Move rootfs to pkg/rootfs

Signed-off-by: Derek McGowan <derek@mcg.dev>

pkg/rootfs/diff.go

@@ -0,0 +1,67 @@
+/*
+   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 rootfs
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/containerd/containerd/v2/core/diff"
+	"github.com/containerd/containerd/v2/core/mount"
+	"github.com/containerd/containerd/v2/core/snapshots"
+	"github.com/containerd/containerd/v2/pkg/cleanup"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+)
+
+// CreateDiff creates a layer diff for the given snapshot identifier from the
+// parent of the snapshot. A content ref is provided to track the progress of
+// the content creation and the provided snapshotter and mount differ are used
+// for calculating the diff. The descriptor for the layer diff is returned.
+func CreateDiff(ctx context.Context, snapshotID string, sn snapshots.Snapshotter, d diff.Comparer, opts ...diff.Opt) (ocispec.Descriptor, error) {
+	info, err := sn.Stat(ctx, snapshotID)
+	if err != nil {
+		return ocispec.Descriptor{}, err
+	}
+
+	lowerKey := fmt.Sprintf("%s-parent-view-%s", info.Parent, uniquePart())
+	lower, err := sn.View(ctx, lowerKey, info.Parent)
+	if err != nil {
+		return ocispec.Descriptor{}, err
+	}
+	defer cleanup.Do(ctx, func(ctx context.Context) {
+		sn.Remove(ctx, lowerKey)
+	})
+
+	var upper []mount.Mount
+	if info.Kind == snapshots.KindActive {
+		upper, err = sn.Mounts(ctx, snapshotID)
+		if err != nil {
+			return ocispec.Descriptor{}, err
+		}
+	} else {
+		upperKey := fmt.Sprintf("%s-view-%s", snapshotID, uniquePart())
+		upper, err = sn.View(ctx, upperKey, snapshotID)
+		if err != nil {
+			return ocispec.Descriptor{}, err
+		}
+		defer cleanup.Do(ctx, func(ctx context.Context) {
+			sn.Remove(ctx, upperKey)
+		})
+	}
+
+	return d.Compare(ctx, lower, upper, opts...)
+}