Merge #1148

1148: Implement sched::sched_getaffinity() r=asomers a=thib-ack

Hello,

I found the function `sched::sched_setaffinity()` but I also needed to get the process affinity and I did not find the function `sched::sched_getaffinity()`
So I added the function which maps [sched_getaffinity(2)](https://linux.die.net/man/2/sched_getaffinity) which "get a process's CPU affinity mask" to the sched.rs file.
I hope the code match your guidelines (returned `Result<CpuSet>` instead of pointer parameter)
If that's not the case, tell me, I will fix asap.

I hope this will help !

Thanks,
Thibaut

Co-authored-by: Thibaut Ackermann <thibaut@ackermann.dev>

2 files changed, 35 insertions, 0 deletions

diff --git a/test/test.rs b/test/test.rs
index 24260500..4b13fa44 100644
--- a/test/test.rs
+++ b/test/test.rs
@@ -119,6 +119,9 @@ mod test_nix_path;
 mod test_poll;
 mod test_pty;
 #[cfg(any(target_os = "android",
+          target_os = "linux"))]
+mod test_sched;
+#[cfg(any(target_os = "android",
           target_os = "freebsd",
           target_os = "ios",
           target_os = "linux",
diff --git a/test/test_sched.rs b/test/test_sched.rs
new file mode 100644
index 00000000..922196a3
--- /dev/null
+++ b/test/test_sched.rs
@@ -0,0 +1,32 @@
+use nix::sched::{sched_getaffinity, sched_setaffinity, CpuSet};
+use nix::unistd::Pid;
+
+#[test]
+fn test_sched_affinity() {
+    // If pid is zero, then the mask of the calling process is returned.
+    let initial_affinity = sched_getaffinity(Pid::from_raw(0)).unwrap();
+    let mut at_least_one_cpu = false;
+    let mut last_valid_cpu = 0;
+    for field in 0..CpuSet::count() {
+        if initial_affinity.is_set(field).unwrap() {
+            at_least_one_cpu = true;
+            last_valid_cpu = field;
+        }
+    }
+    assert!(at_least_one_cpu);
+
+    // Now restrict the running CPU
+    let mut new_affinity = CpuSet::new();
+    new_affinity.set(last_valid_cpu).unwrap();
+    sched_setaffinity(Pid::from_raw(0), &new_affinity).unwrap();
+
+    // And now re-check the affinity which should be only the one we set.
+    let updated_affinity = sched_getaffinity(Pid::from_raw(0)).unwrap();
+    for field in 0..CpuSet::count() {
+        // Should be set only for the CPU we set previously
+        assert_eq!(updated_affinity.is_set(field).unwrap(), field==last_valid_cpu)
+    }
+
+    // Finally, reset the initial CPU set
+    sched_setaffinity(Pid::from_raw(0), &initial_affinity).unwrap();
+}