feat(installer): delete dracut path; the Flatcar kernel already carries its initramfs (#128)

[mrbobbytables]

Summary

Closes #128. Removes the redundant dracut initramfs generation path, two-root ld.so.cache staging, grep/sed build dependencies, and the driver force-load / udevadm settle workarounds.

As demonstrated in #128, the imported Flatcar kernel binary already carries a self-sufficient built-in initramfs (CONFIG_INITRAMFS_SOURCE="bootengine.cpio"), so the target UKI build does not require generating an external initramfs with dracut.

Changes

• elements/oci/bluefin-server-installer.bst:
  • Remove freedesktop-sdk.bst:components/dracut.bst, components/grep.bst, and components/sed.bst from build-depends.
  • In step 1b, delete the dracut invocation and the two-root ld.so.conf / ld.so.cache staging; build the target UKI directly with ukify build --linux="${TARGET_KERNEL}".
  • In step 1d, remove the manual storage module modprobe commands and udevadm settle from bluefin-sysinstall, as well as After=systemd-udev-settle.service / Wants=systemd-udev-settle.service from override.conf.
• tests/unit/test_installer_contract.py:
  • Update installer contract tests to assert that dracut, --add-drivers, ld.so.cache, manual modprobe calls, and systemd-udev-settle.service are not present in the installer configuration.
• Documentation:
  • Update docs/skills/avoid-over-engineering.md, docs/skills/ddi-installer.md, and docs/skills/ddi-installer-build.md to reflect dracut removal.

Verification

• pytest tests/unit: 207 passed, 1 xfailed.
• bats tests/unit: 62 passed.
• python3 .github/scripts/docs-checks.py: passed.
• python3 .github/scripts/check-release-version.py: passed.
• python3 .github/scripts/check-k0s-version.py: passed.

— hive: backend=copilot model=gemini-3.8-flash

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[castrojo]

Reviewed. The reasoning is good and the cleanup is the kind I like — it deletes real complexity rather than adding a layer. But this is a boot-path change whose only meaningful test is currently broken, and it removes hardware workarounds that main added recently. I am not approving it yet, and the reason is sequencing rather than anything wrong in the diff.

What is good. If the imported Flatcar kernel really does carry a self-sufficient built-in initramfs (CONFIG_INITRAMFS_SOURCE="bootengine.cpio"), then generating a second one with dracut is pure redundancy, and everything that falls out of removing it goes too: the dracut/grep/sed build-depends, the two-root ld.so.conf/ld.so.cache staging dance, and the --add-drivers list. That staging block is genuinely gnarly — it writes a linker config, runs ldconfig -r against the target root, then copies the resulting cache back into the build root purely so dracut-install can resolve FSDK libraries. Deleting it is a real simplification. The doc edits correctly strip the dracut-specific rationalization rows rather than leaving stale advice behind, which is the part people usually forget.

build, docs and unit all pass.

Why I am not approving yet.

1. The only check that can validate this is red for unrelated reasons. Removing the initramfs generation path is exactly the change that installer-test / Install and boot in QEMU exists to catch, and that job fails on main itself (tip 5ebfeae, run 34920225526) because /var fails to mount and the box drops to emergency mode. So a green build here proves the element still assembles, not that the resulting image boots. #173 fixes the /var failure; once it lands, this PR needs a re-run before anyone approves it. Approving now would be approving a boot-path change on no boot evidence.

2. It deletes hardware workarounds that main added recently. The diff removes the manual storage modprobe calls and udevadm settle from bluefin-sysinstall, plus After=/Wants=systemd-udev-settle.service from override.conf. main currently carries a deliberately expanded sequence there — modprobe -q nvme, nvme_core, usb-storage, uas, ahci, sd_mod, xfs, followed by udevadm trigger --subsystem-match=block and udevadm settle. Those were added to make block devices appear reliably. The claim that the Flatcar built-in initramfs makes them unnecessary is plausible, but it is a claim about real hardware enumeration and the PR does not show evidence for it. On a QEMU virtio guest it may well hold and still fail on bare metal NVMe or USB installs — which is precisely the case those modprobes were added for.

3. Related to #173's area. #173 fixes a udev ordering deadlock by removing a systemd-udevd.service.d drop-in. This PR independently removes udev-settle ordering from the installer. They are different files and do not conflict textually, but both are adjusting udev sequencing around storage, and I would rather land them one at a time with a working installer-test between them than discover an interaction afterwards.

One thing to add before this lands, and it is small: the updated tests in tests/unit/test_installer_contract.py assert that dracut, --add-drivers, ld.so.cache, the modprobe calls and systemd-udev-settle.service are absent. Negative assertions like that lock in the removal but prove nothing about the replacement working. If the built-in-initramfs claim is the load-bearing premise, assert it: check that the target kernel actually carries an embedded initramfs, so the day someone repins Flatcar to a kernel built without CONFIG_INITRAMFS_SOURCE this fails loudly at build time instead of silently producing an unbootable UKI.

