feat: error out on qcow2 block devices

- Error out when qcow2 image is detected in block device validation

Author: vyasgun

cmd/vfkit/main.go

@@ -104,6 +104,10 @@ func newVMConfiguration(opts *cmdline.Options) (*config.VirtualMachine, error) {
 		return nil, err
 	}
 
+	if err := vmConfig.ValidBlkDevices(); err != nil {
+		return nil, err
+	}
+
 	if err := vmConfig.AddIgnitionFileFromCmdLine(opts.IgnitionPath); err != nil {
 		return nil, fmt.Errorf("failed to add ignition file: %w", err)
 	}

pkg/config/config.go

@@ -250,6 +250,32 @@ func (vm *VirtualMachine) AddIgnitionFileFromCmdLine(cmdlineOpts string) error {
 	return nil
 }
 
+func (vm *VirtualMachine) ValidBlkDevices() error {
+	for _, device := range vm.Devices {
+		switch device.(type) {
+		case *VirtioBlk:
+			dev := device.(*VirtioBlk)
+			imgPath := dev.ImagePath
+			if imgPath != "" {
+				file, err := os.Open(imgPath)
+				if err != nil {
+					return fmt.Errorf("failed to open file %s: %v", imgPath, err)
+				}
+				defer file.Close()
+				header := make([]byte, 4)
+				_, err = file.Read(header)
+				if err != nil {
+					return fmt.Errorf("failed to read the header of file %s: %v", imgPath, err)
+				}
+				if string(header) == "QFI\xfb" {
+					return fmt.Errorf("vfkit does not support qcow2 block devices")
+				}
+			}
+		}
+	}
+	return nil
+}
+
 func TimeSyncNew(vsockPort uint) (VMComponent, error) {
 
 	if vsockPort > math.MaxUint32 {

pkg/config/config_test.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"os"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -44,3 +45,28 @@ func TestNetworkBlockDevice_NoDevice(t *testing.T) {
 	nbdItem := vm.NetworkBlockDevice("nbd2")
 	require.Nil(t, nbdItem)
 }
+
+func TestVirtualMachine_ValidBlkDevices(t *testing.T) {
+	vm := &VirtualMachine{}
+
+	file, err := os.CreateTemp("", "test-*.img")
+	require.NoError(t, err)
+	defer os.Remove(file.Name())
+
+	// write qcow2 magic number
+	_, err = file.Write([]byte("QFI\xfb"))
+	require.NoError(t, err)
+
+	dev, err := VirtioBlkNew(file.Name())
+	require.NoError(t, err)
+	vm.Devices = append(vm.Devices, dev)
+
+	require.Error(t, vm.ValidBlkDevices())
+
+	// overwrite with non-qcow header
+	file.Seek(0, 0)
+	_, err = file.Write([]byte("NotQcow2"))
+	require.NoError(t, err)
+
+	require.NoError(t, vm.ValidBlkDevices())
+}