containerd/snapshots/overlay/overlay.go

// +build linux

/*
   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 overlay

import (
	"context"
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"strings"
	"syscall"

	"github.com/containerd/containerd/log"
	"github.com/containerd/containerd/mount"
	"github.com/containerd/containerd/platforms"
	"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"
)

func init() {
	plugin.Register(&plugin.Registration{
		Type: plugin.SnapshotPlugin,
		ID:   "overlayfs",
		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
			ic.Meta.Platforms = append(ic.Meta.Platforms, platforms.DefaultSpec())
			ic.Meta.Exports["root"] = ic.Root
			return NewSnapshotter(ic.Root)
		},
	})
}

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

// NewSnapshotter returns a Snapshotter which uses overlayfs. The overlayfs
// diffs are stored under the provided root. 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
	}
	supportsDType, err := fs.SupportsDType(root)
	if err != nil {
		return nil, err
	}
	if !supportsDType {
		return nil, fmt.Errorf("%s does not support d_type. If the backing filesystem is xfs, please reformat with ftype=1 to enable d_type support", root)
	}
	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) (snapshots.Info, error) {
	ctx, t, err := o.ms.TransactionContext(ctx, false)
	if err != nil {
		return snapshots.Info{}, err
	}
	defer t.Rollback()
	_, info, _, err := storage.GetInfo(ctx, key)
	if err != nil {
		return snapshots.Info{}, err
	}

	return info, nil
}

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

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

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

	return info, nil
}

// Usage returns the resources taken by the snapshot identified by key.
//
// For active snapshots, this will scan the usage of the overlay "diff" (aka
// "upper") directory and may take some time.
//
// For committed snapshots, the value is returned from the metadata database.
func (o *snapshotter) Usage(ctx context.Context, key string) (snapshots.Usage, error) {
	ctx, t, err := o.ms.TransactionContext(ctx, false)
	if err != nil {
		return snapshots.Usage{}, err
	}
	id, info, usage, err := storage.GetInfo(ctx, key)
	t.Rollback() // transaction no longer needed at this point.

	if err != nil {
		return snapshots.Usage{}, err
	}

	upperPath := o.upperPath(id)

	if info.Kind == snapshots.KindActive {
		du, err := fs.DiskUsage(upperPath)
		if err != nil {
			// TODO(stevvooe): Consider not reporting an error in this case.
			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, error) {
	ctx, t, err := o.ms.TransactionContext(ctx, false)
	if err != nil {
		return nil, err
	}
	s, err := storage.GetSnapshot(ctx, key)
	t.Rollback()
	if err != nil {
		return nil, errors.Wrap(err, "failed to get active mount")
	}
	return o.mounts(s), nil
}

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

	defer func() {
		if err != nil {
			if rerr := t.Rollback(); rerr != nil {
				log.G(ctx).WithError(rerr).Warn("failed to rollback transaction")
			}
		}
	}()

	// grab the existing id
	id, _, _, err := storage.GetInfo(ctx, key)
	if err != nil {
		return err
	}

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

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

// 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) {
	ctx, t, err := o.ms.TransactionContext(ctx, true)
	if err != nil {
		return err
	}
	defer func() {
		if err != nil && t != nil {
			if rerr := t.Rollback(); rerr != nil {
				log.G(ctx).WithError(rerr).Warn("failed to rollback transaction")
			}
		}
	}()

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

	path := filepath.Join(o.root, "snapshots", id)
	renamed := filepath.Join(o.root, "snapshots", "rm-"+id)
	if err := os.Rename(path, renamed); err != nil {
		return errors.Wrap(err, "failed to rename")
	}

	err = t.Commit()
	t = nil
	if 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 := 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 func(context.Context, snapshots.Info) error) error {
	ctx, t, err := o.ms.TransactionContext(ctx, false)
	if err != nil {
		return err
	}
	defer t.Rollback()
	return storage.WalkInfo(ctx, fn)
}

func (o *snapshotter) createSnapshot(ctx context.Context, kind snapshots.Kind, key, parent string, opts []snapshots.Opt) ([]mount.Mount, error) {
	var (
		path        string
		snapshotDir = filepath.Join(o.root, "snapshots")
	)

	td, err := ioutil.TempDir(snapshotDir, "new-")
	if err != nil {
		return nil, errors.Wrap(err, "failed to create temp dir")
	}
	defer func() {
		if err != nil {
			if td != "" {
				if err1 := os.RemoveAll(td); err1 != nil {
					err = errors.Wrapf(err, "remove failed: %v", err1)
				}
			}
			if path != "" {
				if err1 := os.RemoveAll(path); err1 != nil {
					err = errors.Wrapf(err, "failed to remove path: %v", err1)
				}
			}
		}
	}()

	fs := filepath.Join(td, "fs")
	if err = os.MkdirAll(fs, 0755); err != nil {
		return nil, err
	}

	if kind == snapshots.KindActive {
		if err = os.MkdirAll(filepath.Join(td, "work"), 0711); err != nil {
			return nil, err
		}
	}

	ctx, t, err := o.ms.TransactionContext(ctx, true)
	if err != nil {
		return nil, err
	}
	rollback := true
	defer func() {
		if rollback {
			if rerr := t.Rollback(); rerr != nil {
				log.G(ctx).WithError(rerr).Warn("failed to rollback transaction")
			}
		}
	}()

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

	if len(s.ParentIDs) > 0 {
		st, err := os.Stat(o.upperPath(s.ParentIDs[0]))
		if err != nil {
			return nil, errors.Wrap(err, "failed to stat parent")
		}

		stat := st.Sys().(*syscall.Stat_t)
		if err := os.Lchown(fs, int(stat.Uid), int(stat.Gid)); err != nil {
			return nil, errors.Wrap(err, "failed to chown")
		}
	}

	path = filepath.Join(snapshotDir, s.ID)
	if err = os.Rename(td, path); err != nil {
		return nil, errors.Wrap(err, "failed to rename")
	}
	td = ""

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

	return o.mounts(s), nil
}

func (o *snapshotter) mounts(s storage.Snapshot) []mount.Mount {
	if len(s.ParentIDs) == 0 {
		// if we only have one layer/no parents then just return a bind mount as overlay
		// will not work
		roFlag := "rw"
		if s.Kind == snapshots.KindView {
			roFlag = "ro"
		}

		return []mount.Mount{
			{
				Source: o.upperPath(s.ID),
				Type:   "bind",
				Options: []string{
					roFlag,
					"rbind",
				},
			},
		}
	}
	var options []string

	if s.Kind == snapshots.KindActive {
		options = append(options,
			fmt.Sprintf("workdir=%s", o.workPath(s.ID)),
			fmt.Sprintf("upperdir=%s", o.upperPath(s.ID)),
		)
	} else if len(s.ParentIDs) == 1 {
		return []mount.Mount{
			{
				Source: o.upperPath(s.ParentIDs[0]),
				Type:   "bind",
				Options: []string{
					"ro",
					"rbind",
				},
			},
		}
	}

	parentPaths := make([]string, len(s.ParentIDs))
	for i := range s.ParentIDs {
		parentPaths[i] = o.upperPath(s.ParentIDs[i])
	}

	options = append(options, fmt.Sprintf("lowerdir=%s", strings.Join(parentPaths, ":")))
	return []mount.Mount{
		{
			Type:    "overlay",
			Source:  "overlay",
			Options: options,
		},
	}

}

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

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

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