containerd/snapshots/windows/windows.go

// +build windows

/*
   Copyright The containerd Authors.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package windows

import (
	"context"
	"encoding/json"
	"os"
	"path/filepath"
	"strings"
	"syscall"
	"unsafe"

	"github.com/Microsoft/hcsshim"
	"github.com/containerd/containerd/errdefs"
	"github.com/containerd/containerd/log"
	"github.com/containerd/containerd/mount"
	"github.com/containerd/containerd/plugin"
	"github.com/containerd/containerd/snapshots"
	"github.com/containerd/containerd/snapshots/storage"
	"github.com/containerd/continuity/fs"
	"github.com/pkg/errors"
	"golang.org/x/sys/windows"
)

func init() {
	plugin.Register(&plugin.Registration{
		Type: plugin.SnapshotPlugin,
		ID:   "windows",
		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
			return NewSnapshotter(ic.Root)
		},
	})
}

type snapshotter struct {
	root string
	info hcsshim.DriverInfo
	ms   *storage.MetaStore
}

// NewSnapshotter returns a new windows snapshotter
func NewSnapshotter(root string) (snapshots.Snapshotter, error) {
	fsType, err := getFileSystemType(root)
	if err != nil {
		return nil, err
	}
	if strings.ToLower(fsType) != "ntfs" {
		return nil, errors.Wrapf(errdefs.ErrInvalidArgument, "%s is not on an NTFS volume - only NTFS volumes are supported", root)
	}

	if err := os.MkdirAll(root, 0700); err != nil {
		return nil, err
	}
	ms, err := storage.NewMetaStore(filepath.Join(root, "metadata.db"))
	if err != nil {
		return nil, err
	}

	if err := os.Mkdir(filepath.Join(root, "snapshots"), 0700); err != nil && !os.IsExist(err) {
		return nil, err
	}

	return &snapshotter{
		info: hcsshim.DriverInfo{
			HomeDir: filepath.Join(root, "snapshots"),
		},
		root: root,
		ms:   ms,
	}, nil
}

// Stat returns the info for an active or committed snapshot by name or
// key.
//
// Should be used for parent resolution, existence checks and to discern
// the kind of snapshot.
func (s *snapshotter) Stat(ctx context.Context, key string) (snapshots.Info, error) {
	ctx, t, err := s.ms.TransactionContext(ctx, false)
	if err != nil {
		return snapshots.Info{}, err
	}
	defer t.Rollback()

	_, info, _, err := storage.GetInfo(ctx, key)
	return info, err
}

func (s *snapshotter) Update(ctx context.Context, info snapshots.Info, fieldpaths ...string) (snapshots.Info, error) {
	ctx, t, err := s.ms.TransactionContext(ctx, true)
	if err != nil {
		return snapshots.Info{}, err
	}
	defer t.Rollback()

	info, err = storage.UpdateInfo(ctx, info, fieldpaths...)
	if err != nil {
		return snapshots.Info{}, err
	}

	if err := t.Commit(); err != nil {
		return snapshots.Info{}, err
	}

	return info, nil
}

func (s *snapshotter) Usage(ctx context.Context, key string) (snapshots.Usage, error) {
	ctx, t, err := s.ms.TransactionContext(ctx, false)
	if err != nil {
		return snapshots.Usage{}, err
	}
	defer t.Rollback()

	_, info, usage, err := storage.GetInfo(ctx, key)
	if err != nil {
		return snapshots.Usage{}, err
	}

	if info.Kind == snapshots.KindActive {
		du := fs.Usage{
			Size: 0,
		}
		usage = snapshots.Usage(du)
	}

	return usage, nil
}

func (s *snapshotter) Prepare(ctx context.Context, key, parent string, opts ...snapshots.Opt) ([]mount.Mount, error) {
	return s.createSnapshot(ctx, snapshots.KindActive, key, parent, opts)
}

func (s *snapshotter) View(ctx context.Context, key, parent string, opts ...snapshots.Opt) ([]mount.Mount, error) {
	return s.createSnapshot(ctx, snapshots.KindView, key, parent, opts)
}

// Mounts returns the mounts for the transaction identified by key. Can be
// called on an read-write or readonly transaction.
//
// This can be used to recover mounts after calling View or Prepare.
func (s *snapshotter) Mounts(ctx context.Context, key string) ([]mount.Mount, error) {
	ctx, t, err := s.ms.TransactionContext(ctx, false)
	if err != nil {
		return nil, err
	}
	defer t.Rollback()

	snapshot, err := storage.GetSnapshot(ctx, key)
	if err != nil {
		return nil, errors.Wrap(err, "failed to get snapshot mount")
	}
	return s.mounts(snapshot), nil
}

func (s *snapshotter) Commit(ctx context.Context, name, key string, opts ...snapshots.Opt) error {
	ctx, t, err := s.ms.TransactionContext(ctx, true)
	if err != nil {
		return err
	}
	defer t.Rollback()

	usage := fs.Usage{
		Size: 0,
	}

	if _, err = storage.CommitActive(ctx, key, name, snapshots.Usage(usage), opts...); err != nil {
		return errors.Wrap(err, "failed to commit snapshot")
	}

	if err := t.Commit(); err != nil {
		return err
	}
	return nil
}

// Remove abandons the transaction identified by key. All resources
// associated with the key will be removed.
func (s *snapshotter) Remove(ctx context.Context, key string) error {
	ctx, t, err := s.ms.TransactionContext(ctx, true)
	if err != nil {
		return err
	}
	defer t.Rollback()

