The RH DPDK Configuration System
================================

Overview
--------

As we're aware, the DPDK configuration is an important thing to manage
well.  We have a number of concerns that must be addressed in any
configuration management system.

1. We want to make sure that we have 'conscious' configurations made up
   for each platform, and for each DPDK-enabled package
2. We want to make sure that when DPDK project adds a new configuration,
   we make a conscious decision about whether we enable that
   configuration.
3. We need to make sure that we can accommodate the wacky new
   configuration management system coming down the pipe for
   DPDK (meson+ninja).


Procedure (High level)
----------------------

Taking some inspiration from the kernel config DPDK packages will use
the following procedure:

1. We generate the DPDK configuration from source (as we do today with
   'make T=TEMPLATE config').  This creates a base configuration file.
   In this case TEMPLATE is the combination of $arch and $release that
   can vary for the package.
2. We generate a sha256 sum from that file (based on a rules engine
   described later).
3. We take a hand-built checked-in configuration (dpdk.TEMPLATE.config)
   which has a special tag inside containing the required base sha256
   sum and compare with the generated sha256 sum.
4. If the comparison succeeds, we overwrite the generated config with
   the hand-built config.  Proceed building as normal.
5. If the comparison fails, we halt the build.  Clearly a new
   configuration was introduced which was not considered and needs to be
   addressed.

It's important to note that if the default configuration changes, that
will also cause the shasum to change.  Even if the default for a
parameter that we override changes, this will trip up this simplistic
version.


SHA Sum
-------

To generate the sha256 sum:
* remove all 'comment' and empty lines
* sort the remaining lines
* calculate the sha sum

This is expressed in bash as a one-liner:

    egrep -v ^"$cmnt" $1 | egrep -v ^$ | sort -u | sha256sum | cut -d" " -f1

The new DPDK configuration will be generating into a header file
(rte_config.h), and so some 'forward' consideration was given to making
the comment line as configurable (instead of using straight '#') - hence the
'$cmnt' variable.

The SHA sum will be identified in the 'new' header by the standard ascii
tag format:

# -*- cfg-sha: [a-z0-9]+

Or in the case of a .c file:
/* -*- cfg-sha: [a-z0-9]+ */


Helper scripts
--------------

Included are a set of scripts for DPDK configuration, which replaces
the original setconf functions in the old spec file.

* set_config.sh - A script which copies the new DPDK configuration over the
                  old one.  This validates the sha sum.
* gen_config_group.sh - A script which reads the .spec file for all of the
                        architectures and generates starting configurations.
                        Use this script to get a baseline configuration for
                        modifying.
* configlib.sh - A library for generating and reading SHA sums.