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Add blockfile snapshotter
Signed-off-by: Derek McGowan <[email protected]>
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‎snapshots/blockfile/blockfile.go‎

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/*
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Copyright The containerd Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package blockfile
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import (
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"context"
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"fmt"
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"os"
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"path/filepath"
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"github.com/containerd/containerd/log"
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"github.com/containerd/containerd/mount"
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"github.com/containerd/containerd/plugin"
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"github.com/containerd/containerd/snapshots"
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"github.com/containerd/containerd/snapshots/storage"
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"github.com/containerd/continuity/fs"
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)
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// SnapshotterConfig holds the configurable properties for the blockfile snapshotter
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type SnapshotterConfig struct {
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// recreateScratch is whether scratch should be recreated even
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// if already exists
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recreateScratch bool
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scratchGenerator func(string) error
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// fsType is the filesystem type for the mount (defaults to ext4)
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fsType string
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}
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// Opt is an option to configure the overlay snapshotter
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type Opt func(string, *SnapshotterConfig)
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// WithScratchFile provides a scratch file which will get copied on startup
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// if the scratch file needs to be generated.
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func WithScratchFile(src string) Opt {
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return func(root string, config *SnapshotterConfig) {
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config.scratchGenerator = func(dst string) error {
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// Copy src to dst
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scratch := filepath.Join(root, "scratch")
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if err := fs.CopyFile(scratch, src); err != nil {
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return fmt.Errorf("failed to copy scratch: %w", err)
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}
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return nil
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}
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}
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}
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// WithFSType defines the filesystem type to apply to mounts of the blockfile
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func WithFSType(fsType string) Opt {
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return func(root string, config *SnapshotterConfig) {
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config.fsType = fsType
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}
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}
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type snapshotter struct {
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root string
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scratch string
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fsType string
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ms *storage.MetaStore
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}
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// NewSnapshotter returns a Snapshotter which copies layers on the underlying
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// file system. A metadata file is stored under the root.
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func NewSnapshotter(root string, opts ...Opt) (snapshots.Snapshotter, error) {
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var config SnapshotterConfig
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if err := os.MkdirAll(root, 0700); err != nil {
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return nil, err
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}
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for _, opt := range opts {
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opt(root, &config)
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}
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scratch := filepath.Join(root, "scratch")
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createScratch := config.recreateScratch
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if !createScratch {
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if _, err := os.Stat(scratch); err != nil {
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if !os.IsNotExist(err) {
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return nil, fmt.Errorf("unable to stat scratch file: %w", err)
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}
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createScratch = true
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}
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}
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if createScratch {
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if config.scratchGenerator == nil {
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return nil, fmt.Errorf("no scratch file generator: %w", plugin.ErrSkipPlugin)
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}
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if err := config.scratchGenerator(scratch); err != nil {
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return nil, fmt.Errorf("failed to generate scratch file: %w", err)
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}
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}
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if config.fsType == "" {
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config.fsType = "ext4"
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}
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ms, err := storage.NewMetaStore(filepath.Join(root, "metadata.db"))
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if err != nil {
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return nil, err
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}
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if err := os.Mkdir(filepath.Join(root, "snapshots"), 0700); err != nil && !os.IsExist(err) {
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return nil, err
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}
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return &snapshotter{
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root: root,
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scratch: scratch,
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fsType: config.fsType,
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ms: ms,
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}, nil
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}
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// Stat returns the info for an active or committed snapshot by name or
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// key.
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//
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// Should be used for parent resolution, existence checks and to discern
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// the kind of snapshot.
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func (o *snapshotter) Stat(ctx context.Context, key string) (info snapshots.Info, err error) {
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err = o.ms.WithTransaction(ctx, false, func(ctx context.Context) error {
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_, info, _, err = storage.GetInfo(ctx, key)
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return err
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})
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if err != nil {
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return snapshots.Info{}, err
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}
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return info, nil
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}
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func (o *snapshotter) Update(ctx context.Context, info snapshots.Info, fieldpaths ...string) (_ snapshots.Info, err error) {
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err = o.ms.WithTransaction(ctx, true, func(ctx context.Context) error {
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info, err = storage.UpdateInfo(ctx, info, fieldpaths...)
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return err
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})
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if err != nil {
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return snapshots.Info{}, err
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}
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return info, nil
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}
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func (o *snapshotter) Usage(ctx context.Context, key string) (usage snapshots.Usage, err error) {
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var (
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id string
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info snapshots.Info
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)
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err = o.ms.WithTransaction(ctx, false, func(ctx context.Context) error {
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id, info, usage, err = storage.GetInfo(ctx, key)
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if err != nil {
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return err
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}
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// Current usage calculation is an approximation based on the size
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// of the block file - the size of its parent. This does not consider
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// that the filesystem may not support shared extents between the block
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// file and its parents, in which case the accurate calculation would just
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// be the size of the block file. Additionally, this does not take into
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// consideration that file may have been removed before being adding,
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// making the number of shared extents between the parent and the block
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// file smaller than the parent, under reporting actual usage.
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//
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// A more ideal calculation would look like:
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// size(block) - usage(extent_intersection(block,parent))
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// OR
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// usage(extent_union(block,parent)) - size(parent)
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if info.Kind == snapshots.KindActive {
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// TODO: Use size calculator from fs package
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st, err := os.Stat(o.getBlockFile(id))
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if err != nil {
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return err
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}
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usage.Size = st.Size()
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usage.Inodes = 1
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}
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if info.Parent != "" {
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// GetInfo returns total number of bytes used by a snapshot (including parent).
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// So subtract parent usage in order to get delta consumed by layer itself.
