linux-kernel - Re: [PATCH v3] docs: describe how to quickly build a trimmed kernel

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Message-ID: <b12d433e-62ea-3ac4-dd97-be0288f1335f@leemhuis.info>
Date:   Mon, 6 Mar 2023 10:07:26 +0100
From:   Thorsten Leemhuis <linux@...mhuis.info>
To:     Bagas Sanjaya <bagasdotme@...il.com>,
        Jonathan Corbet <corbet@....net>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        regressions@...ts.linux.dev
Subject: Re: [PATCH v3] docs: describe how to quickly build a trimmed kernel



On 06.03.23 09:57, Bagas Sanjaya wrote:
> On 3/6/23 12:40, Thorsten Leemhuis wrote:
>>> If your distro config have ``CONFIG_IKCONFIG=y``, you can copy from
>>> procfs::
>>>
>>>     zcat /proc/config.gz > .config
>> <snipped>
>>
>>> If it isn't the case, you may want to enable the aforementioned config
>>> option.
>>
>> That or put them in /boot/config-$(uname -r). But well, that is
>> something the provider of the running kernel needs to do, so it won't
>> help the reader if we mention it here.
>>
>> Or do you think the guide should explain this to ensure people can
>> pickup their config from there again in case they deleted their build
>> artifacts? Hmmm. I currently tend to think that's not worth making the
>> text longer for, as at that point it might be better to restart from
>> scratch with a distro config anyway.
>>
> 
> I think it depends whether someone would pick from /proc/config.gz or
> /boot/config. My kernel configuration have CONFIG_IKCONFIG=y but I
> often copy the config from the latter instead, since I booted with
> arbitrary kernel version when compiling two or three versions, and I
> want to ensure that the config used is from correct version (i.e.
> I use /boot/config-5.15.x-string to build 5.15.x+1 kernel).

Well, I'd say for most users the file that was automatically picked up
by olddefconfig/localmodconfig will be the right one. And for cases like
yours there is already this in the text:

```
The make targets try to find the configuration for your running kernel
automatically, but might choose poorly. A line like ‘# using defaults
found in /boot/config-6.0.7-250.fc36.x86_64’ or ‘using config:
‘/boot/config-6.0.7-250.fc36.x86_64’ tells you which file they picked.
If that is not the intended one, simply store it as ‘~/linux/.config’
before using these make targets.
```

Or am I missing something?

Ciao, Thorsten