func (o *snapshotter) mounts(s storage.Snapshot, info snapshots.Info) []mount.Mount {
	var options []string
…
	if len(s.ParentIDs) == 0 {
		// if we only have one layer/no parents then just return a bind mount as overlay
		// will not work
		roFlag := "rw"
		if s.Kind == snapshots.KindView {
			roFlag = "ro"
		}
		return []mount.Mount{
			{
				Source: o.upperPath(s.ID),
				Type:   "bind",
				Options: append(options,
					roFlag,
					"rbind",
				),
			},
		}
	}

	if s.Kind == snapshots.KindActive {
		options = append(options,
			"workdir="+o.workPath(s.ID),
			"upperdir="+o.upperPath(s.ID),
		)
	} else if len(s.ParentIDs) == 1 {
		return []mount.Mount{
			{
				Source: o.upperPath(s.ParentIDs[0]),
				Type:   "bind",
				Options: append(options,
					"ro",
					"rbind",
				),
			},
		}
	}

	parentPaths := make([]string, len(s.ParentIDs))
	for i := range s.ParentIDs {
		parentPaths[i] = o.upperPath(s.ParentIDs[i])
	}
	options = append(options, "lowerdir="+strings.Join(parentPaths, ":"))
	options = append(options, o.options...)

	return []mount.Mount{
		{
			Type:    "overlay",
			Source:  "overlay",
			Options: options,
		},
	}
}

Warm-up