Re: [RFC] flash-kernel hook to prepend to boot script
On Tue, May 27, 2014 at 10:35:18AM -0600, dann frazier wrote:
> On Mon, May 26, 2014 at 11:54:31AM +0100, Ian Campbell wrote:
> > 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 $userargs' to solve (A). Comments?
> >
> > I think snippets like this are a useful idea in general, but I wonder if
> > something like the command line isn't deserving of "higher billing",
> > e.g. via a setting in /etc/defaults/flash-kernel:COMMAND_LINE?
>
> It looks like Ubuntu is carrying a patch that does this today:
>
> http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/utopic/flash-kernel/utopic/revision/443.2.7
>
> There the the variable is called "UBOOT_DEFAULTS". I think
> "KERNEL_CMDLINE" would be a more obvious name, but it would also be
> nice to be reducing their diff.
Looking at grub as an example, I think we'll want to make the cmdline
paramaters a debconf setting, giving the user the option to modify the
proposed cmdline in expert mode.
1) f-k-i would use user-params to generate a reasonable default set
cmdline args and set flash-kernel/linux_cmdline.
2) f-k/configure would prompt the user (priority=high) for changes to
this default during configuration.
3) f-k/postinst would generate /etc/default/flash-kernel, and
presumably using ucf to manage it from there on
Sound reasonable?
-dann
> > FWIW latest Debian flash-kernel supports substituting @@KERNEL_VERSION@@
> > in the boot.scr with the actual kernel version in use. We could follow a
> > similar path for command line args (e.g. if you agree /e/d/flash-kernel
> > is a good place for this setting).
>
> Yeah, that makes sense. For non-cmdline options, should we make that a
> substitution as well (e.g. @@UBOOT_ENV_EXTRA@@), or automatically prepend
> the snippets for every boot.scr? The former might be nice if we want
> to transition platforms over individually as we can test them. But,
> the downside is inconsistency until then.
>
> > > +user_params="$(echo $(user-params))"
> >
> > What does this contain in practice? Just the post "--" stuff given to
> > the installer or also the generated root= stuff etc?
>
> Just the post "--" stuff. It also works with preseeding
> (debian-installer/add-kernel-opts).
>
> > 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)?
>
> It looks like that logic is all in an initramfs hook, so there should
> be no interaction there.
>
>
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