Add sched_getscheduler & sched_setscheduler

src/backend/libc/process/syscalls.rs

@@ -2,6 +2,8 @@
 
 #[cfg(any(freebsdlike, linux_kernel, target_os = "fuchsia"))]
 use super::types::RawCpuSet;
+#[cfg(any(freebsdlike, linux_kernel))]
+use super::types::{SchedParam, SchedPolicy};
 use crate::backend::c;
 #[cfg(not(any(target_os = "wasi", target_os = "fuchsia")))]
 use crate::backend::conv::borrowed_fd;
@@ -213,6 +215,29 @@ pub(crate) fn sched_setaffinity(pid: Option<Pid>, cpuset: &RawCpuSet) -> io::Res
     }
 }
 
+#[cfg(any(freebsdlike, linux_kernel))]
+#[inline]
+pub(crate) fn sched_getscheduler(pid: Option<Pid>) -> io::Result<SchedPolicy> {
+    unsafe { ret_c_int(c::sched_getscheduler(Pid::as_raw(pid) as _)) }
+        .map(|r| SchedPolicy::from_bits_retain(r as _))
+}
+
+#[cfg(any(freebsdlike, linux_kernel))]
+#[inline]
+pub(crate) fn sched_setscheduler(
+    pid: Option<Pid>,
+    policy: SchedPolicy,
+    param: &SchedParam,
+) -> io::Result<()> {
+    unsafe {
+        ret(c::sched_setscheduler(
+            Pid::as_raw(pid) as _,
+            policy.bits() as _,
+            core::ptr::from_ref(param) as _,
+        ))
+    }
+}
+
 #[inline]
 pub(crate) fn sched_yield() {
     unsafe {

src/backend/libc/process/types.rs

@@ -1,5 +1,7 @@
 #[cfg(not(any(target_os = "espidf", target_os = "vita")))]
 use crate::backend::c;
+#[cfg(any(freebsdlike, linux_kernel, target_os = "fuchsia"))]
+use bitflags::bitflags;
 
 /// A command for use with [`membarrier`] and [`membarrier_cpu`].
 ///
@@ -170,3 +172,52 @@ pub(crate) fn raw_cpu_set_new() -> RawCpuSet {
 
 #[cfg(any(freebsdlike, linux_kernel, target_os = "fuchsia"))]
 pub(crate) const CPU_SETSIZE: usize = c::CPU_SETSIZE as usize;
+
+#[cfg(any(freebsdlike, linux_kernel))]
+bitflags! {
+    /// `SCHED_*` constants for use with [`sched_getscheduler`] and [`sched_setscheduler`].
+    #[repr(transparent)]
+    #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
+    pub struct SchedPolicy: u32 {
+        /// `SCHED_OTHER`
+        #[cfg(not(target_os = "android"))] // not defined in android
+        const Other = c::SCHED_OTHER as u32;
+        /// `SCHED_FIFO`
+        const FIFO = c::SCHED_FIFO as u32;
+        /// `SCHED_RR`
+        const RoundRobin = c::SCHED_RR as u32;
+        /// `SCHED_BATCH`
+        #[cfg(linux_kernel)]
+        const Batch = c::SCHED_BATCH as u32;
+        /// `SCHED_IDLE`
+        #[cfg(linux_kernel)]
+        const Idle = c::SCHED_IDLE as u32;
+        /// `SCHED_DEADLINE`
+        #[cfg(target_os = "linux")] // not defined in android
+        const Deadline = c::SCHED_DEADLINE as u32;
+        /// `SCHED_RESET_ON_FORK`
+        #[cfg(target_os = "linux")] // not defined in android
+        const ResetOnFork = c::SCHED_RESET_ON_FORK as u32;
+        /// <https://docs.rs/bitflags/*/bitflags/#externally-defined-flags>
+        const _ = !0;
+    }
+}
+
+#[cfg(any(freebsdlike, linux_kernel))]
+impl Default for SchedPolicy {
+    fn default() -> Self {
+        #[cfg(not(target_os = "android"))]
+        return Self::Other;
+        #[cfg(target_os = "android")]
+        return Self::from_bits_retain(0);
+    }
+}
+
+/// `sched_param` for use with [`sched_getscheduler`] and [`sched_setscheduler`].
+#[cfg(any(freebsdlike, linux_kernel))]
+#[derive(Clone, Debug, Default)]
+#[repr(C)]
+pub struct SchedParam {
+    /// Scheduling priority.
+    pub sched_priority: i32,
+}

src/backend/linux_raw/process/syscalls.rs

@@ -5,7 +5,7 @@
 //! See the `rustix::backend` module documentation for details.
 #![allow(unsafe_code, clippy::undocumented_unsafe_blocks)]
 
-use super::types::RawCpuSet;
+use super::types::{RawCpuSet, SchedParam, SchedPolicy};
 use crate::backend::c;
 #[cfg(all(feature = "alloc", feature = "fs"))]
 use crate::backend::conv::slice_mut;
@@ -205,6 +205,33 @@ pub(crate) fn sched_yield() {
     }
 }
 
