Implement btrfs usage

Implements btrfs usage using a double walking diff and
counting the result. Walking gives the most accurate
count and includes inode usage.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

fs/du.go

@@ -1,5 +1,7 @@
 package fs
 
+import "context"
+
 // Usage of disk information
 type Usage struct {
 	Inodes int64
@@ -11,3 +13,10 @@ type Usage struct {
 func DiskUsage(roots ...string) (Usage, error) {
 	return diskUsage(roots...)
 }
+
+// DiffUsage counts the numbers of inodes and disk usage in the
+// diff between the 2 directories. The first path is intended
+// as the base directory and the second as the changed directory.
+func DiffUsage(ctx context.Context, a, b string) (Usage, error) {
+	return diffUsage(ctx, a, b)
+}

fs/du_unix.go

@@ -3,17 +3,19 @@
 package fs
 
 import (
+	"context"
 	"os"
 	"path/filepath"
 	"syscall"
 )
 
-func diskUsage(roots ...string) (Usage, error) {
-	type inode struct {
+type inode struct {
 	// TODO(stevvooe): Can probably reduce memory usage by not tracking
 	// device, but we can leave this right for now.
 	dev, ino uint64
-	}
+}
+
+func diskUsage(roots ...string) (Usage, error) {
 
 	var (
 		size   int64
@@ -45,3 +47,37 @@ func diskUsage(roots ...string) (Usage, error) {
 		Size:   size,
 	}, nil
 }
+
+func diffUsage(ctx context.Context, a, b string) (Usage, error) {
+	var (
+		size   int64
+		inodes = map[inode]struct{}{} // expensive!
+	)
+
+	if err := Changes(ctx, a, b, func(kind ChangeKind, _ string, fi os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if kind == ChangeKindAdd || kind == ChangeKindModify {
+			stat := fi.Sys().(*syscall.Stat_t)
+
+			inoKey := inode{dev: uint64(stat.Dev), ino: uint64(stat.Ino)}
+			if _, ok := inodes[inoKey]; !ok {
+				inodes[inoKey] = struct{}{}
+				size += fi.Size()
+			}
+
+			return nil
+
+		}
+		return nil
+	}); err != nil {
+		return Usage{}, err
+	}
+
+	return Usage{
+		Inodes: int64(len(inodes)),
+		Size:   size,
+	}, nil
+}

fs/du_windows.go

@@ -3,6 +3,7 @@
 package fs
 
 import (
+	"context"
 	"os"
 	"path/filepath"
 )
@@ -31,3 +32,29 @@ func diskUsage(roots ...string) (Usage, error) {
 		Size: size,
 	}, nil
 }
+
+func diffUsage(ctx context.Context, a, b string) (Usage, error) {
+	var (
+		size int64
+	)
+
+	if err := Changes(ctx, a, b, func(kind ChangeKind, _ string, fi os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if kind == ChangeKindAdd || kind == ChangeKindModify {
+			size += fi.Size()
+
+			return nil
+
+		}
+		return nil
+	}); err != nil {
+		return Usage{}, err
+	}
+
+	return Usage{
+		Size: size,
+	}, nil
+}

snapshots/btrfs/btrfs.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 
 	"github.com/containerd/btrfs"
+	"github.com/containerd/containerd/fs"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/mount"
 	"github.com/containerd/containerd/platforms"
@@ -128,18 +129,43 @@ func (b *snapshotter) Update(ctx context.Context, info snapshots.Info, fieldpath
 
 // Usage retrieves the disk usage of the top-level snapshot.
 func (b *snapshotter) Usage(ctx context.Context, key string) (snapshots.Usage, error) {
-	panic("not implemented")
+	return b.usage(ctx, key)
+}
 
-	// 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.
+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(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.
@@ -238,6 +264,11 @@ func (b *snapshotter) mounts(dir string, s storage.Snapshot) ([]mount.Mount, err
 }
 
 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
@@ -250,7 +281,7 @@ func (b *snapshotter) Commit(ctx context.Context, name, key string, opts ...snap
 		}
 	}()
 
-	id, err := storage.CommitActive(ctx, key, name, snapshots.Usage{}, opts...) // TODO(stevvooe): Resolve a usage value for btrfs
+	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")
 	}