containerd/snapshots/btrfs/btrfs.go

// +build linux,!no_btrfs

/*
   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 btrfs

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

	"github.com/containerd/btrfs"
	"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"

	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
)

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

type snapshotter struct {
	device string // device of the root
	root   string // root provides paths for internal storage.
	ms     *storage.MetaStore
}

// NewSnapshotter returns a Snapshotter using btrfs. Uses the provided
// root directory for snapshots and stores the metadata in
// a file in the provided root.
// root needs to be a mount point of btrfs.
func NewSnapshotter(root string) (snapshots.Snapshotter, error) {
	// If directory does not exist, create it
	if _, err := os.Stat(root); err != nil {
		if !os.IsNotExist(err) {
			return nil, err
		}
		if err := os.Mkdir(root, 0755); err != nil {
			return nil, err
		}
	}

	mnt, err := mount.Lookup(root)
	if err != nil {
		return nil, err
	}
	if mnt.FSType != "btrfs" {
		return nil, fmt.Errorf("path %s must be a btrfs filesystem to be used with the btrfs snapshotter", root)
	}
	var (
		active    = filepath.Join(root, "active")
		view      = filepath.Join(root, "view")
		snapshots = filepath.Join(root, "snapshots")
	)

	for _, path := range []string{
		active,
		view,
		snapshots,
	} {
		if err := os.Mkdir(path, 0755); err != nil && !os.IsExist(err) {
			return nil, err
		}
	}
	ms, err := storage.NewMetaStore(filepath.Join(root, "metadata.db"))
	if err != nil {
		return nil, err
	}

	return &snapshotter{
		device: mnt.Source,
		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 (b *snapshotter) Stat(ctx context.Context, key string) (snapshots.Info, error) {
	ctx, t, err := b.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 (b *snapshotter) Update(ctx context.Context, info snapshots.Info, fieldpaths ...string) (snapshots.Info, error) {
	ctx, t, err := b.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 retrieves the disk usage of the top-level snapshot.
func (b *snapshotter) Usage(ctx context.Context, key string) (snapshots.Usage, error) {
	return b.usage(ctx, key)
}

func (b *snapshotter) usage(ctx context.Context, key string) (snapshots.Usage, error) {
	ctx, t, err := b.ms.TransactionContext(ctx, false)
	if err != nil {
		return snapshots.Usage{}, err
	}
	id, info, usage, err := storage.GetInfo(ctx, key)
	var parentID string
	if err == nil && info.Kind == snapshots.KindActive && info.Parent != "" {
		parentID, _, _, err = storage.GetInfo(ctx, info.Parent)

	}
	t.Rollback() // transaction no longer needed at this point.

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

	if info.Kind == snapshots.KindActive {
		var du fs.Usage
		p := filepath.Join(b.root, "active", id)
		if parentID != "" {
			du, err = fs.DiffUsage(ctx, filepath.Join(b.root, "snapshots", parentID), p)
		} else {
			du, err = fs.DiskUsage(ctx, p)
		}
		if err != nil {
			// TODO(stevvooe): Consider not reporting an error in this case.
			return snapshots.Usage{}, err
		}

		usage = snapshots.Usage(du)
	}

	return usage, nil
}

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

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

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

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

	target := filepath.Join(b.root, strings.ToLower(s.Kind.String()), s.ID)

	if len(s.ParentIDs) == 0 {
		// create new subvolume
		// btrfs subvolume create /dir
		if err = btrfs.SubvolCreate(target); err != nil {
			return nil, err
		}
	} else {
		parentp := filepath.Join(b.root, "snapshots", s.ParentIDs[0])

		var readonly bool
		if kind == snapshots.KindView {
			readonly = true
		}

		// btrfs subvolume snapshot /parent /subvol
		if err = btrfs.SubvolSnapshot(target, parentp, readonly); err != nil {
			return nil, err
		}
	}
	err = t.Commit()
	t = nil
	if err != nil {
		if derr := btrfs.SubvolDelete(target); derr != nil {
			log.G(ctx).WithError(derr).WithField("subvolume", target).Error("failed to delete subvolume")
		}
		return nil, err
	}

	return b.mounts(target, s)
}

func (b *snapshotter) mounts(dir string, s storage.Snapshot) ([]mount.Mount, error) {
	var options []string