+#[inline]
+pub(crate) fn sched_getscheduler(pid: Option<Pid>) -> io::Result<SchedPolicy> {
+    unsafe {
+        ret_c_int(syscall_readonly!(
+            __NR_sched_getscheduler,
+            c_int(Pid::as_raw(pid))
+        ))
+    }
+    .map(|policy| SchedPolicy::from_bits_retain(bitcast!(policy)))
+}
+
+#[inline]
+pub(crate) fn sched_setscheduler(
+    pid: Option<Pid>,
+    policy: SchedPolicy,
+    param: &SchedParam,
+) -> io::Result<()> {
+    unsafe {
+        ret(syscall_readonly!(
+            __NR_sched_setscheduler,
+            c_int(Pid::as_raw(pid)),
+            c_uint(policy.bits()),
+            core::ptr::from_ref(param)
+        ))
+    }
+}
+
 #[cfg(feature = "fs")]
 #[inline]
 pub(crate) fn umask(mode: Mode) -> Mode {

src/backend/linux_raw/process/types.rs

@@ -1,3 +1,4 @@
+use bitflags::bitflags;
 use linux_raw_sys::general::membarrier_cmd;
 
 /// A command for use with [`membarrier`] and [`membarrier_cpu`].
@@ -102,3 +103,37 @@ pub(crate) fn raw_cpu_set_new() -> RawCpuSet {
 }
 
 pub(crate) const CPU_SETSIZE: usize = 8 * core::mem::size_of::<RawCpuSet>();
+
+bitflags! {
+    /// `SCHED_*` constants for use with [`sched_getscheduler`] and [`sched_setscheduler`].
+    #[repr(transparent)]
+    #[derive(Copy, Clone, Eq, PartialEq, Hash, Debug, Default)]
+    pub struct SchedPolicy: u32 {
+        /// `SCHED_OTHER`
+        const Other = 0;
+        /// `SCHED_FIFO`
+        const FIFO = 1;
+        /// `SCHED_RR`
+        const RoundRobin = 2;
+        /// `SCHED_BATCH`
+        const Batch = 3;
+        /// `SCHED_ISO`; only presented in some patched kernels.
+        const Isochronous = 4;
+        /// `SCHED_IDLE`
+        const Idle = 5;
+        /// `SCHED_DEADLINE`
+        const Deadline = 6;
+        /// `SCHED_RESET_ON_FORK`
+        const ResetOnFork = 0x40000000;
+        /// <https://docs.rs/bitflags/*/bitflags/#externally-defined-flags>
+        const _ = !0;
+    }
+}
+
+/// `sched_param` for use with [`sched_getscheduler`] and [`sched_setscheduler`].
+#[derive(Clone, Debug, Default)]
+#[repr(C)]
+pub struct SchedParam {
+    /// Scheduling priority.
+    pub sched_priority: i32,
+}

src/process/sched.rs

@@ -159,3 +159,45 @@ pub fn sched_getaffinity(pid: Option<Pid>) -> io::Result<CpuSet> {
 pub fn sched_getcpu() -> usize {
     backend::process::syscalls::sched_getcpu()
 }
+
+pub use backend::process::types::{SchedParam, SchedPolicy};
+
+/// `sched_getscheduler`—Get a thread's current scheduling policy.
+///
+/// `pid` is the thread ID to check. If pid is `None`, then the current thread
+/// is checked.
+///
+/// # References
+///  - [Linux]
+///  - [FreeBSD]
+///
+/// [Linux]: https://www.man7.org/linux/man-pages/man2/sched_setscheduler.2.html
+/// [FreeBSD]: https://man.freebsd.org/cgi/man.cgi?query=sched_setscheduler
+/// Other *BSD also support `sched_getscheduler`.
+#[cfg(any(freebsdlike, linux_kernel))]
+#[inline]
+pub fn sched_getscheduler(pid: Option<Pid>) -> io::Result<SchedPolicy> {
+    backend::process::syscalls::sched_getscheduler(pid)
+}
+
+/// `sched_setscheduler`—Set a thread's scheduling policy and parameters.
+///
+/// `pid` is the thread ID to set scheduling policy and parameters.
+/// If pid is `None`, then the target is the current thread.
+///
+/// # References
+///  - [Linux]
+///  - [FreeBSD]
+///
+/// [Linux]: https://www.man7.org/linux/man-pages/man2/sched_setscheduler.2.html
+/// [FreeBSD]: https://man.freebsd.org/cgi/man.cgi?query=sched_setscheduler
+/// Other *BSD also support `sched_setscheduler`.
+#[cfg(any(freebsdlike, linux_kernel))]
+#[inline]
+pub fn sched_setscheduler(
+    pid: Option<Pid>,
+    policy: SchedPolicy,
+    param: &SchedParam,
+) -> io::Result<()> {
+    backend::process::syscalls::sched_setscheduler(pid, policy, param)
+}

tests/process/sched.rs

@@ -12,3 +12,25 @@ fn test_sched_getcpu() {
     let n = rustix::process::sched_getcpu();
     assert!(n < rustix::process::CpuSet::MAX_CPU);
 }
+
+#[cfg(any(freebsdlike, linux_kernel))]
+#[test]
+fn test_sched_scheduler() {
+    use rustix::process::{SchedParam, SchedPolicy};
+
+    let policy = if cfg!(linux_kernel) {
+        SchedPolicy::Batch
+    } else {
+        // we cannot change policy in *BSD because we do not have priviledge
+        SchedPolicy::default()
+    };
+
+    // backup
+    let original_policy = rustix::process::sched_getscheduler(None).unwrap();
+
+    rustix::process::sched_setscheduler(None, policy, &SchedParam::default()).unwrap();
+    assert_eq!(rustix::process::sched_getscheduler(None).unwrap(), policy);
+
+    // restore
+    rustix::process::sched_setscheduler(None, original_policy, &SchedParam::default()).unwrap();
+}