Enable Dracut's livenet rootfs handling when systemd-networkd is in use.

[gmileka]

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• The toolchain has been rebuilt successfully (or no changes were made to it)
• The toolchain/worker package manifests are up-to-date
• Any updated packages successfully build (or no packages were changed)
• Packages depending on static components modified in this PR (Golang, *-static subpackages, etc.) have had their Release tag incremented.
• Package tests (%check section) have been verified with RUN_CHECK=y for existing SPEC files, or added to new SPEC files
• All package sources are available
• cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json, .github/workflows/cgmanifest.json)
• LICENSE-MAP files are up-to-date (./LICENSES-AND-NOTICES/SPECS/data/licenses.json, ./LICENSES-AND-NOTICES/SPECS/LICENSES-MAP.md, ./LICENSES-AND-NOTICES/SPECS/LICENSE-EXCEPTIONS.PHOTON)
• All source files have up-to-date hashes in the *.signatures.json files
• sudo make go-tidy-all and sudo make go-test-coverage pass
• Documentation has been updated to match any changes to the build system
• Ready to merge

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Summary

Dracut provides a livenet module which allows the downloading of a liveos ISO image from a PXE server at boot time. However, this functionality is not implemented for systemd-networkd in Dracut 102 and earlier (see bug and fix).

It is desired to produce Azure Linux liveos ISO images that are PXE-ready. To enable this scenario, we need to ensure that Dracut's livenet module is functional on Azure Linux images.

There are two options:

1. Upgrade dracut version to 103+.
2. Patch the current Dracut version.

Given that Azure Linux has GA'ed, and given that Dracut introduced refactoring around the networking supported between 102 and 103, we opted to minimize the risk of upgrading at this time and go with patching the current Dracut version.

This change augments Dracut's livenet module with a daemon to be started when the network is up. The new daemon will then call the livenet module download script.

Regression Risk

Minimal.

To avoid side effects or conflicts with existing user configuration, this flow is only activated if the new rd.live.azldownloader kernel parameter is present and set to 'enabled' - otherwise, it is not activated.

Change Log

• Update dracut livenet module with an iso downloader script to enable PXE booting for liveos ISOs.

Does this affect the toolchain?

• no

Associated issues

• 9741

Links to CVEs

• n/a

Test Methodology

Unit Tests

• Ran MIC liveos ISO tests (tests include coverage for new scenario).

Functional Tests

• Deploy a PXE server on the network.
• Use MIC to generate a liveos iso (vhdx->iso) and specify the new --output-pxe-artifacts-dir parameter.
  • Attach the iso to a hyper-v VM
    • Verify the VM boots, and the user can log-in.
  • Deploy the iso artifacts to a PXE server and boot a PXE client on the same network.
    • Verify the PXE client boots, and that the user can log-in.
• Use MIC to generate a liveos iso (iso->iso) and specify the new --output-pxe-artifacts-dir parameter.
  • Attach the iso to a hyper-v VM
    • Verify the VM boots, and the user can log-in.
  • Deploy the iso artifacts to a PXE server and boot a PXE client on the same network.
    • Verify the PXE client boots, and that the user can log-in.
    • Verify user settings from the first run (vhdx-iso) have been retained.