title: How to keep config after reinstall ipk on OpenWrt
body: <p>In makefile, I use <code>INSTALL_DATA</code> to copy config file to <code>/etc/config</code>. And config file will be changed during running.</p>
  
  <p>I found that, after re-install application, the config file will restore to default one packed in ipk.</p>
  
  <p>I want to know how to keep config file after re-install. Anyone can help me?</p>
  
  <p>Makefile:</p>
  
  <pre><code>define Package/zm_control/install
      $(INSTALL_DIR) $(1)/etc/config
      $(INSTALL_DATA) ./config/$(PKG_NAME).json $(1)/etc/config/$(PKG_NAME).json
  endef
  </code></pre>