[RFC] Updating boot loaders in lenny and squeeze

[Ben Hutchings <ben-/+tVBieCtBitmTQ+vhA3Yw@public.gmane.org>]

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Stephen Powell recently reminded the kernel team that LILO is not
automatically updated on installation of a new kernel version in lenny.
In fact there is a general problem that there are several different ways
a boot loader may be updated automatically and currently no guarantee
that this does happen whenever it should.

There are two major cases where a boot loader should be updated
automatically:

1. Where the boot loader relies on block lists rather than reading the
filesystem, these block lists need to be updated whenever a kernel image
or an initramfs is updated or removed.

2. Where the boot loader allows selection between arbitrarily many
installed versions, the configuration should be updated whenever a
kernel package is newly installed or removed.

There are several ways such updates may be triggered:

A. Packages built with older versions of kernel-package, including the
official kernel packages in etch, run a platform-specific default boot
loader if it is installed and if it falls into case 1 above.

B. The maintainer scripts of kernel packages invoke hook scripts
installed in appropriate subdirectories under /etc/kernel/.

C. The maintainer scripts of kernel packages invoke hook commands
specified in /etc/kernel-img.conf.

D. "update-initramfs -u" will run certain boot loader update programs if
installed.

In lenny, route A was effectively disabled in official kernel packages.
However, no boot loader uses route B and debian-installer enables route
C only for GRUB (as far as I know).  Disabling route A in lenny was
clearly premature and I intend to restore it in a stable update.

However, given that route B is present in both lenny and squeeze (and
even in etch, I think) there is no good reason for packages not to rely
on it now.  (Well, except lack of documentation.)  All boot loader
packages that fall into case 1 or 2 should be installing hook scripts,
but currently only extlinux does.  I intend to remove the vestigial code
for route A, and file bugs on all boot loaders in case 1 or 2 that do
not use route B.

In case 1, the boot loader should also be called by update-initramfs
when it is called outside of kernel package installation and removal.
This is normally covered by route D, but this seems a little fragile.  I
would prefer to replace this with a hook system (as already exists for
building the initramfs itself), but I'm not that involved in
initramfs-tools development.

Ben.

-- 
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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