qemu: Use --inode-file-handles=fallback for older virtiofsd compat

[cgwalters]

This is the new default, but needs to be turned on for older
versions that are shipped in the Ubuntu used in GHA.

Signed-off-by: Colin Walters walters@verbum.org

[gemini-code-assist]

Summary of Changes

Hello @cgwalters, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request primarily focuses on enhancing compatibility with older virtiofsd versions by introducing a specific fallback argument during its execution. Concurrently, it refactors the QemuConfig API by removing several redundant helper functions and their corresponding tests, aiming to simplify the configuration interface. The changes also consolidate the virtiofsd daemon spawning mechanism to an exclusively asynchronous approach.

Highlights

• Virtiofsd Compatibility: Added the --inode-file-handles=fallback argument to the virtiofsd command invocation within spawn_virtiofsd_async to ensure compatibility with older virtiofsd versions, specifically those found in Ubuntu GHA environments.
• QemuConfig Refactoring: Removed several helper methods from the QemuConfig struct, including new_disk_boot, add_virtio_blk_device, and add_virtiofs_mount, along with their associated unit tests. This streamlines the QemuConfig API.
• Asynchronous Virtiofsd Spawning: The synchronous spawn_virtiofsd function has been removed, consolidating all virtiofsd daemon spawning to the asynchronous spawn_virtiofsd_async function.

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[gemini-code-assist]

Code Review

This pull request introduces a compatibility fix for virtiofsd by adding the --inode-file-handles=fallback flag, which is necessary for older versions as noted in the description. The change is well-commented and justified. In addition to this fix, the pull request also performs significant code cleanup by removing several unused functions and their associated tests from QemuConfig. This refactoring simplifies the API and improves the overall maintainability of the code. The changes are well-executed and I see no issues.

[cgwalters]

OK, still failing in bootc-dev/bootc#1680 (comment) - but it's really weird that it only fails for fedora-{42,43} but not c{9,10}s. I wonder if there's something guest-specific going on here too.