[plug] kernels and Debain versions

[Craig Ringer]

On Sun, 2004-03-21 at 15:16, smclevie wrote:

> Q1.  When does a kernel drop away features of earlier kernels?
>          is it when the second number changes? ie 4 to 6 in 2.4.24 to 2.6.4

Yes, though occasionally some things (such as drivers) are dropped
within a stable release. It's not common to drop features at all,
though.

>          (Related Q) How far back/forward is a kernel compatible?  ie a can 
> a person running 2.2.20 suddenly jump to 2.6.4??

Yes, so long as they make sure any userspace changes that are needed
have been made. For example, 2.6.x requires a new modutils to work.
These requirements are documented in Documentation/Changes ; if they're
met, it should be fine. Please note that occasionally some of the tools
may prove hard to build on very old distros.

> Q2.  Is a Debian 'suite' limited or best suited to any version of kernel?
>          eg.  is 'stable' limited to say kernels 2.2.20 through to 2.4.24 ?
>          this would imply that if you want to use the latest kernels you 
> should be running 'testing' ...

No, but as above you may need to upgrade some userspace tools. If you
want to do this the 'debian way' you must find backports of the tools,
or upgrade to a prerelease Debian.

> Q3.  During a kernel build, one can select a large number of options in 
> menuconfig ...
>          But how do you know what options are the same as the option in a 
> previous kernel??
>          eg say in kernel 2.4.24 an option equates to thingymejig.o ....
>          what in kernel 2.6.4 equates to thingamejig.o ???
>          Do you then have to inspect/compare the config file in /boot all 
> the time?
>          This file is never twice the same !!!  It is a real organisational 
> mess !!!

Not sure. I've never found it to be an issue, frankly. Usually driver
names don't change, so if you configured it in 2.4 you should be able to
in 2.6. Otherwise ... reading the built-in help, noting what modules you
currently have loaded and therefore obviously need, and if you have to a
little trial and error should do the trick. Alternately, the
kernel-source-[blah] Debian packages should come pre-configued with
sensible defaults.

Craig Ringer