native.go

/*
   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 native

import (
	"context"
	"fmt"
	"os"
	"path/filepath"

	"github.com/containerd/containerd/log"
	"github.com/containerd/containerd/mount"
	"github.com/containerd/containerd/snapshots"
	"github.com/containerd/containerd/snapshots/storage"

	"github.com/containerd/continuity/fs"
)

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

// NewSnapshotter returns a Snapshotter which copies layers on the underlying
// file system. A metadata file is stored under the root.
func NewSnapshotter(root string) (snapshots.Snapshotter, error) {
	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{
		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 (o *snapshotter) Stat(ctx context.Context, key string) (info snapshots.Info, err error) {
	err = o.ms.WithTransaction(ctx, false, func(ctx context.Context) error {
		_, info, _, err = storage.GetInfo(ctx, key)
		return err
	})
	if err != nil {
		return snapshots.Info{}, err
	}

	return info, nil
}

func (o *snapshotter) Update(ctx context.Context, info snapshots.Info, fieldpaths ...string) (_ snapshots.Info, err error) {
	err = o.ms.WithTransaction(ctx, true, func(ctx context.Context) error {
		info, err = storage.UpdateInfo(ctx, info, fieldpaths...)
		return err
	})
	if err != nil {
		return snapshots.Info{}, err
	}

	return info, nil
}

func (o *snapshotter) Usage(ctx context.Context, key string) (usage snapshots.Usage, err error) {
	var (
		id   string
		info snapshots.Info
	)

	err = o.ms.WithTransaction(ctx, false, func(ctx context.Context) error {
		id, info, usage, err = storage.GetInfo(ctx, key)
		return err
	})
	if err != nil {
		return snapshots.Usage{}, err
	}

	if info.Kind == snapshots.KindActive {
		du, err := fs.DiskUsage(ctx, o.getSnapshotDir(id))
		if err != nil {
			return snapshots.Usage{}, err
		}
		usage = snapshots.Usage(du)
	}

	return usage, nil
}

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

func (o *snapshotter) View(ctx context.Context, key, parent string, opts ...snapshots.Opt) ([]mount.Mount, error) {
	return o.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 (o *snapshotter) Mounts(ctx context.Context, key string) (_ []mount.Mount, err error) {
	var s storage.Snapshot
	err = o.ms.WithTransaction(ctx, false, func(ctx context.Context) error {
		s, err = storage.GetSnapshot(ctx, key)
		if err != nil {
			return fmt.Errorf("failed to get snapshot mount: %w", err)
		}

		return nil
	})
	if err != nil {
		return nil, err
	}

	return o.mounts(s), nil
}

func (o *snapshotter) Commit(ctx context.Context, name, key string, opts ...snapshots.Opt) error {
	return o.ms.WithTransaction(ctx, true, func(ctx context.Context) error {
		id, _, _, err := storage.GetInfo(ctx, key)
		if err != nil {
			return err
		}

		usage, err := fs.DiskUsage(ctx, o.getSnapshotDir(id))
		if err != nil {
			return err
		}

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

// Remove abandons the transaction identified by key. All resources
// associated with the key will be removed.
func (o *snapshotter) Remove(ctx context.Context, key string) (err error) {
	var (
		renamed, path string
		restore       bool
	)

	err = o.ms.WithTransaction(ctx, true, func(ctx context.Context) error {
		id, _, err := storage.Remove(ctx, key)
		if err != nil {
			return fmt.Errorf("failed to remove: %w", err)
		}

		path = o.getSnapshotDir(id)
		renamed = filepath.Join(o.root, "snapshots", "rm-"+id)
		if err = os.Rename(path, renamed); err != nil {
			if !os.IsNotExist(err) {
				return fmt.Errorf("failed to rename: %w", err)
			}
			renamed = ""
		}

		restore = true
		return nil
	})

	if err != nil {
		if renamed != "" && restore {
			if err1 := os.Rename(renamed, path); err1 != nil {
				// May cause inconsistent data on disk
				log.G(ctx).WithError(err1).WithField("path", renamed).Error("failed to rename after failed commit")
			}
		}
		return err
	}
	if renamed != "" {
		if err := os.RemoveAll(renamed); 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 (o *snapshotter) Walk(ctx context.Context, fn snapshots.WalkFunc, fs ...string) error {
	return o.ms.WithTransaction(ctx, false, func(ctx context.Context) error {
		return storage.WalkInfo(ctx, fn, fs...)
	})
}

func (o *snapshotter) createSnapshot(ctx context.Context, kind snapshots.Kind, key, parent string, opts []snapshots.Opt) (_ []mount.Mount, err error) {
	var (
		path, td string
		s        storage.Snapshot
	)

	if kind == snapshots.KindActive || parent == "" {
		td, err = os.MkdirTemp(filepath.Join(o.root, "snapshots"), "new-")
		if err != nil {
			return nil, fmt.Errorf("failed to create temp dir: %w", err)
		}
		if err := os.Chmod(td, 0755); err != nil {
			return nil, fmt.Errorf("failed to chmod %s to 0755: %w", td, err)
		}
		defer func() {
			if err != nil {
				if td != "" {
					if err1 := os.RemoveAll(td); err1 != nil {
						err = fmt.Errorf("remove failed: %v: %w", err1, err)
					}
				}
				if path != "" {
					if err1 := os.RemoveAll(path); err1 != nil {
						err = fmt.Errorf("failed to remove path: %v: %w", err1, err)
					}
				}
			}
		}()
	}

	err = o.ms.WithTransaction(ctx, true, func(ctx context.Context) error {
		s, err = storage.CreateSnapshot(ctx, kind, key, parent, opts...)
		if err != nil {
			return fmt.Errorf("failed to create snapshot: %w", err)
		}

		if td != "" {
			if len(s.ParentIDs) > 0 {
				parent := o.getSnapshotDir(s.ParentIDs[0])
				xattrErrorHandler := func(dst, src, xattrKey string, copyErr error) error {
					// security.* xattr cannot be copied in most cases (moby/buildkit#1189)
					log.G(ctx).WithError(copyErr).Debugf("failed to copy xattr %q", xattrKey)
					return nil
				}
				copyDirOpts := []fs.CopyDirOpt{
					fs.WithXAttrErrorHandler(xattrErrorHandler),
				}
				if err = fs.CopyDir(td, parent, copyDirOpts...); err != nil {
					return fmt.Errorf("copying of parent failed: %w", err)
				}
			}

			path = o.getSnapshotDir(s.ID)
			if err = os.Rename(td, path); err != nil {
				return fmt.Errorf("failed to rename: %w", err)
			}
			td = ""
		}

		return nil
	})
	if err != nil {
		return nil, err
	}

	return o.mounts(s), nil
}

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

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

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

	if len(s.ParentIDs) == 0 || s.Kind == snapshots.KindActive {
		source = o.getSnapshotDir(s.ID)
	} else {
		source = o.getSnapshotDir(s.ParentIDs[0])
	}

	return []mount.Mount{
		{
			Source:  source,
			Type:    mountType,
			Options: append(defaultMountOptions, roFlag),
		},
	}
}

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