image.go

package qemu

import (
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"strconv"
	"time"
)

const (
	ImageFormatRAW   = "raw"
	ImageFormatCLOOP = "cloop"
	ImageFormatCOW   = "cow"
	ImageFormatQCOW  = "qcow"
	ImageFormatQCOW2 = "qcow2"
	ImageFormatVDMK  = "vdmk"
	ImageFormatVDI   = "vdi"
	ImageFormatVHDX  = "vhdx"
	ImageFormatVPC   = "vpc"
)

// Image represents a QEMU disk image
type Image struct {
	Path   string // Image location (file)
	Format string // Image format
	Size   uint64 // Image size in bytes

	backingFile string
	snapshots   []Snapshot
}

// Snapshot represents a QEMU image snapshot
// Snapshots are snapshots of the complete virtual machine including CPU state
// RAM, device state and the content of all the writable disks
type Snapshot struct {
	ID      int
	Name    string
	Date    time.Time
	VMClock time.Time
}

// NewImage constructs a new Image data structure based
// on the specified parameters
func NewImage(path, format string, size uint64) Image {
	var img Image
	img.Path = path
	img.Format = format
	img.Size = size

	return img
}

// OpenImage retreives the information of the specified image
// file into an Image data structure
func OpenImage(path string) (Image, error) {
	var img Image

	if _, err := os.Stat(path); os.IsNotExist(err) {
		return img, err
	}

	img.Path = path

	err := img.retreiveInfos()
	if err != nil {
		return img, err
	}

	return img, nil
}

func (i *Image) retreiveInfos() error {
	type snapshotInfo struct {
		ID        string `json:"id"`
		Name      string `json:"name"`
		DateSec   int64  `json:"date-sec"`
		DateNsec  int64  `json:"date-nsec"`
		ClockSec  int64  `json:"vm-clock-sec"`
		ClockNsec int64  `json:"vm-clock-nsec"`
	}

	type imgInfo struct {
		Snapshots []snapshotInfo `json:"snapshots"`

		Format string `json:"format"`
		Size   uint64 `json:"virtual-size"`
	}

	var info imgInfo

	cmd := exec.Command("qemu-img", "info", "--output=json", i.Path)

	out, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("'qemu-img info' output: %s", oneLine(out))
	}

	err = json.Unmarshal(out, &info)
	if err != nil {
		return fmt.Errorf("'qemu-img info' invalid json output")
	}

	i.Format = info.Format
	i.Size = info.Size

	i.snapshots = make([]Snapshot, 0)
	for _, snap := range info.Snapshots {
		var s Snapshot

		id, err := strconv.Atoi(snap.ID)
		if err != nil {
			continue
		}

		s.ID = id
		s.Name = snap.Name
		s.Date = time.Unix(snap.DateSec, snap.DateNsec)
		s.VMClock = time.Unix(snap.ClockSec, snap.ClockNsec)

		i.snapshots = append(i.snapshots, s)
	}

	return nil
}

// Snapshots returns the snapshots contained
// within the image
func (i Image) Snapshots() ([]Snapshot, error) {
	err := i.retreiveInfos()
	if err != nil {
		return nil, err
	}

	if len(i.snapshots) == 0 {
		return make([]Snapshot, 0), nil
	}

	return i.snapshots, nil
}

// CreateSnapshot creates a snapshot of the image
// with the specified name
func (i *Image) CreateSnapshot(name string) error {
	cmd := exec.Command("qemu-img", "snapshot", "-c", name, i.Path)

	out, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("'qemu-img snapshot' output: %s", oneLine(out))
	}

	return nil
}

// RestoreSnapshot restores the the image to the
// specified snapshot name
func (i Image) RestoreSnapshot(name string) error {
	cmd := exec.Command("qemu-img", "snapshot", "-a", name, i.Path)

	out, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("'qemu-img snapshot' output: %s", oneLine(out))
	}

	return nil
}

// DeleteSnapshot deletes the the corresponding
// snapshot from the image
func (i Image) DeleteSnapshot(name string) error {
	cmd := exec.Command("qemu-img", "snapshot", "-d", name, i.Path)

	out, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("'qemu-img snapshot' output: %s", oneLine(out))
	}

	return nil
}

// SetBackingFile sets a backing file for the image
// If it is specified, the image will only record the
// differences from the backing file
func (i *Image) SetBackingFile(backingFile string) error {
	if _, err := os.Stat(backingFile); os.IsNotExist(err) {
		return err
	}

	i.backingFile = backingFile
	return nil
}

// Create actually creates the image based on the Image structure
// using the 'qemu-img create' command
func (i Image) Create() error {
	args := []string{"create", "-f", i.Format}

	if len(i.backingFile) > 0 {
		args = append(args, "-o")
		args = append(args, fmt.Sprintf("backing_file=%s", i.backingFile))
	}

	args = append(args, i.Path)
	args = append(args, strconv.FormatUint(i.Size, 10))

	cmd := exec.Command("qemu-img", args...)

	out, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("'qemu-img create' output: %s", oneLine(out))
	}

	return nil
}

// Rebase changes the backing file of the image
// to the specified file path
func (i *Image) Rebase(backingFile string) error {
	i.backingFile = backingFile

	cmd := exec.Command("qemu-img", "rebase", "-b", backingFile, i.Path)

	out, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("'qemu-img rebase' output: %s", oneLine(out))
	}

	return nil
}