You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: image_unix.go
    path of file: ./repos/moby/daemon/images
    
    the code of the file until where you have to start completion: //go:build linux || freebsd

package images // import "github.com/docker/docker/daemon/images"

import (
	"context"

	"github.com/containerd/log
    
func (i *ImageService) GetContainerLayerSize(ctx context.Context, containerID string) (int64, int64, error) {
	var (
		sizeRw, sizeRootfs int64
		err                error
	)

	// Safe to index by runtime.GOOS as Unix hosts don't support multiple
	// container operating systems.
	rwlayer, err := i.layerStore.GetRWLayer(containerID)
	if err != nil {
		log.G(ctx).Errorf("Failed to compute size of container rootfs %v: %v", containerID, err)
		return sizeRw, sizeRootfs, nil
	}
	defer i.layerStore.ReleaseRWLayer(rwlayer)

	sizeRw, err = rwlayer.Size()
	if err != nil {
		log.G(ctx).Errorf("Driver %s couldn't return diff size of container %s: %s",
			i.layerStore.DriverName(), containerID, err)
		// FIXME: GetSize should return an error. Not changing it now in case
		// there is a side-effect.
		sizeRw = -1
	}

	if parent := rwlayer.Parent(); parent != nil {
		sizeRootfs = parent.Size()
		if sizeRw != -1 {
			sizeRootfs += sizeRw
		}
	}
	return sizeRw, sizeRootfs, nil
}