	id, _, err := storage.Remove(ctx, key)
	if err != nil {
		return errors.Wrap(err, "failed to remove")
	}

	path := s.getSnapshotDir(id)
	renamedID := "rm-" + id
	renamed := filepath.Join(s.root, "snapshots", renamedID)
	if err := os.Rename(path, renamed); err != nil && !os.IsNotExist(err) {
		return err
	}

	if err := t.Commit(); err != nil {
		if err1 := os.Rename(renamed, path); err1 != nil {
			// May cause inconsistent data on disk
			log.G(ctx).WithError(err1).WithField("path", renamed).Errorf("Failed to rename after failed commit")
		}
		return errors.Wrap(err, "failed to commit")
	}

	if err := hcsshim.DestroyLayer(s.info, renamedID); err != nil {
		// Must be cleaned up, any "rm-*" could be removed if no active transactions
		log.G(ctx).WithError(err).WithField("path", renamed).Warnf("Failed to remove root filesystem")
	}

	return nil
}

// Walk the committed snapshots.
func (s *snapshotter) Walk(ctx context.Context, fn func(context.Context, snapshots.Info) error) error {
	ctx, t, err := s.ms.TransactionContext(ctx, false)
	if err != nil {
		return err
	}
	defer t.Rollback()

	return storage.WalkInfo(ctx, fn)
}

// Close closes the snapshotter
func (s *snapshotter) Close() error {
	return s.ms.Close()
}

func (s *snapshotter) mounts(sn storage.Snapshot) []mount.Mount {
	var (
		roFlag           string
		source           string
		parentLayerPaths []string
	)

	if sn.Kind == snapshots.KindView {
		roFlag = "ro"
	} else {
		roFlag = "rw"
	}

	if len(sn.ParentIDs) == 0 || sn.Kind == snapshots.KindActive {
		source = s.getSnapshotDir(sn.ID)
		parentLayerPaths = s.parentIDsToParentPaths(sn.ParentIDs)
	} else {
		source = s.getSnapshotDir(sn.ParentIDs[0])
		parentLayerPaths = s.parentIDsToParentPaths(sn.ParentIDs[1:])
	}

	// error is not checked here, as a string array will never fail to Marshal
	parentLayersJSON, _ := json.Marshal(parentLayerPaths)
	parentLayersOption := mount.ParentLayerPathsFlag + string(parentLayersJSON)

	var mounts []mount.Mount
	mounts = append(mounts, mount.Mount{
		Source: source,
		Type:   "windows-layer",
		Options: []string{
			roFlag,
			parentLayersOption,
		},
	})

	return mounts
}

func (s *snapshotter) getSnapshotDir(id string) string {
	return filepath.Join(s.root, "snapshots", id)
}

func (s *snapshotter) createSnapshot(ctx context.Context, kind snapshots.Kind, key, parent string, opts []snapshots.Opt) ([]mount.Mount, error) {
	ctx, t, err := s.ms.TransactionContext(ctx, true)
	if err != nil {
		return nil, err
	}
	defer t.Rollback()

	newSnapshot, err := storage.CreateSnapshot(ctx, kind, key, parent, opts...)
	if err != nil {
		return nil, errors.Wrap(err, "failed to create snapshot")
	}

	if kind == snapshots.KindActive {
		parentLayerPaths := s.parentIDsToParentPaths(newSnapshot.ParentIDs)

		var parentPath string
		if len(parentLayerPaths) != 0 {
			parentPath = parentLayerPaths[0]
		}

		if err := hcsshim.CreateSandboxLayer(s.info, newSnapshot.ID, parentPath, parentLayerPaths); err != nil {
			return nil, errors.Wrap(err, "failed to create sandbox layer")
		}

		// TODO(darrenstahlmsft): Allow changing sandbox size
	}

	if err := t.Commit(); err != nil {
		return nil, errors.Wrap(err, "commit failed")
	}

	return s.mounts(newSnapshot), nil
}

func (s *snapshotter) parentIDsToParentPaths(parentIDs []string) []string {
	var parentLayerPaths []string
	for _, ID := range parentIDs {
		parentLayerPaths = append(parentLayerPaths, s.getSnapshotDir(ID))
	}
	return parentLayerPaths
}

// getFileSystemType obtains the type of a file system through GetVolumeInformation
// https://msdn.microsoft.com/en-us/library/windows/desktop/aa364993(v=vs.85).aspx
func getFileSystemType(path string) (fsType string, hr error) {
	drive := filepath.VolumeName(path)
	if len(drive) != 2 {
		return "", errors.New("getFileSystemType path must start with a drive letter")
	}

	var (
		modkernel32              = windows.NewLazySystemDLL("kernel32.dll")
		procGetVolumeInformation = modkernel32.NewProc("GetVolumeInformationW")
		buf                      = make([]uint16, 255)
		size                     = windows.MAX_PATH + 1
	)
	drive += `\`
	n := uintptr(unsafe.Pointer(nil))
	r0, _, _ := syscall.Syscall9(procGetVolumeInformation.Addr(), 8, uintptr(unsafe.Pointer(windows.StringToUTF16Ptr(drive))), n, n, n, n, n, uintptr(unsafe.Pointer(&buf[0])), uintptr(size), 0)
	if int32(r0) < 0 {
		hr = syscall.Errno(win32FromHresult(r0))
	}
	fsType = windows.UTF16ToString(buf)
	return
}

// win32FromHresult is a helper function to get the win32 error code from an HRESULT
func win32FromHresult(hr uintptr) uintptr {
	if hr&0x1fff0000 == 0x00070000 {
		return hr & 0xffff
	}
	return hr
}