Allow opts to flow to the backend snapshotter during snapshot creation.

Signed-off-by: Eric Hotinger <ehotinger@gmail.com>

metadata/snapshot.go

@@ -34,6 +34,10 @@ import (
 	bolt "go.etcd.io/bbolt"
 )
 
+const (
+	inheritedLabelsPrefix = "containerd.io/snapshot/"
+)
+
 type snapshotter struct {
 	snapshots.Snapshotter
 	name string
@@ -338,12 +342,14 @@ func (s *snapshotter) createSnapshot(ctx context.Context, key, parent string, re
 			return err
 		}
 
+		inheritedOpt := snapshots.WithLabels(filterInheritedLabels(base.Labels))
+
 		// TODO: Consider doing this outside of transaction to lessen
 		// metadata lock time
 		if readonly {
-			m, err = s.Snapshotter.View(ctx, bkey, bparent)
+			m, err = s.Snapshotter.View(ctx, bkey, bparent, inheritedOpt)
 		} else {
-			m, err = s.Snapshotter.Prepare(ctx, bkey, bparent)
+			m, err = s.Snapshotter.Prepare(ctx, bkey, bparent, inheritedOpt)
 		}
 		return err
 	}); err != nil {
@@ -445,9 +451,11 @@ func (s *snapshotter) Commit(ctx context.Context, name, key string, opts ...snap
 			return err
 		}
 
+		inheritedOpt := snapshots.WithLabels(filterInheritedLabels(base.Labels))
+
 		// TODO: Consider doing this outside of transaction to lessen
 		// metadata lock time
-		return s.Snapshotter.Commit(ctx, nameKey, bkey)
+		return s.Snapshotter.Commit(ctx, nameKey, bkey, inheritedOpt)
 	})
 
 }
@@ -761,3 +769,19 @@ func (s *snapshotter) pruneBranch(ctx context.Context, node *treeNode) error {
 func (s *snapshotter) Close() error {
 	return s.Snapshotter.Close()
 }
+
+// filterInheritedLabels filters the provided labels by removing any key which doesn't have
+// a prefix of "containerd.io/snapshot/".
+func filterInheritedLabels(labels map[string]string) map[string]string {
+	if labels == nil {
+		return nil
+	}
+
+	filtered := make(map[string]string)
+	for k, v := range labels {
+		if strings.HasPrefix(k, inheritedLabelsPrefix) {
+			filtered[k] = v
+		}
+	}
+	return filtered
+}

metadata/snapshot_test.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"os"
 	"path/filepath"
+	"reflect"
 	"runtime"
 	"testing"
 
@@ -63,3 +64,41 @@ func TestMetadata(t *testing.T) {
 	testutil.RequiresRoot(t)
 	testsuite.SnapshotterSuite(t, "Metadata", newTestSnapshotter)
 }
+
+func TestFilterInheritedLabels(t *testing.T) {
+	tests := []struct {
+		labels   map[string]string
+		expected map[string]string
+	}{
+		{
+			nil,
+			nil,
+		},
+		{
+			map[string]string{},
+			map[string]string{},
+		},
+		{
+			map[string]string{"": ""},
+			map[string]string{},
+		},
+		{
+			map[string]string{"foo": "bar"},
+			map[string]string{},
+		},
+		{
+			map[string]string{inheritedLabelsPrefix + "foo": "bar"},
+			map[string]string{inheritedLabelsPrefix + "foo": "bar"},
+		},
+		{
+			map[string]string{inheritedLabelsPrefix + "foo": "bar", "qux": "qaz"},
+			map[string]string{inheritedLabelsPrefix + "foo": "bar"},
+		},
+	}
+
+	for _, test := range tests {
+		if actual := filterInheritedLabels(test.labels); !reflect.DeepEqual(actual, test.expected) {
+			t.Fatalf("expected %v but got %v", test.expected, actual)
+		}
+	}
+}

snapshots/snapshotter.go

@@ -86,10 +86,15 @@ func (k *Kind) UnmarshalJSON(b []byte) error {
 // Info provides information about a particular snapshot.
 // JSON marshallability is supported for interactive with tools like ctr,
 type Info struct {
-	Kind    Kind              // active or committed snapshot
-	Name    string            // name or key of snapshot
-	Parent  string            `json:",omitempty"` // name of parent snapshot
-	Labels  map[string]string `json:",omitempty"` // Labels for snapshot
+	Kind   Kind   // active or committed snapshot
+	Name   string // name or key of snapshot
+	Parent string `json:",omitempty"` // name of parent snapshot
+
+	// Labels for a snapshot.
+	//
+	// Note: only labels prefixed with `containerd.io/snapshot/` will be inherited by the
+	// snapshotter's `Prepare`, `View`, or `Commit` calls.
+	Labels  map[string]string `json:",omitempty"`
 	Created time.Time         `json:",omitempty"` // Created time
 	Updated time.Time         `json:",omitempty"` // Last update time
 }