unix: add SchedGetaffinity and SchedSetaffinity on Linux

SchedGetaffinity and SchedSetaffinity are used to get and set a thread's
CPU affinity mask.

See http://man7.org/linux/man-pages/man2/sched_setaffinity.2.html for
details.

Also add a manual implementation of CpuSet_t and the corresponding
accessor functions (mimicking the CPU_* macros from sched.h).

Fixes golang/go#11243

Change-Id: Ia5abc0053cd06810b3b09ab65c27434f5323c1ad
Reviewed-on: https://go-review.googlesource.com/85915
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/syscall_linux_test.go

@@ -9,6 +9,7 @@ package unix_test
 import (
 	"io/ioutil"
 	"os"
+	"runtime"
 	"testing"
 	"time"
 
@@ -255,6 +256,58 @@ func TestFstatat(t *testing.T) {
 	}
 }
 
+func TestSchedSetaffinity(t *testing.T) {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	var oldMask unix.CPUSet
+	err := unix.SchedGetaffinity(0, &oldMask)
+	if err != nil {
+		t.Fatalf("SchedGetaffinity: %v", err)
+	}
+
+	var newMask unix.CPUSet
+	newMask.Zero()
+	if newMask.Count() != 0 {
+		t.Errorf("CpuZero: didn't zero CPU set: %v", newMask)
+	}
+	cpu := 1
+	newMask.Set(cpu)
+	if newMask.Count() != 1 || !newMask.IsSet(cpu) {
+		t.Errorf("CpuSet: didn't set CPU %d in set: %v", cpu, newMask)
+	}
+	cpu = 5
+	newMask.Set(cpu)
+	if newMask.Count() != 2 || !newMask.IsSet(cpu) {
+		t.Errorf("CpuSet: didn't set CPU %d in set: %v", cpu, newMask)
+	}
+	newMask.Clear(cpu)
+	if newMask.Count() != 1 || newMask.IsSet(cpu) {
+		t.Errorf("CpuClr: didn't clear CPU %d in set: %v", cpu, newMask)
+	}
+
+	err = unix.SchedSetaffinity(0, &newMask)
+	if err != nil {
+		t.Fatalf("SchedSetaffinity: %v", err)
+	}
+
+	var gotMask unix.CPUSet
+	err = unix.SchedGetaffinity(0, &gotMask)
+	if err != nil {
+		t.Fatalf("SchedGetaffinity: %v", err)
+	}
+
+	if gotMask != newMask {
+		t.Errorf("SchedSetaffinity: returned affinity mask does not match set affinity mask")
+	}
+
+	// Restore old mask so it doesn't affect successive tests
+	err = unix.SchedSetaffinity(0, &oldMask)
+	if err != nil {
+		t.Fatalf("SchedSetaffinity: %v", err)
+	}
+}
+
 // utilities taken from os/os_test.go
 
 func touch(t *testing.T, name string) {