fix trace blob detected as leaked blob in tests

Trace blob is created 3 seconds after build completion.
If this happens after test has cleaned all history records
and before it checks for leaked blobs, test can report the
trace blob as leaked. In practice it would be cleaned up
next time containerd GC gets triggered.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

control/control.go

@@ -311,6 +311,7 @@ func (c *Controller) ListenBuildHistory(req *controlapi.BuildHistoryRequest, srv
 
 func (c *Controller) UpdateBuildHistory(ctx context.Context, req *controlapi.UpdateBuildHistoryRequest) (*controlapi.UpdateBuildHistoryResponse, error) {
 	if req.Delete {
+		c.history.Finalize(ctx, req.Ref) // ignore error
 		err := c.history.Delete(ctx, req.Ref)
 		return &controlapi.UpdateBuildHistoryResponse{}, err
 	}

snapshot/containerd/content.go

@@ -115,7 +115,20 @@ func (c *nsFallbackStore) Update(ctx context.Context, info content.Info, fieldpa
 }
 
 func (c *nsFallbackStore) Walk(ctx context.Context, fn content.WalkFunc, filters ...string) error {
-	return c.main.Walk(ctx, fn, filters...)
+	seen := make(map[digest.Digest]struct{})
+	err := c.main.Walk(ctx, func(i content.Info) error {
+		seen[i.Digest] = struct{}{}
+		return fn(i)
+	}, filters...)
+	if err != nil {
+		return err
+	}
+	return c.fb.Walk(ctx, func(i content.Info) error {
+		if _, ok := seen[i.Digest]; ok {
+			return nil
+		}
+		return fn(i)
+	}, filters...)
 }
 
 func (c *nsFallbackStore) Delete(ctx context.Context, dgst digest.Digest) error {