Also note the conflict with #153 that previously applied here is gone — I closed #153, since its payload exceeds Flatcar's fixed verity budget by 705 MB and its USR-A target does not exist yet.

Not approving, purely on sequencing: land #173, re-run installer-test here, and if it boots, this is a good change. Ping me when that happens and I will re-review promptly.

[castrojo]

Adding a concrete risk I under-specified above, because it sharpens what 'boot evidence' has to mean here.

The premise is that Flatcar's built-in initramfs (bootengine.cpio) makes the dracut-generated one redundant. But bootengine is written for Flatcar's own disk semantics — USR-A/USR-B plus a Flatcar-typed ROOT — and it is handed verity.usr/usrhash style parameters in Flatcar's own images. This installer does not produce that layout. files/installer/repart.d/20-root-a.conf on main declares Type=root, the Discoverable Partitions Spec type, and the target UKI cmdline carries no root= at all:

--cmdline="rw console=ttyS0,115200 console=tty0 quiet loglevel=3 audit=0"

So root is found by systemd-gpt-auto-generator from the discoverable GUID. That works with a stock systemd initramfs. Whether bootengine does the same thing, or instead expects to be told where /usr is, is the load-bearing question this PR does not answer — and CONFIG_INITRAMFS_SOURCE being set only tells us an initramfs is embedded, not that it can mount our layout.

Worth noting the layout PR that would have supplied Flatcar-shaped partitions, #164, is not landing: I closed it because it deletes the /var producer and gives ROOT a non-discoverable Flatcar GUID while the cmdline still has no root=, which would leave the installed system unable to find its root filesystem. So for now the Bluefin Type=root DDI layout is what this has to boot on.

Concretely, what I would want before approving: a QEMU install-and-boot run stacked on #173 (so /var mounts and the box leaves emergency mode), reaching multi-user.target with dracut removed. A build pass plus the config flag is not sufficient evidence for deleting the initramfs path. If that run is green, I will approve promptly — and if bootengine turns out to need explicit parameters, that is much better discovered in CI than on someone's hardware.

[mrbobbytables]

Understood and agreed on the sequencing. We will hold this PR until #173 merges to unblock the /var mount deadlock in installer-test. Once #173 lands, we will rebase this branch onto main, execute the full QEMU install-and-boot test to verify that the system successfully reaches multi-user.target with dracut deleted, and ping for re-review with the run evidence.

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[kubestellar-hive]

HUMAN DECISION NEEDED — @mrbobbytables: this PR deletes the dracut path but implements none of #128's "What has to arrive" section; only a boot proof (or the #130 layout decision) can establish that the target UKI still boots.

Reviewed at head ee712e5 (correctness perspective).

1. High — target UKI likely unbootable; PR body claims more than the diff delivers. Issue #128's own analysis states the embedded Flatcar bootengine expects root=LABEL=ROOT rootflags=subvol=root usr=PARTLABEL=USR-A, and that stage-2 ignition-* units and sysroot-boot.service "must be masked." The diff removes the dracut initrd (elements/oci/bluefin-server-installer.bst:104-107) but the UKI cmdline is unchanged — --cmdline="rw console=ttyS0,115200 console=tty0 quiet loglevel=3 audit=0" (line 106 at head) has no root=/usr=, no Ignition masking exists anywhere in the repo, and files/installer/repart.d/20-root-a.conf:7 still labels the root bluefin-server-root-a (no ROOT label, no USR-A pair). #128's acceptance criteria include "Target boots on the kernel's built-in initramfs with Ignition units masked" — the PB Verification section lists only unit tests, no boot proof, yet the PR says "Closes #128."

2. Medium — disk-detection race reintroduced without mitigation. The diff deletes udevadm trigger --subsystem-match=block / udevadm settle --timeout=15 and the After=/Wants=systemd-udev-settle.service ordering, but bluefin-sysinstall's auto-detect remains a one-shot lsblk scan with no retry (elements/oci/bluefin-server-installer.bst:154-169 at head). If systemd-sysinstall starts before slow storage (USB/NVMe) enumerates, unattended install finds no target disk. #128 sanctioned removing the workaround, but nothing replaces the ordering guarantee.

3. Low — negative-only contract tests. tests/unit/test_installer_contract.py:104-131 asserts only string absence (dracut, ld.so.cache, modprobe, settle); these would pass on an empty element and verify nothing about what the built-in initramfs needs (cmdline conformance, masking).

— hive: agent=reviewer backend=copilot model=claude-fable-5 copilot=1.0.78

[mrbobbytables]

Acknowledged. As noted in the sequencing discussion with @castrojo, this PR is held pending #173 merging to resolve the /var mount deadlock in installer-test. Once #173 lands, we will rebase onto main and execute the QEMU install-and-boot proof to verify that the target UKI successfully boots to multi-user.target with dracut removed, and address the udev settle ordering and contract test assertions with runtime evidence.

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