[Lencerf]

Summary

Fixes two critical issues in Alioth's vhost and vhost-user frontend implementations:

1. Packed virtqueue SET_VRING_BASE wrap counter initialization:

   • Per VirtIO 1.4 Sec 2.8.1, both the driver and device ring wrap counters in packed virtqueues are initialized to 1.
   • When VIRTIO_F_RING_PACKED is negotiated, vhost and vhost-user SET_VRING_BASE encode avail_wrap_counter in bit 15 and used_wrap_counter in bit 31.
   • Update VuFrontend::activate and VhostVsock::activate to set initial base to (1 << 15) | (1 << 31) for packed rings (0 for split rings).

2. VuFrontend feature filtering and VMM crash prevention:

   • Filter VuFrontend::feature() to expose only supported VirtIO transport features (INDIRECT_DESC, EVENT_IDX, VERSION_1, ACCESS_PLATFORM, RING_PACKED) alongside device-specific feature bits (0..24 and 50..64), stripping VHOST_PROTOCOL (bit 30) and unsupported transport/reserved bits (24..50). Also strip VHOST_PROTOCOL in VhostVsock::new and only include VHOST_PROTOCOL in VuFrontend::activate SET_FEATURES when advertised by the backend.
   • Replace unreachable!() in VuFrontend::handle_event with vu_error::QueueErr (draining the error eventfd on error and reset so re-activation does not loop), and replace unreachable!() in VuFrontend::handle_queue and VhostVsock::handle_queue with kick notification forwarding or error logging so unexpected notifications never crash the VMM.

Testing

• Added unit tests in alioth/src/virtio/vu/frontend_test.rs and alioth/src/virtio/dev/vsock/vhost_vsock_test.rs covering split vs. packed SET_VRING_BASE, conditional VHOST_PROTOCOL in SET_FEATURES, feature bit filtering, queue error event handling, and unexpected queue notification handling.
• Verified both commits individually with cargo +nightly fmt --check, cargo test --workspace, cargo clippy --all-targets -- -D warnings, and cargo clippy --all-targets --target x86_64-unknown-linux-gnu -- -D warnings.

[coveralls]

Coverage Report for CI Build 42955106147

Coverage increased (+0.9%) to 44.521%

Details

• Coverage increased (+0.9%) from the base build.
• Patch coverage: 8 uncovered changes across 2 files (46 of 54 lines covered, 85.19%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
alioth/src/virtio/dev/vsock/vhost_vsock.rs	19	15	78.95%
alioth/src/virtio/vu/frontend.rs	35	31	88.57%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	16477
Covered Lines:	7133
Line Coverage:	43.29%
Relevant Branches:	1764
Covered Branches:	988
Branch Coverage:	56.01%
Branches in Coverage %:	Yes
Coverage Strength:	906.94 hits per line

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💛 - Coveralls