The Nixpkgs documentation on the linux kernel builders focused on
using and extending kernels that were already packaged, but never
mentioned that it's possible to also build a kernel almost "from
scratch".
The NixOS documentation went a bit deeper on manual linux kernel
configs, but that information wasn't particularly NixOS-specific.
This commit consolidates the information related to building the
kernel on Nixpkgs's documentation, while keeping any additional
NixOS-specific information on NixOS's documentation.
An additional README.md was created for contributor-facing
documentation.
Document the `linux.override` way first, then `linuxManualConfig`.
Add a `linux.configEnv` passthru attribute for quickly getting a
`make nconfig`-ready shell.
I'm well aware that this issue is currently under discussion[1] and that
these things may change. Also, please don't misinterpret this as an
attempt to end the discussion.
This topic made it obvious that people are surprised by the way this
issue is handled and only finding out about this unwritten rule because
of asking is not a good state IMHO, so I decided to document the
following things:
* Right now we drop kernels as soon as they get out of maintenance (LTS
kernels even before the next stable NixOS that will exceed their
lifespan).
* The `latestCompatibleLinuxPackages` attribute from ZFS isn't
monotonic since latest only refers to the latest supported kernel.
* In fact `latestCompatibleLinuxPackages` doesn't seem to be documented
at all in the manual, so I also did that.
[1] https://discourse.nixos.org/t/aggressive-kernel-removal-on-eol-in-nixos/23097
