feat(net): implement blocking recvfrom() with wait queues #114
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Implement proper blocking I/O for UDP sockets, replacing busy-wait with efficient wait queues. DNS test pass rate improved from ~30% to 100%. Key changes: - Add waiting_threads queue to UdpSocket for blocked thread tracking - Implement wake mechanism in enqueue_packet() when packets arrive - Add blocking HLT loop in sys_recvfrom() with proper preemption handling - Fix idle thread context restoration after userspace starts - Add ready_queue duplicate prevention in scheduler - Add unit tests for wait queue and scheduler invariants The idle context fix was critical: after userspace starts (RING3_CONFIRMED), idle always goes to idle_loop instead of restoring potentially stale boot-time context that could cause hangs. Also adds Docker test scripts for DNS, keyboard, and interactive testing. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
CRITICAL: Running QEMU directly on macOS causes system-wide instability: - Hypervisor.framework resource leaks when QEMU is killed - GPU driver destabilization affecting all GPU-accelerated apps - Memory pressure cascades from orphaned QEMU processes This update makes Docker-based QEMU execution mandatory: - All QEMU runs must use docker/qemu/run-*.sh scripts - GDB debugging is now disabled (requires native QEMU) - Added new test scripts: run-dns-test.sh, run-interactive.sh Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
…tions Handler tests: - test_is_ring3_confirmed_initial_state: Verify false before Ring 3 syscalls - test_ring3_confirmed_swap_behavior: Verify exactly-once detection semantics Socket tests: - test_recvfrom_error_constants: Verify EAGAIN, EBADF, ENOTSOCK constants - test_sockaddr_in_structure: Verify sockaddr_in layout and byte conversion - test_socket_type_constants: Verify AF_INET, SOCK_STREAM, SOCK_DGRAM values - test_udp_socket_has_data_for_race_check: Verify has_data() for race fix NOTE: These are no_std kernel tests that compile as part of the kernel build but cannot run with cargo test due to x86_64-breenix target. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Add #[allow(dead_code)] annotations for code that is only used in conditionally-compiled build configurations: - kernel_main_continue: only called when not dns_test_only - Async executor infrastructure (Task, TaskId, Executor, TaskWaker): only used when async keyboard/serial tasks are enabled - keyboard_task and related functions: conditionally compiled - serial_command_task and related functions: conditionally compiled - TTY input_char path and helpers: used by keyboard_task - Timer validation functions: used in kernel_main_continue - TSC query functions: used in debug and test code - UdpSocket::set_nonblocking: public API for future fcntl support Also adds #[cfg] annotation to kernel_main_continue to match its call site, preventing compilation when not needed. Build is now warning-free for the dns_test_only configuration. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Add unit tests recommended by validation report: - test_enqueue_packet_wakes_multiple_waiters: Verify all waiting threads are woken when packet arrives - test_nonblocking_mode_flag: Test set_nonblocking() behavior - test_recv_from_dequeues_packets: Test FIFO ordering of packet receive - test_race_condition_double_check: Test the critical double-check pattern that prevents race between setting Blocked state and packet arrival - test_rx_queue_overflow: Test oldest-packet-dropped behavior at queue limit Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
- Add SOCK_NONBLOCK (0x800) flag support in sys_socket() - Mask nonblocking flag from base socket type before type switch - Add SOCK_NONBLOCK constant to libbreenix socket module - Fix EAGAIN test to use SOCK_DGRAM | SOCK_NONBLOCK Integration test: - Add blocking_recv_test userspace binary that creates blocking UDP socket and waits for external packet - Add run-blocking-recv-test.sh Docker script with UDP port forwarding - Add blocking_recv_test feature flag to kernel Cargo.toml Test improvements from validation: - Rename test_has_data_double_check_pattern to test_has_data_reflects_queue_state - Add module-level documentation explaining unit test limitations - Document that true concurrent race testing requires integration tests All tests pass: - DNS test: 6/6 stages - Blocking recv test: PASS - Boot test: PASS Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
… test Address validation review findings: Critical fixes: - Add nonblock_eagain_test.rs integration test that verifies SOCK_NONBLOCK creates a non-blocking socket that returns EAGAIN when no data available - Strengthen blocking_recv_test.rs to verify received data starts with "wakeup" (the string sent by test script), fail with exit code 4 on mismatch Important fixes: - Add test_recvfrom_ebadf_constant unit test documenting EBADF error value and noting syscall error paths require process context All tests pass: - DNS test: 6/6 stages - Blocking recv test: PASS (with data verification) - Nonblock EAGAIN test: exercises SOCK_NONBLOCK path - Boot test: PASS Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Summary
recvfrom()has no data available → block the calling threadThis follows the existing stdin blocking pattern in the kernel and replaces the inefficient busy-wait loop in DNS resolution.
Key Changes
Core Implementation
UdpSocketfor tracking blocked threadsregister_waiter()/unregister_waiter()/wake_waiters()methodssys_recvfrom()to block when no data and socket is blocking modeenqueue_packet()when data arrivesSOCK_NONBLOCK Support
SOCK_NONBLOCK(0x800) flag support insys_socket()socket(AF_INET, SOCK_DGRAM | SOCK_NONBLOCK, 0)Integration Testing
blocking_recv_test.rsuserspace binary - creates blocking UDP socket on port 55556run-blocking-recv-test.shDocker script with UDP port forwardingnc -u localhost 55556wakes blocked testUnit Tests
has_data()double-check patternTest plan
./docker/qemu/run-dns-test.sh- All 6 stages pass./docker/qemu/run-blocking-recv-test.sh- PASS (thread blocks, wakes on packet)./docker/qemu/run-boot-parallel.sh 1- Full boot test passescargo build --release- Zero warnings🤖 Generated with Claude Code