unix: add SchedSetAttr and SchedGetAttr for Linux

Add wrappers for sched_getattr(2) and sched_setattr(2), as well as
various SCHED_ values usable for these.

The kludge in linux/types.go is needed so we can include both
linux/sched/types.h (for struct sched_attr) and sched.h (for a few
defines from include/bits/cpu-set.h).

Unfortunately, they both define struct sched_param, thus the need to
mask one of the definitions.

Change-Id: I3e13cf49ccef7ae81a75d33826d18de84a52106d
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Reviewed-on: https://go-review.googlesource.com/c/sys/+/516756
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>

unix/syscall_linux.go

@@ -2471,6 +2471,29 @@ func Pselect(nfd int, r *FdSet, w *FdSet, e *FdSet, timeout *Timespec, sigmask *
 	return pselect6(nfd, r, w, e, mutableTimeout, kernelMask)
 }
 
+//sys	schedSetattr(pid int, attr *SchedAttr, flags uint) (err error)
+//sys	schedGetattr(pid int, attr *SchedAttr, size uint, flags uint) (err error)
+
+// SchedSetAttr is a wrapper for sched_setattr(2) syscall.
+// https://man7.org/linux/man-pages/man2/sched_setattr.2.html
+func SchedSetAttr(pid int, attr *SchedAttr, flags uint) error {
+	if attr == nil {
+		return EINVAL
+	}
+	attr.Size = SizeofSchedAttr
+	return schedSetattr(pid, attr, flags)
+}
+
+// SchedGetAttr is a wrapper for sched_getattr(2) syscall.
+// https://man7.org/linux/man-pages/man2/sched_getattr.2.html
+func SchedGetAttr(pid int, flags uint) (*SchedAttr, error) {
+	attr := &SchedAttr{}
+	if err := schedGetattr(pid, attr, SizeofSchedAttr, flags); err != nil {
+		return nil, err
+	}
+	return attr, nil
+}
+
 /*
  * Unimplemented
  */