
-	if err := m.startShares(); err != nil {
-		return err
-	}
-
 	if m.HostUser.Modified {
 		if machine.UpdatePodmanDockerSockService(m, name, m.UID, m.Rootful) == nil {
 			// Reset modification state if there are no errors, otherwise ignore errors
@@ -612,8 +609,27 @@ func (m *HyperVMachine) Start(name string, opts machine.StartOptions) error {
 			m.HostUser.Modified = false
 		}
 	}
+
 	// Write the config with updated starting status and hostuser modification
-	return m.writeConfig()
+	if err := m.writeConfig(); err != nil {
+		return err
+	}
+
+	// Check if gvproxy is still running.
+	// Do this *after* we write config, so we have still recorded that the
+	// VM is actually running - to ensure that stopping the machine works as
+	// expected.
+	_, err = psutil.NewProcess(gvproxyPid)
+	if err != nil {
+		return fmt.Errorf("gvproxy appears to have stopped (PID %d): %w", gvproxyPid, err)
+	}
+
+	// Finalize starting shares after we are confident gvproxy is still alive.
+	if err := m.startShares(); err != nil {
+		return err
+	}
+
+	return nil
 }
 
 func (m *HyperVMachine) State(_ bool) (define.Status, error) {
@@ -735,24 +751,24 @@ func (m *HyperVMachine) loadHyperVMachineFromJSON(fqConfigPath string) error {
 	return json.Unmarshal(b, m)
 }
 
-func (m *HyperVMachine) startHostNetworking() (string, machine.APIForwardingState, error) {
+func (m *HyperVMachine) startHostNetworking() (int32, string, machine.APIForwardingState, error) {
 	var (
 		forwardSock string
 		state       machine.APIForwardingState
 	)
 	cfg, err := config.Default()
 	if err != nil {
-		return "", machine.NoForwarding, err
+		return -1, "", machine.NoForwarding, err
 	}
 
 	executable, err := os.Executable()
 	if err != nil {
-		return "", 0, fmt.Errorf("unable to locate executable: %w", err)
+		return -1, "", 0, fmt.Errorf("unable to locate executable: %w", err)
 	}
 
 	gvproxyBinary, err := cfg.FindHelperBinary("gvproxy.exe", false)
 	if err != nil {
-		return "", 0, err
+		return -1, "", 0, err
 	}
 
 	cmd := gvproxy.NewGvproxyCommand()
@@ -769,20 +785,20 @@ func (m *HyperVMachine) startHostNetworking() (string, machine.APIForwardingStat
 
 	if logrus.IsLevelEnabled(logrus.DebugLevel) {
 		if err := logCommandToFile(c, "gvproxy.log"); err != nil {
-			return "", 0, err
+			return -1, "", 0, err
 		}
 	}
 
 	logrus.Debugf("Starting gvproxy with command: %s %v", gvproxyBinary, c.Args)
 
 	if err := c.Start(); err != nil {
-		return "", 0, fmt.Errorf("unable to execute: %s: %w", cmd.ToCmdline(), err)
+		return -1, "", 0, fmt.Errorf("unable to execute: %s: %w", cmd.ToCmdline(), err)
 	}
 
 	logrus.Debugf("Got gvproxy PID as %d", c.Process.Pid)
 
 	if len(m.MountVsocks) == 0 {
-		return forwardSock, state, nil
+		return int32(c.Process.Pid), forwardSock, state, nil
 	}
 
 	// Start the 9p server in the background
@@ -807,17 +823,17 @@ func (m *HyperVMachine) startHostNetworking() (string, machine.APIForwardingStat
 
 	if logrus.IsLevelEnabled(logrus.DebugLevel) {
 		if err := logCommandToFile(fsCmd, "podman-machine-server9.log"); err != nil {
-			return "", 0, err
+			return -1, "", 0, err
 		}
 	}
 
 	if err := fsCmd.Start(); err != nil {
-		return "", 0, fmt.Errorf("unable to execute: %s %v: %w", executable, args, err)
+		return -1, "", 0, fmt.Errorf("unable to execute: %s %v: %w", executable, args, err)
 	}
 
 	logrus.Infof("Started podman 9p server as PID %d", fsCmd.Process.Pid)
 
-	return forwardSock, state, nil
+	return int32(c.Process.Pid), forwardSock, state, nil
 }
 
 func logCommandToFile(c *exec.Cmd, filename string) error {