Add additional backend tests

[pykello]

Summary

• extend backend tests to cover configuration and feature methods
• exercise acked_features, set_event_idx(false), queues_per_thread and update_memory
• verify VirtioBlockConfig returned by get_config

Testing

• cargo test --quiet
• cargo llvm-cov --no-report --ignore-filename-regex src/bin/

---

https://chatgpt.com/codex/tasks/task_e_68892e46d760832787e188c00a960ccb

[greptile-apps]

Greptile Summary

This PR adds comprehensive test coverage for the UbiBlkBackend's VhostUserBackend trait implementation. The changes extend the existing test suite in backend_tests.rs to cover previously untested methods that are critical for vhost-user protocol compliance.

The new tests exercise five key areas:

1. Feature advertisement (features()) - Validates that essential Virtio features like VIRTIO_F_VERSION_1 and VIRTIO_RING_F_EVENT_IDX are properly advertised
2. Feature acknowledgment (acked_features()) - Tests the logging mechanism when features are acknowledged by the guest
3. Event index management (set_event_idx()) - Verifies that event indexing can be disabled across all worker threads
4. Configuration retrieval (get_config()) - Tests the binary serialization of the VirtioBlockConfig structure using unsafe pointer casting to reconstruct and validate the configuration
5. Queue distribution (queues_per_thread()) - Validates the bit-mask calculation logic that determines how queues are assigned to threads

All tests follow proper Rust testing patterns with setup, execution, and assertion phases. They use the existing TestBlockDevice for isolation and create realistic test scenarios. The tests are particularly important because they verify the backend's ability to correctly communicate with hypervisors through the vhost-user protocol, ensuring proper feature negotiation and device configuration exposure.

Confidence score: 4/5

• This PR is very safe to merge as it only adds test coverage without changing production code behavior
• The score reflects high confidence due to comprehensive test coverage of critical vhost-user protocol methods with no production code changes
• No files need additional attention - the tests are well-structured and isolated

_{1 file reviewed, no comments}

_{Edit Code Review Bot Settings | Greptile}