	// get the subvolume id back out for the mount
	sid, err := btrfs.SubvolID(dir)
	if err != nil {
		return nil, err
	}

	options = append(options, fmt.Sprintf("subvolid=%d", sid))

	if s.Kind != snapshots.KindActive {
		options = append(options, "ro")
	}

	return []mount.Mount{
		{
			Type:   "btrfs",
			Source: b.device,
			// NOTE(stevvooe): While it would be nice to use to uuids for
			// mounts, they don't work reliably if the uuids are missing.
			Options: options,
		},
	}, nil
}

func (b *snapshotter) Commit(ctx context.Context, name, key string, opts ...snapshots.Opt) (err error) {
	usage, err := b.usage(ctx, key)
	if err != nil {
		return errors.Wrap(err, "failed to compute usage")
	}

	ctx, t, err := b.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.CommitActive(ctx, key, name, usage, opts...) // TODO(stevvooe): Resolve a usage value for btrfs
	if err != nil {
		return errors.Wrap(err, "failed to commit")
	}

	source := filepath.Join(b.root, "active", id)
	target := filepath.Join(b.root, "snapshots", id)

	if err := btrfs.SubvolSnapshot(target, source, true); err != nil {
		return err
	}

	err = t.Commit()
	t = nil
	if err != nil {
		if derr := btrfs.SubvolDelete(target); derr != nil {
			log.G(ctx).WithError(derr).WithField("subvolume", target).Error("failed to delete subvolume")
		}
		return err
	}

	if derr := btrfs.SubvolDelete(source); derr != nil {
		// Log as warning, only needed for cleanup, will not cause name collision
		log.G(ctx).WithError(derr).WithField("subvolume", source).Warn("failed to delete subvolume")
	}

	return nil
}

// 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 (b *snapshotter) Mounts(ctx context.Context, key string) ([]mount.Mount, error) {
	ctx, t, err := b.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 snapshot")
	}

	dir := filepath.Join(b.root, strings.ToLower(s.Kind.String()), s.ID)
	return b.mounts(dir, s)
}

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

	ctx, t, err := b.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")
			}
		}

		if removed != "" {
			if derr := btrfs.SubvolDelete(removed); derr != nil {
				log.G(ctx).WithError(derr).WithField("subvolume", removed).Warn("failed to delete subvolume")
			}
		}
	}()

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

	switch k {
	case snapshots.KindView:
		source = filepath.Join(b.root, "view", id)
		removed = filepath.Join(b.root, "view", "rm-"+id)
		readonly = true
	case snapshots.KindActive:
		source = filepath.Join(b.root, "active", id)
		removed = filepath.Join(b.root, "active", "rm-"+id)
	case snapshots.KindCommitted:
		source = filepath.Join(b.root, "snapshots", id)
		removed = filepath.Join(b.root, "snapshots", "rm-"+id)
		readonly = true
	}

	if err := btrfs.SubvolSnapshot(removed, source, readonly); err != nil {
		removed = ""
		return err
	}

	if err := btrfs.SubvolDelete(source); err != nil {
		return errors.Wrapf(err, "failed to remove snapshot %v", source)
	}

	err = t.Commit()
	t = nil
	if err != nil {
		// Attempt to restore source
		if err1 := btrfs.SubvolSnapshot(source, removed, readonly); err1 != nil {
			log.G(ctx).WithFields(logrus.Fields{
				logrus.ErrorKey: err1,
				"subvolume":     source,
				"renamed":       removed,
			}).Error("failed to restore subvolume from renamed")
			// Keep removed to allow for manual restore
			removed = ""
		}
		return err
	}

	return nil
}

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