[Lencerf]

Summary

Implement Virtio v1.4 Sec 5.10.6.3 (Buffer Space Management) stream flow-control credit accounting in UdsVsock:

• Peer credit tracking (tx_cnt, peer_buf_alloc, peer_fwd_cnt):
  • Track peer_buf_alloc and peer_fwd_cnt from incoming REQUEST, RESPONSE, RW, CREDIT_UPDATE, CREDIT_REQUEST, and SHUTDOWN headers.
  • Compute peer_free = peer_buf_alloc.saturating_sub((tx_cnt - peer_fwd_cnt).0), cap RX virtqueue RW payload reads to peer_free, and advance tx_cnt by each transmitted payload length.
  • Drive process_rx_data whenever incoming packets update peer credit so host-to-guest transfers stalled at peer_free == 0 immediately resume on edge-triggered mio sockets, while still observing host socket EOF when peer_free == 0.
• CREDIT_REQUEST handling:
  • Respond to VsockOp::CREDIT_REQUEST with VsockOp::CREDIT_UPDATE carrying current fwd_cnt and buf_alloc (deferring until an RX descriptor is available if the RX virtqueue is temporarily empty, and replying with RST for unknown connections).
• Unsolicited CREDIT_UPDATE on unidirectional guest TX:
  • Track last_fwd_cnt across outgoing packets and emit an unsolicited VsockOp::CREDIT_UPDATE once unacknowledged guest TX bytes reach half of buf_alloc, preventing unidirectional guest-to-host streams from stalling.

Testing

• cargo +nightly fmt --check
• cargo test -p alioth virtio::dev::vsock (13 unit tests in uds_vsock_test.rs, including new tests for CREDIT_REQUEST, RX peer_free flow control & resumption, unidirectional TX > buf_alloc / 96 KiB credit replenishment, and u32 counter wrap-around)
• cargo clippy --all-targets -- -D warnings
• cargo clippy --all-targets --target x86_64-unknown-linux-gnu -- -D warnings

[coveralls]

Coverage Report for CI Build 42955384191

Coverage increased (+0.5%) to 44.151%

Details

• Coverage increased (+0.5%) from the base build.
• Patch coverage: 15 uncovered changes across 1 file (201 of 216 lines covered, 93.06%).
• 2 coverage regressions across 1 file.

Uncovered Changes

File	Changed	Covered	%
alioth/src/virtio/dev/vsock/uds_vsock.rs	216	201	93.06%

Coverage Regressions

2 previously-covered lines in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
alioth/src/virtio/dev/vsock/uds_vsock.rs	2	82.85%

---

Coverage Stats

Relevant Lines:	16608
Covered Lines:	7121
Line Coverage:	42.88%
Relevant Branches:	1788
Covered Branches:	1001
Branch Coverage:	55.98%
Branches in Coverage %:	Yes
Coverage Strength:	924.9 hits per line

---

💛 - Coveralls