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overlay.go
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overlay.go
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// +build linux
package overlay
import (
"context"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"strings"
"syscall"
"github.com/containerd/containerd/fs"
"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/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("Failure rolling back 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("Failure rolling back 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
}
s, err := storage.CreateSnapshot(ctx, kind, key, parent, opts...)
if err != nil {
if rerr := t.Rollback(); rerr != nil {
log.G(ctx).WithError(rerr).Warn("Failure rolling back transaction")
}
return nil, errors.Wrap(err, "failed to create active")
}
if len(s.ParentIDs) > 0 {
st, err := os.Stat(filepath.Join(o.upperPath(s.ParentIDs[0])))
if err != nil {
if rerr := t.Rollback(); rerr != nil {
log.G(ctx).WithError(rerr).Warn("Failure rolling back transaction")
}
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 {
if rerr := t.Rollback(); rerr != nil {
log.G(ctx).WithError(rerr).Warn("Failure rolling back transaction")
}
return nil, errors.Wrap(err, "failed to chown")
}
}
path = filepath.Join(snapshotDir, s.ID)
if err = os.Rename(td, path); err != nil {
if rerr := t.Rollback(); rerr != nil {
log.G(ctx).WithError(rerr).Warn("Failure rolling back transaction")
}
return nil, errors.Wrap(err, "failed to rename")
}
td = ""
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()
}