How to target database connection file once in PHP?
===

My PHP application has different config files with their different settings and their different paths. But all of them need to access to just one database connection file. I would like to avoid mention its path separately on them with many `../` and `../../`. How can I write a same code and use it in all of them?  
Imagine that my PHP application has this hierarchy for its config files:  

> root  
  root/config/db.php  (This file is what I want to mention from all config files.)  
  root/admin/config/conf.php  
  root/users/conf.php 

Actually what I need is something that detect the root path of my project and create a same directory path generally.