sys_util: Add ability to set real time thread priority

Add the minimal amount of functionality needed for audio threads that
need to run with real time priority.

Change-Id: I7052e0f2ba6b9179229fc4568b332952ee32f076
Signed-off-by: Dylan Reid <dgreid@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1366542
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Reviewed-by: David Tolnay <dtolnay@chromium.org>

2 files changed, 40 insertions, 0 deletions

diff --git a/sys_util/src/lib.rs b/sys_util/src/lib.rs
index 0172458..38fa81f 100644
--- a/sys_util/src/lib.rs
+++ b/sys_util/src/lib.rs
@@ -28,6 +28,7 @@ mod guest_memory;
 mod mmap;
 mod passwd;
 mod poll;
+mod priority;
 mod seek_hole;
 mod shm;
 pub mod signal;
@@ -51,6 +52,7 @@ pub use mmap::*;
 pub use passwd::*;
 pub use poll::*;
 pub use poll_token_derive::*;
+pub use priority::*;
 pub use shm::*;
 pub use signal::*;
 pub use signalfd::*;
diff --git a/sys_util/src/priority.rs b/sys_util/src/priority.rs
new file mode 100644
index 0000000..f65b9e0
--- /dev/null
+++ b/sys_util/src/priority.rs
@@ -0,0 +1,38 @@
+// Copyright 2018 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+use {errno_result, Result};
+
+/// Enables real time thread priorities in the current thread up to `limit`.
+pub fn set_rt_prio_limit(limit: u64) -> Result<()> {
+    let rt_limit_arg = libc::rlimit {
+        rlim_cur: limit as libc::rlim_t,
+        rlim_max: limit as libc::rlim_t,
+    };
+    // Safe because the kernel doesn't modify memory that is accessible to the process here.
+    let res = unsafe { libc::setrlimit(libc::RLIMIT_RTPRIO, &rt_limit_arg) };
+
+    if res != 0 {
+        errno_result()
+    } else {
+        Ok(())
+    }
+}
+
+/// Sets the current thread to be scheduled using the round robin real time class with `priority`.
+pub fn set_rt_round_robin(priority: i32) -> Result<()> {
+    let sched_param = libc::sched_param {
+        sched_priority: priority,
+    };
+
+    // Safe because the kernel doesn't modify memory that is accessible to the process here.
+    let res =
+        unsafe { libc::pthread_setschedparam(libc::pthread_self(), libc::SCHED_RR, &sched_param) };
+
+    if res != 0 {
+        errno_result()
+    } else {
+        Ok(())
+    }
+}