[elrepo] How to understand elrepo kernel config changes

[Phil Perry]

On 02/08/2019 07:58, Chengwei Yang wrote:
> Hi there,
> 
> I'm new to elrepo and I found that the goal of elrepo is exactly the same as me.
> 
> I checked kernel-lt and found that it brings a config file which I curious a lot
> how to understand what it does, because I found there are a lot of changes from
> centos 3.10.0 kernel config.
> 
> I did below to check config changes:
> 
> ```
> [root at linux-4.4.186]# cp /boot/config-3.10.0-693.21.1.el7.x86_64 .config
> [root at linux-4.4.186]# make -s ARCH=x86_64 listnewconfig | wc -l
> .config:3082:warning: symbol value 'm' invalid for PINCTRL_AMD
> 506
> ```
> 
> so there are 506 new changes.
> 
> I make all new changes as default configs.
> 
> ```
> [root at linux-4.4.186]# make -s ARCH=x86_64 alldefconfig
> [root at linux-4.4.186]# make -s ARCH=x86_64 listnewconfig |wc -l
> 0
> ```
> 
> and then check the diff.
> 
> ```
> [root at linux-4.4.186]# diff -u .config config-4.4.186-x86_64 |wc -l
> 7712
> ```
> 
> There are a lot of changes from default configs, please help me to understand
> what config-4.4.186-x86_64 changes.
> 

I guess I should explain the history of how we ended up where we are 
today with the config file.

The config file started it's life around the time of kernel-3.14. The 
current RHEL el7 kernel config was taken as a starting point and all new 
options were reviewed and set on a case by case basis to generate an 
initial release candidate. A lot of testing and further release 
candidates followed and ultimately culminated in the release of a 3.15.0 
kernel as the first el7 'GA' release.

For every subsequent new source code release, any new configuration 
options were again considered on a case by case basis. If the new option 
was part of a pre-existing option that was already enabled, then the new 
option would generally be enabled also.

Along the way many users have requested options be enabled within the 
kernel. These requests have generally been actioned unless deemed to be 
detrimental or otherwise not advisable. (Such requests should be made as 
RFEs's against the appropriate kernel package on elrepo.org/bugs 
otherwise they will be ignored).

The above process originally started out it's life as kernel-ml and then 
back in March 2016 forked to become kernel-lt with the release of 
kernel-lt-4.4.6.

The above process has been meticulously documented within the package 
changelog, which you can inspect in the (S)RPM or here:

https://github.com/elrepo/packages/blob/master/kernel-lt/el7/kernel-lt-4.4.spec

To understand the changes, you will need to individually review each in 
turn, reading the documentation for each as Alan has done over the last 
5+ years when making those decisions.

Hope that helps.

Phil