test: add basic integration tests

Signed-off-by: Justin Chadwell <me@jedevc.com>

vendor/github.com/containerd/continuity/hardlinks.go

@@ -0,0 +1,73 @@
+/*
+   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 continuity
+
+import (
+	"fmt"
+	"os"
+)
+
+var (
+	errNotAHardLink = fmt.Errorf("invalid hardlink")
+)
+
+type hardlinkManager struct {
+	hardlinks map[hardlinkKey][]Resource
+}
+
+func newHardlinkManager() *hardlinkManager {
+	return &hardlinkManager{
+		hardlinks: map[hardlinkKey][]Resource{},
+	}
+}
+
+// Add attempts to add the resource to the hardlink manager. If the resource
+// cannot be considered as a hardlink candidate, errNotAHardLink is returned.
+func (hlm *hardlinkManager) Add(fi os.FileInfo, resource Resource) error {
+	if _, ok := resource.(Hardlinkable); !ok {
+		return errNotAHardLink
+	}
+
+	key, err := newHardlinkKey(fi)
+	if err != nil {
+		return err
+	}
+
+	hlm.hardlinks[key] = append(hlm.hardlinks[key], resource)
+
+	return nil
+}
+
+// Merge processes the current state of the hardlink manager and merges any
+// shared nodes into hard linked resources.
+func (hlm *hardlinkManager) Merge() ([]Resource, error) {
+	var resources []Resource
+	for key, linked := range hlm.hardlinks {
+		if len(linked) < 1 {
+			return nil, fmt.Errorf("no hardlink entrys for dev, inode pair: %#v", key)
+		}
+
+		merged, err := Merge(linked...)
+		if err != nil {
+			return nil, fmt.Errorf("error merging hardlink: %w", err)
+		}
+
+		resources = append(resources, merged)
+	}
+
+	return resources, nil
+}