// sameMount reports whether childInfo and parentInfo describe
// the same file or directory in the same mount. For example,
// on Unix this means that the device fields of the two underlying
// structures are identical; on other systems the decision may
// be based on the path names. sameMount only applies to results
// returned by os.Stat. It returns false in other cases.
func sameMount(childInfo os.FileInfo, childPath string, parentInfo os.FileInfo, parentPath string) bool {
       if childInfo == nil || parentInfo == nil {
               return false
       }
       if childPath == "" || parentPath == "" {
               return false
       }
       fi1, ok1 := childInfo.Sys().(*syscall.Stat_t)
       fi2, ok2 := parentInfo.Sys().(*syscall.Stat_t)
       if !ok1 || !ok2 {
               return false
       }
       return fi1.Dev == fi2.Dev
}