Ensure HyperV 9p mounts work when a dir doesn't exist

Before, we required that the mount target exist and be a
directory for the 9p mount to successfully complete, which is not
how things are supposed to work - the user should be able to
mount anywhere. This should just be a simple mkdir, but with FCOS
the root directory is immutable so we need to undo that before we
can mkdir, and unfortunately we don't have a library that can do
chattr (and I didn't want to drag in a new dependency just for
that), so let's be gross and add it to the SSH command. I
aggressively dislike this but it does work.

[NO NEW TESTS NEEDED] Can worry about getting a more generic
mount test together for Machine later.

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

cmd/podman/machine/client9p.go

@@ -8,6 +8,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"strconv"
+	"time"
 
 	"github.com/containers/common/pkg/completion"
 	"github.com/containers/podman/v5/cmd/podman/registry"
@@ -69,8 +70,22 @@ func client9p(portNum uint32, mountPath string) error {
 
 	logrus.Infof("Going to mount 9p on vsock port %d to directory %s", portNum, mountPath)
 
-	// Host connects to non-hypervisor processes on the host running the VM.
-	conn, err := vsock.Dial(vsock.Host, portNum, nil)
+	// The server is starting at the same time.
+	// Perform up to 5 retries with a backoff.
+	var (
+		conn    *vsock.Conn
+		retries = 20
+	)
+	for i := 0; i < retries; i++ {
+		// Host connects to non-hypervisor processes on the host running the VM.
+		conn, err = vsock.Dial(vsock.Host, portNum, nil)
+		// If errors.Is worked on this error, we could detect non-timeout errors.
+		// But it doesn't. So retry 5 times regardless.
+		if err == nil {
+			break
+		}
+		time.Sleep(250 * time.Millisecond)
+	}
 	if err != nil {
 		return fmt.Errorf("dialing vsock port %d: %w", portNum, err)
 	}

pkg/machine/e2e/basic_test.go

@@ -1,10 +1,14 @@
 package e2e_test
 
 import (
+	"fmt"
 	"io"
 	"net"
 	"net/http"
 	"net/url"
+	"os"
+	"path"
+	"path/filepath"
 	"time"
 
 	. "github.com/onsi/ginkgo/v2"
@@ -93,6 +97,31 @@ var _ = Describe("run basic podman commands", func() {
 		Expect(out).ToNot(ContainSubstring("gvproxy"))
 	})
 
+	It("podman volume on non-standard path", func() {
+		skipIfWSL("Requires standard volume handling")
+		dir, err := os.MkdirTemp("", "machine-volume")
+		Expect(err).ToNot(HaveOccurred())
+		defer os.RemoveAll(dir)
+
+		testString := "abcdefg1234567"
+		testFile := "testfile"
+		err = os.WriteFile(filepath.Join(dir, testFile), []byte(testString), 0644)
+		Expect(err).ToNot(HaveOccurred())
+
+		name := randomString()
+		machinePath := "/does/not/exist"
+		init := new(initMachine).withVolume(fmt.Sprintf("%s:%s", dir, machinePath)).withImagePath(mb.imagePath).withNow()
+		session, err := mb.setName(name).setCmd(init).run()
+		Expect(err).ToNot(HaveOccurred())
+		Expect(session).To(Exit(0))
+
+		// Must use path.Join to ensure forward slashes are used, even on Windows.
+		ssh := new(sshMachine).withSSHCommand([]string{"cat", path.Join(machinePath, testFile)})
+		ls, err := mb.setName(name).setCmd(ssh).run()
+		Expect(err).ToNot(HaveOccurred())
+		Expect(ls).To(Exit(0))
+		Expect(ls.outputToString()).To(ContainSubstring(testString))
+	})
 })
 
 func testHTTPServer(port string, shouldErr bool, expectedResponse string) {

pkg/machine/hyperv/stubber.go

@@ -423,7 +423,7 @@ func (h HyperVStubber) PostStartNetworking(mc *vmconfigs.MachineConfig, noInfo b
 
 	for _, mount := range mc.Mounts {
 		if mount.VSockNumber == nil {
-			return fmt.Errorf("mount %s has not vsock port defined", mount.Source)
+			return fmt.Errorf("mount %s has no vsock port defined", mount.Source)
 		}
 		p9ServerArgs = append(p9ServerArgs, "--serve", fmt.Sprintf("%s:%s", mount.Source, winio.VsockServiceID(uint32(*mount.VSockNumber)).String()))
 	}

pkg/machine/hyperv/volumes.go

@@ -5,6 +5,8 @@ package hyperv
 import (
 	"errors"
 	"fmt"
+	"path"
+	"strings"
 
 	"github.com/containers/podman/v5/pkg/machine"
 	"github.com/containers/podman/v5/pkg/machine/hyperv/vsock"
@@ -40,7 +42,19 @@ func removeShares(mc *vmconfigs.MachineConfig) error {
 
 func startShares(mc *vmconfigs.MachineConfig) error {
 	for _, mount := range mc.Mounts {
-		args := []string{"-q", "--", "sudo", "podman"}
+		args := []string{"-q", "--"}
+
+		cleanTarget := path.Clean(mount.Target)
+		requiresChattr := !strings.HasPrefix(cleanTarget, "/home") && !strings.HasPrefix(cleanTarget, "/mnt")
+		if requiresChattr {
+			args = append(args, "sudo", "chattr", "-i", "/", "; ")
+		}
+		args = append(args, "sudo", "mkdir", "-p", cleanTarget, "; ")
+		if requiresChattr {
+			args = append(args, "sudo", "chattr", "+i", "/", "; ")
+		}
+
+		args = append(args, "sudo", "podman")
 		if logrus.IsLevelEnabled(logrus.DebugLevel) {
 			args = append(args, "--log-level=debug")
 		}
@@ -48,7 +62,7 @@ func startShares(mc *vmconfigs.MachineConfig) error {
 		if mount.VSockNumber == nil {
 			return errors.New("cannot start 9p shares with undefined vsock number")
 		}
-		args = append(args, "machine", "client9p", fmt.Sprintf("%d", mount.VSockNumber), mount.Target)
+		args = append(args, "machine", "client9p", fmt.Sprintf("%d", *mount.VSockNumber), mount.Target)
 
 		if err := machine.CommonSSH(mc.SSH.RemoteUsername, mc.SSH.IdentityPath, mc.Name, mc.SSH.Port, args); err != nil {
 			return err