IMPORTANT NOTE:
***********************************************************************
hooks are NOT part of VDSM. They are extensions that -
if found useful - are to be integrated into oVirt in
general and into VDSM in particular.
Do not rely on their existence here.
***********************************************************************

Working with VDSM hooks
=======================
To work with VDSM hooks you need first to do the following:
1. Update UserDefinedVMProperties property by using the engine-config tool:
   # engine-config -s UserDefinedVMProperties='pincpu=^[0-9]+$' --cver=3.0
   * Note: for simplification we use pincpu=^[0-9]+$ which enable only numbers, the actual
           regex need to be pincpu=^[\^]?\d+(-\d+)?(,[\^]?\d+(-\d+)?)*$ which enable range of CPUs.

   That command will enable VMs to use pincpu custom hook.
   * Please note that this command will override the existing value of UserDefinedVMProperties
     you can concatenate the old value by getting it with the following command:
     # engine-config -g UserDefinedVMProperties --cver=3.0
   * note for the version in engine-config tool, the current version is 3.0 and its the first
     version that use custom hooks, to use the version you can do the following:
     # engine-config -g UserDefinedVMProperties --cver=3.0

   If you want to enable more then one custom hook use the semicolon as
   a separator:
   # engine-config -s UserDefinedVMProperties='pincpu=^[0-9]+$;sap_agent=^(true|false)$' --cver=3.0

   The convention is [hook name]=[value], the value is evaluate with regular expression,
   If you find regular expression too complex, you can always use the following command:
   # engine-config -s UserDefinedVMProperties='pincpu=.*' --cver=3.0

   Which mean that oVirt-engine validation will get any input - but please note that giving
   a bad input - the hook will probably fail or run with unexpected results!

   There is explanation to each hooks expected syntax in the syntax section in this
   README file.

2. In order that your changes will take effect you need to restart the JBoss service:
   # service jbossas restart

3. Edit the VM that you want to run the hook with by running the oVirt-engine Admin GUI and
   do one of the following options:
   a. Select the VM and press "edit" button - edit dialog will pop-up,
      select the last option from the left option list with the label "Custom Properties"
      add your custom property value, in our pincpu hook case:
      pincpu=1
      if you want to use more then on hook and you did enable it with the engine-config
      tool, you can use the semicolon as a separator:
      pincpu=1;sap_agent=true
   b. Another option is to use "Run Once" dialog which mean that you add a custom property
      only this time to the VM, next time that you run the VM it will run without the
      custom property that you provided.
      The "Run Once" dialog can be found in the VMs tab at the drop down menu beside the
      green "Play" button (after the "Remove" button).
      At the "Run Once" dialog in the lower panel you will see a label with
      "Custom Properties" and an input box that you can use as explain in the "edit" dialog
      option.