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btrfs.go
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btrfs.go
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// +build linux
package btrfs
import (
"context"
"fmt"
"os"
"path/filepath"
"github.com/Sirupsen/logrus"
"github.com/containerd/btrfs"
"github.com/containerd/containerd/log"
"github.com/containerd/containerd/mount"
"github.com/containerd/containerd/plugin"
"github.com/containerd/containerd/snapshot"
"github.com/containerd/containerd/snapshot/storage"
"github.com/pkg/errors"
)
func init() {
plugin.Register(&plugin.Registration{
ID: "btrfs",
Type: plugin.SnapshotPlugin,
Init: func(ic *plugin.InitContext) (interface{}, error) {
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) (snapshot.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")
snapshots = filepath.Join(root, "snapshots")
)
for _, path := range []string{
active,
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) (snapshot.Info, error) {
ctx, t, err := b.ms.TransactionContext(ctx, false)
if err != nil {
return snapshot.Info{}, err
}
defer t.Rollback()
_, info, _, err := storage.GetInfo(ctx, key)
if err != nil {
return snapshot.Info{}, err
}
return info, nil
}
// Usage retrieves the disk usage of the top-level snapshot.
func (b *snapshotter) Usage(ctx context.Context, key string) (snapshot.Usage, error) {
panic("not implemented")
// TODO(stevvooe): Btrfs has a quota model where data can be exclusive to a
// snapshot or shared among other resources. We may find that this is the
// correct value to reoprt but the stability of the implementation is under
// question.
//
// In general, this has impact on the model we choose for reporting usage.
// Ideally, the value should allow aggregration. For overlay, this is
// simple since we can scan the diff directory to get a unique value. This
// breaks down when start looking the behavior when data is shared between
// snapshots, such as that for btrfs.
}
// Walk the committed snapshots.
func (b *snapshotter) Walk(ctx context.Context, fn func(context.Context, snapshot.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) ([]mount.Mount, error) {
return b.makeActive(ctx, key, parent, false)
}
func (b *snapshotter) View(ctx context.Context, key, parent string) ([]mount.Mount, error) {
return b.makeActive(ctx, key, parent, true)
}
func (b *snapshotter) makeActive(ctx context.Context, key, parent string, readonly bool) ([]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("Failure rolling back transaction")
}
}
}()
a, err := storage.CreateActive(ctx, key, parent, readonly)
if err != nil {
return nil, err
}
target := filepath.Join(b.root, "active", a.ID)
if len(a.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", a.ParentIDs[0])
// btrfs subvolume snapshot /parent /subvol
if err = btrfs.SubvolSnapshot(target, parentp, a.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)
}
func (b *snapshotter) mounts(dir string) ([]mount.Mount, error) {
var options []string
// get the subvolume id back out for the mount
info, err := btrfs.SubvolInfo(dir)
if err != nil {
return nil, err
}
options = append(options, fmt.Sprintf("subvolid=%d", info.ID))
if info.Readonly {
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) (err error) {
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("Failure rolling back transaction")
}
}
}()
id, err := storage.CommitActive(ctx, key, name, snapshot.Usage{}) // 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
}
a, err := storage.GetActive(ctx, key)
t.Rollback()
if err != nil {
return nil, errors.Wrap(err, "failed to get active snapshot")
}
dir := filepath.Join(b.root, "active", a.ID)
return b.mounts(dir)
}
// 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("Failure rolling back 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")
}
if k == snapshot.KindActive {
source = filepath.Join(b.root, "active", id)
info, err := btrfs.SubvolInfo(source)
if err != nil {
source = ""
return err
}
readonly = info.Readonly
removed = filepath.Join(b.root, "active", "rm-"+id)
} else {
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
}