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ostree-grub-generator: allow adding custom scripts to grub.cfg #3162

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EdTheBearded
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Hello!
I would like to propose this change here, since this may help someone else.

First the motivation for this change: rollback
We wanted to be able to perform a rollback if our update was unsuccessful in some way. And for that we needed to add some logic to grub.cfg script to get it done.

With that in mind, I tried to do this without changing too much or just manually editing grub.cfg. I took some inspiration on what grub-mkconfig does: check /etc/grub.d for custom scripts, and add those to the final grub.cfg script, parsing the files in their alphabetical order.

So with this change, whatever files found under /etc/ostree.d (just went with whatever name at the time) are added (in alphabetical order) between the cfg header and its menuentries, allowing to add custom logic to the bootloader in a non intrusive way.

NOTE: we're using this on Yocto, so there's also a minor change to be done in ostree recipe, to create the /etc folder being used.

This changes allow us to customize grub.cfg without manually editing it.

Now, whatever files found under /etc/ostree.d are added (in alphabetical
order) between the cfg header and its menuentries, allowing to add
custom logic to the bootloader in a non intrusive way.

Signed-off-by: Eduardo Ferreira <eduardo.barbosa@toradex.com>
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openshift-ci bot commented Feb 8, 2024

Hi @EdTheBearded. Thanks for your PR.

I'm waiting for a ostreedev member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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@cgwalters
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I'm not opposed exactly, but I don't quite understand. grub has a fully generic system for injecting code, why can't you drop your extra stuff into the existing /etc/grub.d?

On the topic of configuring rollbacks and grub configs, you may also want to look into https://github.com/coreos/bootupd/ which is intended to pair with ostree - bootupd supports an opinionated "static grub config" model where we don't regenerate any grub configs when updating the kernel, assuming GRUB has been patched to read from /boot/loader/entries directly.

Also, there is https://github.com/fedora-iot/greenboot/ (currently relies on rpm-ostree, not ostree, but that is conceptually a bug) which also now injects some grub logic via bootupd, see fedora-iot/greenboot#129

@@ -25,6 +25,7 @@ script=$(basename ${0})
# Atomically safe location where to generete grub.cfg when executing system upgrade.
new_grub2_cfg=${2}
entries_path=$(dirname $new_grub2_cfg)/entries
custom_scripts="/etc/ostree.d"
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This seems like it should be e.g. /etc/ostree-grub.d or so.

@cgwalters cgwalters added needinfo This issue needs more information from the reporter reviewed/needs-rework labels Feb 23, 2024
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