Move labels to pkg/labels

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

pkg/labels/labels.go

@@ -0,0 +1,29 @@
+/*
+   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 labels
+
+// LabelUncompressed is added to compressed layer contents.
+// The value is digest of the uncompressed content.
+const LabelUncompressed = "containerd.io/uncompressed"
+
+// LabelSharedNamespace is added to a namespace to allow that namespaces
+// contents to be shared.
+const LabelSharedNamespace = "containerd.io/namespace.shareable"
+
+// LabelDistributionSource is added to content to indicate its origin.
+// e.g., "containerd.io/distribution.source.docker.io=library/redis"
+const LabelDistributionSource = "containerd.io/distribution.source"