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Re: [RFC] flash-kernel hook to prepend to boot script

On Wed, 2014-05-21 at 14:59 -0600, dann frazier wrote:
> hey,
>  A couple of projects we're working on at work require some
> tweaking of u-boot settings. These requirements can be summed up by:
>  A) Maintain the console= setting, and ideally all userargs (the
>     cmdline args after "--") after install. This seems like standard
>     Debian functionality that exists on other architectures, but is
>     currently missing on flash-kernel platforms. 
>  B) The ability to let a package change settings in the u-boot
>     environment. We have a case where a u-boot envvar setting
>     needs to differ depending on whether or not certain software
>     will be used (their u-boot has special code that reconfigures
>     the hardware depending on the setting of this variable).
> The systems we're dealing with use a boot.scr script generated by
> flash-kernel. So, we figure we could solve both by letting packages
> drop in u-boot code snippets that will be prepended to the
> boot.scr. To do this, we propose a scheme similar to initramfs-tools
> where packages can drop snippets in a path under /usr/share (solving
> B), and users can add their own new setings or override the /usr/share
> versions by dropping snippets under /etc. With this scheme in place,
> flash-kernel-installer could be extended to drop in a file in /etc
> that does a 'setenv bootargs $userargs' to solve (A). Comments?

I think snippets like this are a useful idea in general, but I wonder if
something like the command line isn't deserving of "higher billing",
e.g. via a setting in /etc/defaults/flash-kernel:COMMAND_LINE?

FWIW latest Debian flash-kernel supports substituting @@KERNEL_VERSION@@
in the boot.scr with the actual kernel version in use. We could follow a
similar path for command line args (e.g. if you agree /e/d/flash-kernel
is a good place for this setting).

> +user_params="$(echo $(user-params))"

What does this contain in practice? Just the post "--" stuff given to
the installer or also the generated root= stuff etc?

How does this interact with the Bootloader-Sets-Incorrect-Root setting?
Should it consume the same settings somehow (assuming root= is involved
here at all)?


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