Kernel package tips & tricks.

		~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The kernel is one of the more complicated packages in the distro, and

for the newcomer, some of the voodoo in the spec file can be somewhat scary.

This file attempts to document some of the magic.

Speeding up make prep

---------------------

The kernel is nearly 500MB of source code, and as such, 'make prep'

takes a while. The spec file employs some trickery so that repeated

invocations of make prep don't take as long.  Ordinarily the %prep

phase of a package will delete the tree it is about to untar/patch.

The kernel %prep keeps around an unpatched version of the tree,

and makes a symlink tree clone of that clean tree and than applies

the patches listed in the spec to the symlink tree.

This makes a huge difference if you're doing multiple make preps a day.

As an added bonus, doing a diff between the clean tree and the symlink

tree is slightly faster than it would be doing two proper copies of the tree.

build logs.

-----------

There's a convenience helper script in scripts/grab-logs.sh

that will grab the build logs from koji for the kernel version reported

by make verrel

config heirarchy.

-----------------

Instead of having to maintain a config file for every arch variant we build on,

the kernel spec uses a nested system of configs.  At the top level, is

config-generic. Add options here that should be present in every possible

config on all architectures.

Beneath this are per-arch overrides. For example config-x86-generic add

additional x86 specific options, and also _override_ any options that were

set in config-generic.

There exist two additional overrides, config-debug, and config-nodebug,

which override -generic, and the per-arch overrides. It is documented

further below.

debug options.

--------------

This is a little complicated, as the purpose & meaning of this changes

depending on where we are in the release cycle.

If we are building for a current stable release, 'make release' has

typically been run already, which sets up the following..

- Two builds occur, a 'kernel' and a 'kernel-debug' flavor.

- kernel-debug will get various heavyweight debugging options like

  lockdep etc turned on.

If we are building for rawhide, 'make debug' has been run, which changes

the status quo to:

- We only build one kernel 'kernel'

- The debug options from 'config-debug' are always turned on.

This is done to increase coverage testing, as not many people actually

run kernel-debug.

To add new debug options, add an option to _both_ config-debug and config-nodebug,

and also new stanzas to the Makefile 'debug' and 'release' targets.

Sometimes debug options get added to config-generic, or per-arch overrides

instead of config-[no]debug. In this instance, the options should have no

discernable performance impact, otherwise they belong in the debug files.