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_, _, parentUsage, err := storage.GetInfo(ctx, info.Parent)
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if err != nil {
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return err
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}
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usage.Size -= parentUsage.Size
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}
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return err
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})
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if err != nil {
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return snapshots.Usage{}, err
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}
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return usage, nil
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}
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func (o *snapshotter) Prepare(ctx context.Context, key, parent string, opts ...snapshots.Opt) ([]mount.Mount, error) {
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return o.createSnapshot(ctx, snapshots.KindActive, key, parent, opts)
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}
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func (o *snapshotter) View(ctx context.Context, key, parent string, opts ...snapshots.Opt) ([]mount.Mount, error) {
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return o.createSnapshot(ctx, snapshots.KindView, key, parent, opts)
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}
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// Mounts returns the mounts for the transaction identified by key. Can be
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// called on an read-write or readonly transaction.
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//
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// This can be used to recover mounts after calling View or Prepare.
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func (o *snapshotter) Mounts(ctx context.Context, key string) (_ []mount.Mount, err error) {
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var s storage.Snapshot
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err = o.ms.WithTransaction(ctx, false, func(ctx context.Context) error {
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s, err = storage.GetSnapshot(ctx, key)
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if err != nil {
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return fmt.Errorf("failed to get snapshot mount: %w", err)
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}
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return nil
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})
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if err != nil {
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return nil, err
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}
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return o.mounts(s), nil
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}
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func (o *snapshotter) Commit(ctx context.Context, name, key string, opts ...snapshots.Opt) error {
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return o.ms.WithTransaction(ctx, true, func(ctx context.Context) error {
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id, _, _, err := storage.GetInfo(ctx, key)
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if err != nil {
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return err
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}
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st, err := os.Stat(o.getBlockFile(id))
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if err != nil {
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return err
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}
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usage := snapshots.Usage{
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Size: st.Size(),
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Inodes: 1,
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}
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if _, err = storage.CommitActive(ctx, key, name, usage, opts...); err != nil {
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return fmt.Errorf("failed to commit snapshot: %w", err)
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}
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return nil
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})
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}
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// Remove abandons the transaction identified by key. All resources
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// associated with the key will be removed.
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func (o *snapshotter) Remove(ctx context.Context, key string) (err error) {
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var (
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renamed, path string
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restore bool
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)
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err = o.ms.WithTransaction(ctx, true, func(ctx context.Context) error {
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id, _, err := storage.Remove(ctx, key)
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if err != nil {
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return fmt.Errorf("failed to remove: %w", err)
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}
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path = o.getBlockFile(id)
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renamed = filepath.Join(o.root, "snapshots", "rm-"+id)
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if err = os.Rename(path, renamed); err != nil {
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if !os.IsNotExist(err) {
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return fmt.Errorf("failed to rename: %w", err)
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}
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renamed = ""
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}
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restore = true
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return nil
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})
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if err != nil {
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if renamed != "" && restore {
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if err1 := os.Rename(renamed, path); err1 != nil {
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// May cause inconsistent data on disk
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log.G(ctx).WithError(err1).WithField("path", renamed).Error("failed to rename after failed commit")
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}
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}
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return err
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}
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if renamed != "" {
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if err := os.Remove(renamed); err != nil {
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// Must be cleaned up, any "rm-*" could be removed if no active transactions
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log.G(ctx).WithError(err).WithField("path", renamed).Warnf("failed to remove root filesystem")
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}
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}
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return nil
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}
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// Walk the committed snapshots.
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func (o *snapshotter) Walk(ctx context.Context, fn snapshots.WalkFunc, fs ...string) error {
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return o.ms.WithTransaction(ctx, false, func(ctx context.Context) error {
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return storage.WalkInfo(ctx, fn, fs...)
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})
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}
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func (o *snapshotter) createSnapshot(ctx context.Context, kind snapshots.Kind, key, parent string, opts []snapshots.Opt) (_ []mount.Mount, err error) {
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var s storage.Snapshot
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err = o.ms.WithTransaction(ctx, true, func(ctx context.Context) error {
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s, err = storage.CreateSnapshot(ctx, kind, key, parent, opts...)
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if err != nil {
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return fmt.Errorf("failed to create snapshot: %w", err)
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}
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if len(s.ParentIDs) == 0 || s.Kind == snapshots.KindActive {
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path := o.getBlockFile(s.ID)
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if len(s.ParentIDs) > 0 {
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if err = fs.CopyFile(path, o.getBlockFile(s.ParentIDs[0])); err != nil {
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return fmt.Errorf("copying of parent failed: %w", err)
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}
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} else {
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if err = fs.CopyFile(path, o.scratch); err != nil {
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return fmt.Errorf("copying of scratch failed: %w", err)
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}
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}
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}
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return nil
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})
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if err != nil {
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return nil, err
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}
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return o.mounts(s), nil
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}
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func (o *snapshotter) getBlockFile(id string) string {
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return filepath.Join(o.root, "snapshots", id)
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}
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func (o *snapshotter) mounts(s storage.Snapshot) []mount.Mount {
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var (
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mountOptions = []string{
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"loop",
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}
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source string
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)
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if s.Kind == snapshots.KindView {
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mountOptions = append(mountOptions, "ro")
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} else {
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mountOptions = append(mountOptions, "rw")
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}
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if len(s.ParentIDs) == 0 || s.Kind == snapshots.KindActive {
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source = o.getBlockFile(s.ID)
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} else {
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source = o.getBlockFile(s.ParentIDs[0])
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}
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return []mount.Mount{
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{
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Source: source,
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Type: o.fsType,
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Options: mountOptions,
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},
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}
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}
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// Close closes the snapshotter
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func (o *snapshotter) Close() error {
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return o.ms.Close()
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}

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