zerodds-rt-linux

Linux real-time scheduling adapter for the ZeroDDS stack: SCHED_FIFO/SCHED_RR/ SCHED_DEADLINE profiles + CPU pinning. Safety classification: COMFORT — the only place in the workspace where unsafe syscalls reach the runtime path.

Spec mapping

No OMG spec — Linux kernel API.

What's inside

• SchedulerProfile — builder for SCHED_FIFO/SCHED_RR/ SCHED_DEADLINE/SCHED_OTHER profiles with validation.
• SchedulerKind — enum discriminants.
• apply_to_current_thread() — sched_setattr on tid=0.
• current_scheduler() — sched_getattr on tid=0, returns RunningSchedulerInfo.
• pin_current_thread_to_cpus(&[u32]) — sched_setaffinity with a CPU set.

On non-Linux targets all public APIs return io::ErrorKind::Unsupported — the workspace still builds on macOS and Windows.

Layer position

Layer 4 — core services. No ZeroDDS crate deps; libc is the only external dep, target-gated cfg(target_os = "linux").

Quickstart

use zerodds_rt_linux::{SchedulerProfile, pin_current_thread_to_cpus};

// Real-time FIFO with priority 80, CPU pinning to cores 2+3:
let profile = SchedulerProfile::fifo(80).expect("priority valid");
profile.apply_to_current_thread().expect("CAP_SYS_NICE needed");
pin_current_thread_to_cpus(&[2, 3]).expect("affinity set");

Privileges

SCHED_FIFO/SCHED_RR with priority > 0 + SCHED_DEADLINE need CAP_SYS_NICE (effective). Default-user tests get EPERM back — the test suite treats this as "skipped" and does not claim the path is verified.

Threat model + invariants

All FFI calls in this crate hold the following invariants:

1. No pointer outliving — stack-local structs, no heap.
2. No FD leak — none of the syscalls used create FDs.
3. No memory aliasing — buffers are exclusive during the call.
4. Errno-to-Result — io::Error::last_os_error() is read exactly once before any further libc operations.
5. No mut-aliasing race — all calls refer to tid = 0 (the calling thread), not foreign threads.

Every unsafe { libc::... } block in syscalls.rs carries a // SAFETY: comment with a block-specific rationale.

Feature flags

Without std the crate builds as a no-op stub on Linux (all public APIs return Unsupported).

Stability

1.0.0-rc.1. Public API + errno mapping RC1-stable. The Linux kernel API (sched_setattr/sched_setaffinity) has been stable since kernel 3.14.

Tests

cargo test -p zerodds-rt-linux

7 tests — privilege-free paths + EPERM errno paths + round-trip between apply and current_scheduler.

License

Apache-2.0. See LICENSE.

See also

• sched(7), sched_setattr(2), sched_setaffinity(2) — Linux man pages.
• docs/architecture/04_safety_by_architecture.md §2.3 COMFORT class.