[wip] run: Add --expand-root

I used this to test out CentOS/centos-bootc#394

But right now this leaks the disk; to fix that we need to use
`-add-fd` instead.

(This all conflicts with the libvirt stuff so putting it on the
 backburner)

cmd/run.go

@@ -17,6 +17,7 @@ type osVmConfig struct {
 	CloudInitDir    string
 	KsFile          string
 	Background      bool
+	ExpandRoot      uint
 	RemoveVm        bool // Kill the running VM when it exits
 	RemoveDiskImage bool // After exit of the VM, remove the disk image
 }
@@ -41,6 +42,8 @@ func init() {
 
 	runCmd.Flags().StringVar(&vmConfig.CloudInitDir, "cloudinit", "", "--cloudinit [[transport:]cloud-init data directory] (transport: cdrom | imds)")
 
+	runCmd.Flags().UintVar(&vmConfig.ExpandRoot, "expand-root", 0, "Add additional space to block device (size in GiB)")
+
 	runCmd.Flags().BoolVarP(&vmConfig.Background, "background", "B", false, "Do not spawn SSH, run in background")
 	runCmd.Flags().BoolVar(&vmConfig.RemoveVm, "rm", false, "Kill the running VM when it exits, requires --interactive")
 
@@ -75,7 +78,7 @@ func doRun(flags *cobra.Command, args []string) error {
 		return fmt.Errorf("ssh getFreeTcpPort: %w", err)
 	}
 
-	err = vm.Run(vmDir, sshPort, vmConfig.User, config.MachineSshKeyPriv, ciData, ciPort)
+	err = vm.Run(vmDir, sshPort, vmConfig.User, config.MachineSshKeyPriv, ciData, ciPort, vmConfig.ExpandRoot)
 	if err != nil {
 		return fmt.Errorf("runBootcVM: %w", err)
 	}

pkg/vm/run.go

@@ -36,7 +36,7 @@ func createQemuCommand() *exec.Cmd {
 	return exec.Command(path, args...)
 }
 
-func Run(vmDir string, sshPort int, user, sshIdentity string, ciData bool, ciPort int) error {
+func Run(vmDir string, sshPort int, user, sshIdentity string, ciData bool, ciPort int, expandRoot uint) error {
 	var args []string
 	args = append(args, "-cpu", "host")
 	args = append(args, "-m", "2G")
@@ -49,8 +49,26 @@ func Run(vmDir string, sshPort int, user, sshIdentity string, ciData bool, ciPor
 	vmPidFile := filepath.Join(vmDir, "run.pid")
 	args = append(args, "-pidfile", vmPidFile)
 
+	tempf, err := os.CreateTemp(vmDir, "tmpdisk")
+	if err != nil {
+		return err
+	}
+	diskPath := tempf.Name()
+	logrus.Debugf("Copying to %s", diskPath)
+	if err := tempf.Close(); err != nil {
+		return fmt.Errorf("failed to close: %w", err)
+	}
 	vmDiskImage := filepath.Join(vmDir, config.DiskImage)
-	driveCmd := fmt.Sprintf("if=virtio,format=raw,file=%s", vmDiskImage)
+	if err := exec.Command("cp", "--reflink=always", vmDiskImage, diskPath).Run(); err != nil {
+		return fmt.Errorf("failed to copy %s %s: %w", vmDiskImage, diskPath, err)
+	}
+	if expandRoot > 0 {
+		if err := exec.Command("truncate", "-s", fmt.Sprintf("%dG", expandRoot), diskPath).Run(); err != nil {
+			return fmt.Errorf("failed to expand disk: %w", err)
+		}
+	}
+
+	driveCmd := fmt.Sprintf("if=virtio,format=raw,file=%s", diskPath)
 	args = append(args, "-drive", driveCmd)
 	if ciData {
 		if ciPort != -1 {