`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

Spec	Section
`sched(7)` Linux man page	SCHED_OTHER / SCHED_FIFO / SCHED_RR / SCHED_DEADLINE
`sched_setattr(2)`	`sched_attr` struct + syscall number
`sched_setaffinity(2)`	`cpu_set_t`

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:

No pointer outliving — stack-local structs, no heap.
No FD leak — none of the syscalls used create FDs.
No memory aliasing — buffers are exclusive during the call.
Errno-to-Result — io::Error::last_os_error() is read exactly once before any further libc operations.
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

Feature	Default	Purpose
`std`	✅	`std::io::Error` + stack structs.

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.

zerodds-rt-linux 1.0.0-rc.3