Description of problem:

The vdo script's config file parsing is overly restrictive in that adding any new
fields will cause old versions of the script to reject the entire file. In any scenario which involves making VDO devices on RHEL7.5, upgrading the OS to a later version, and then later moving back to RHEL7.5 can encounter a problem.
These issues can occur in one of two ways:

Modifying the configuring of an existing volume with a newer vdo script, or creating new volumes with the newer script. Although we don't expect the old script to be able to manage newer volumes, this would also prevent managing the older volumes.


Version-Release number of selected component (if applicable):

vdo-6.1.1.111


How reproducible:

Currently, there is no way to induce this problem. Once there is a change to the set of parameters in the vdo config file, this is 100% reproducable.

Steps to Reproduce:
1. Make a VDO volume on RHEL7.5
2. Move the volume and config file to a RHEL7.6 host (or upgrade the existing host).
3. Create a new VDO volume
4. Move the volume and config file back to a RHEL7.5 host (or downgrade the existing host).
5. Attempt to start the old volume.

Actual results:

vdo script fails to read the config file

Expected results:

vdo script correctly starts the old volume

Additional info: