storage: Add reproducer for #201

At the moment, when using Code-Hex/vz like this:
```
f, err := os.OpenFile(devPath, open_flags, 0)
if err != nil {
	return nil, fmt.Errorf("error opening file: %v", err)
}

attachment, err := vz.NewDiskBlockDeviceStorageDeviceAttachment(f, conf.ReadOnly, vz.DiskSynchronizationModeFull)
if err != nil {
	_ = f.Close()
	return nil, fmt.Errorf("error creating disk attachment: %v", err)
}
```

the developer has to know that `f` must be kept alive at least as long as the disk attachment is in use. If not, `f` will be garbage collected, its file descriptor will be closed, and the attachment becomes invalid. In this situation, the virtualization framework would return an error.

This commit simply adds a test case exhibiting this problem. This will
be improved in the next commits.

Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>

Author: cfergeau

storage_test.go

@@ -2,7 +2,10 @@ package vz_test
 
 import (
 	"log"
+	"os"
+	"os/exec"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"testing"
 
@@ -103,3 +106,76 @@ func TestBlockDeviceWithCacheAndSyncMode(t *testing.T) {
 		t.Fatalf("want state %v but got %v", vz.VirtualMachineStateRunning, got)
 	}
 }
+
+func TestBlockDeviceWithDeviceAttachment(t *testing.T) {
+	if vz.Available(12) {
+		t.Skip("vz.NewDiskImageStorageDeviceAttachmentWithCacheAndSync is supported from macOS 12")
+	}
+
+	devPath := ""
+	container := newVirtualizationMachine(t,
+		func(vmc *vz.VirtualMachineConfiguration) error {
+			dir := t.TempDir()
+			path := filepath.Join(dir, "disk.img")
+			if err := vz.CreateDiskImage(path, 512); err != nil {
+				t.Fatal(err)
+			}
+			cmd := exec.Command("hdiutil", "attach", "-imagekey", "diskimage-class=CRawDiskImage", "-nomount", path)
+			output, err := cmd.Output()
+			if err != nil {
+				t.Fatalf("failed to attach disk image: %v", err)
+			}
+
+			outputStr := string(output)
+			lines := strings.Split(outputStr, "\n")
+			if len(lines) == 0 || !strings.HasPrefix(lines[0], "/dev/") {
+				log.Printf("[%s]\n", lines)
+				t.Fatalf("unexpected output from `hdiutil attach`")
+			}
+			if len(lines) != 0 && strings.HasPrefix(lines[0], "/dev/") {
+				devPath = strings.TrimSpace(lines[0])
+			}
+
+			var attachment *vz.DiskBlockDeviceStorageDeviceAttachment
+			{
+				dev, err := os.Open(devPath)
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				attachment, err = vz.NewDiskBlockDeviceStorageDeviceAttachment(dev, false, vz.DiskSynchronizationModeNone)
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+			// `dev` from the block above will be garbage collected and the underlying file descriptor will be closed.
+			// This will trigger an internal virtualization error in the subsequent code.
+			// https://github.com/Code-Hex/vz/issues/201
+			runtime.GC()
+
+			config, err := vz.NewVirtioBlockDeviceConfiguration(attachment)
+			if err != nil {
+				t.Fatal(err)
+			}
+			vmc.SetStorageDevicesVirtualMachineConfiguration([]vz.StorageDeviceConfiguration{
+				config,
+			})
+			return nil
+		},
+	)
+	t.Cleanup(func() {
+		if err := container.Shutdown(); err != nil {
+			log.Println(err)
+		}
+		cmd := exec.Command("hdiutil", "detach", devPath)
+		if err := cmd.Run(); err != nil {
+			log.Printf("hdiutil detach %s failed: %s\n", devPath, err)
+		}
+	})
+
+	vm := container.VirtualMachine
+
+	if got := vm.State(); vz.VirtualMachineStateRunning != got {
+		t.Fatalf("want state %v but got %v", vz.VirtualMachineStateRunning, got)
+	}
+}