microvm-nix/microvm.nix

Use smbios to pass systemd credentials instead of fw_cfg

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#511 opened on Apr 27, 2026

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Description

According to https://github.com/systemd/systemd/issues/24204 https://github.com/systemd/systemd/blob/78208556b281bd6ee8a95d16a517152728010475/docs/CREDENTIALS.md?plain=1#L303

fw_cfg has a 55 bytes name length limit, and many systemd creds names are actually longer than that, e.g. opt/io.systemd.credentials/ssh.ephemeral-authorized_keys-all. SMBIOS is the new recommended way to pass in credentials.

Contributor guide

Research direction
Investigate the microvm.nix code where fw cfg is used for systemd credentials and replace it with SMBIOS based credential passing. Refer to systemd documentation for SMBIOS credential format.
Tech stack
None
Domain
backenddevops
Issue type
Refactor
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Nixsystemd
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40