Macro declare_scheduler

Source

declare_scheduler!() { /* proc-macro */ }

Expand description

Function-style macro that registers a Scheduler const.

§Syntax

use ktstr::prelude::*;

declare_scheduler!(MITOSIS, {
    name = "mitosis",
    binary = "scx_mitosis",
    cgroup_parent = "/ktstr",
    sched_args = ["--exit-dump-len", "1048576"],
    kernels = ["6.14", "7.0..=7.2"],
    constraints = TopologyConstraints {
        min_llcs: 1, max_llcs: Some(8), max_cpus: Some(64),
        ..TopologyConstraints::DEFAULT
    },
});

§Generated items

Given declare_scheduler!(MITOSIS, { ... }):

pub static MITOSIS: ::ktstr::test_support::Scheduler — the declared scheduler value. No _PAYLOAD suffix; the const IS the Scheduler.
A hidden static __KTSTR_SCHED_REG_MITOSIS: &'static Scheduler registered in KTSTR_SCHEDULERS (ktstr::test_support::KTSTR_SCHEDULERS) via linkme so the verifier can discover the declaration by spawning the test binary with --ktstr-list-schedulers.

§Visibility prefix

An optional Rust visibility prefix may precede the const name:

declare_scheduler!(MY_SCHED, { ... });             // defaults to `pub`
declare_scheduler!(pub MY_SCHED, { ... });          // explicit `pub`
declare_scheduler!(pub(crate) MY_SCHED, { ... });   // crate-local
declare_scheduler!(pub(super) MY_SCHED, { ... });   // parent-module
declare_scheduler!(pub(in crate::test_support) MY_SCHED, { ... });

Omitting the prefix defaults to pub — schedulers are normally public so the verifier and other crates can reference them; an explicit prefix is needed only when the declaration sits inside a module that wants to narrow the exposed name. (Field content shown above as { ... } is elided; consult the Syntax example for the required fields.) The hidden registry static (see Generated items above) is always static (private) regardless of the user-facing const’s visibility — linkme gathers it via link-section walking, not Rust name resolution, so the slice mechanism works at every visibility level.

§Accepted fields

Exactly one scheduler-source must be declared: binary, binary_path, or the kernel_builtin_enable + kernel_builtin_disable pair. The three options select between the matching SchedulerSpec variants. To run under the kernel default instead, reference ktstr::test_support::Scheduler::EEVDF directly rather than declaring a new scheduler.

Field	Required	Description
`name = "..."`	yes	Scheduler name (sidecar / logs).
`binary = "..."`	one source	Binary name → `SchedulerSpec::Discover(...)`. Matched against `[[bin]]` names in `target/{debug,release}/`, the test binary’s directory, or `KTSTR_SCHEDULER` env var. Often equal to the cargo package name but not required to be.
`binary_path = "/abs/path"`	one source	Absolute filesystem path → `SchedulerSpec::Path(...)`. The runtime does not auto-build this variant: the file must already exist at the path when the test runs. Use for prebuilt binaries that live outside the cargo discovery cascade. Macro-time validation rejects empty strings, relative paths, and `~`-prefixed paths (no compile-time tilde expansion); existence is the runtime’s job.
`kernel_builtin_enable = [..]` + `kernel_builtin_disable = [..]`	one source	Two string-array literals that together select `SchedulerSpec::KernelBuiltin { enable: &[..], disable: &[..] }`. The framework writes the enable commands to the guest’s `/sched_enable` and the disable commands to `/sched_disable` (see `src/vmm/initramfs.rs`), and the guest interpreter runs each entry once at scenario start / teardown. Both fields must be set together — setting only one is rejected. The interpreter (`src/vmm/rust_init/dump.rs`) accepts EXACTLY ONE shell-line shape: `echo VALUE > /path` (plus blank lines and `#` comments). Pipes, `>>`, `;`, variable expansion, and any other syntax silently no-ops at runtime, so the macro rejects entries that don’t match `echo … > /…` at expand time. At least one of the two arrays must be non-empty: a pair that supplies neither enable nor disable commands is equivalent to the EEVDF baseline — reference `Scheduler::EEVDF` for that. Note: `cargo ktstr export` currently bails on KernelBuiltin schedulers (`src/export.rs`); declarations using this variant cannot be reproduced via the export-to-shar workflow until that limitation is lifted.
`topology = (numa, llcs, cores, threads)`	no	Default VM topology. Default: `(1, 1, 2, 1)` (from `Scheduler::named`). Validated at compile time: each value must be non-zero, and `llcs` must be a multiple of `numa`.
`cgroup_parent = "..."`	no	Cgroup parent path (must begin with `/`).
`sched_args = [..]`	no	Scheduler CLI args prepended before per-test `extra_sched_args`.
`sysctls = [Sysctl::new("k", "v"), ..]`	no	Guest sysctls.
`kargs = [..]`	no	Extra guest kernel cmdline args.
`kernels = ["6.14", "7.0..=7.2", ..]`	no	Kernel specs the verifier sweeps. Same parser as the `--kernel` CLI flag — accepts exact versions, ranges (`..` or `..=`, both inclusive), git refs (`git+URL#tag=NAME`), paths, and cache keys. Each entry is validated at macro-expand time via the same `KernelId::parse` + `validate` the verifier uses at runtime; empty entries, inverted ranges, and `..`-containing strings whose endpoints aren’t version-shaped (e.g. `"abc..def"`) are rejected.
`constraints = TopologyConstraints { .. }`	no	Gauntlet preset constraints — maps directly onto `Scheduler::constraints`. Filters which gauntlet topology presets exercise this scheduler. When given as a struct literal, the macro additionally cross-checks each literal field against the effective topology (explicit `topology` field if present, otherwise the `(1, 1, 2, 1)` default from `Scheduler::named`) and rejects infeasible pairings; non-struct-literal forms (e.g. `OTHER::CONST_CONSTRAINTS`) skip that check.
`assert = Assert::NO_OVERRIDES.method().chain()`	no	Scheduler-wide assertion overrides — maps directly onto `Scheduler::assert`. Merged with `Assert::default_checks()` and the per-test `assert` at runtime (`default ← scheduler ← per-test`). Accepts any const-evaluable expression: a const path like `Assert::NO_OVERRIDES`, a const-fn call like `Assert::default_checks()`, or a chain of const-fn setters like `Assert::NO_OVERRIDES.check_not_starved().max_gap_ms(50)`. The macro accepts MethodCall chains and Path-rooted (type/module-prefixed) Calls — only bare single-segment lowercase Calls like `helper()` are rejected as non-const free-fn patterns; non-const methods on a Path receiver slip through and surface as a deep const-eval failure at the spread site.
`config_file = "..."`	no	Host-side config file path.
`config_file_def = ("--config {file}", "/include-files/cfg.json")`	no	Inline-config plumbing — maps directly onto `Scheduler::config_file_def`. 2-tuple of string literals: arg_template (CLI arg with `{file}` placeholder substituted at run time) and guest_path (absolute path where the framework writes the JSON inside the guest). Distinct from `config_file` (which references a pre-existing host file). The macro validates: tuple-arity = 2, both elements non-empty string literals, `{file}` placeholder present in arg_template, guest_path absolute.

§Const naming rules

The first argument must be a SCREAMING_SNAKE_CASE identifier and must NOT be one of the reserved built-in names (EEVDF, KERNEL_DEFAULT). The macro emits a compile_error! if either rule is violated.

declare_scheduler