From f332cf96d4c30cbd8886a3b37eec26ee5c03b305 Mon Sep 17 00:00:00 2001
From: Jonas 'Sortie' Termansen <sortie@maxsi.org>
Date: Mon, 16 Sep 2013 21:16:35 +0200
Subject: [PATCH] Add sched_yield(2).

---
 kernel/include/sortix/syscallnum.h |  3 ++-
 kernel/scheduler.cpp               |  6 +++++
 libc/Makefile                      |  1 +
 libc/include/sched.h               | 36 ++++++++++++++++++++++++++++++
 libc/sched/sched_yield.cpp         | 34 ++++++++++++++++++++++++++++
 5 files changed, 79 insertions(+), 1 deletion(-)
 create mode 100644 libc/include/sched.h
 create mode 100644 libc/sched/sched_yield.cpp

diff --git a/kernel/include/sortix/syscallnum.h b/kernel/include/sortix/syscallnum.h
index a1720bd7..c182a1cc 100644
--- a/kernel/include/sortix/syscallnum.h
+++ b/kernel/include/sortix/syscallnum.h
@@ -152,6 +152,7 @@
 #define SYSCALL_FSTATVFSAT 128
 #define SYSCALL_RDMSR 129
 #define SYSCALL_WRMSR 130
-#define SYSCALL_MAX_NUM 131 /* index of highest constant + 1 */
+#define SYSCALL_SCHED_YIELD 131
+#define SYSCALL_MAX_NUM 132 /* index of highest constant + 1 */
 
 #endif
diff --git a/kernel/scheduler.cpp b/kernel/scheduler.cpp
index 1d73a2dc..7b6d6df1 100644
--- a/kernel/scheduler.cpp
+++ b/kernel/scheduler.cpp
@@ -311,6 +311,11 @@ static int sys_usleep(size_t usecs)
 	return 0;
 }
 
+static int sys_sched_yield(void)
+{
+	return kthread_yield(), 0;
+}
+
 void Init()
 {
 	premagic = postmagic = SCHED_MAGIC;
@@ -329,6 +334,7 @@ void Init()
 
 	Syscall::Register(SYSCALL_SLEEP, (void*) sys_sleep);
 	Syscall::Register(SYSCALL_USLEEP, (void*) sys_usleep);
+	Syscall::Register(SYSCALL_SCHED_YIELD, (void*) sys_sched_yield);
 }
 
 } // namespace Scheduler
diff --git a/libc/Makefile b/libc/Makefile
index 8ecf0c18..323cb714 100644
--- a/libc/Makefile
+++ b/libc/Makefile
@@ -339,6 +339,7 @@ pwd/getpwuid.o \
 pwd/getpwuid_r.o \
 pwd/openpw.o \
 pwd/setpwent.o \
+sched/sched_yield.o \
 signal/kill.o \
 signal/killpg.o \
 signal/psignal.o \
diff --git a/libc/include/sched.h b/libc/include/sched.h
new file mode 100644
index 00000000..f969976c
--- /dev/null
+++ b/libc/include/sched.h
@@ -0,0 +1,36 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2013, 2014.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or (at your
+    option) any later version.
+
+    The Sortix C Library is distributed in the hope that it will be useful, but
+    WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+    or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    sched.h
+    Executing scheduling.
+
+*******************************************************************************/
+
+#ifndef INCLUDE_SCHED_H
+#define INCLUDE_SCHED_H
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+int sched_yield(void);
+
+__END_DECLS
+
+#endif
diff --git a/libc/sched/sched_yield.cpp b/libc/sched/sched_yield.cpp
new file mode 100644
index 00000000..664d87a1
--- /dev/null
+++ b/libc/sched/sched_yield.cpp
@@ -0,0 +1,34 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2013, 2014.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or (at your
+    option) any later version.
+
+    The Sortix C Library is distributed in the hope that it will be useful, but
+    WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+    or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    sched/sched_yield.cpp
+    Yields control of the CPU so another thread can run.
+
+*******************************************************************************/
+
+#include <sys/syscall.h>
+
+#include <sched.h>
+
+DEFN_SYSCALL0(int, sys_sched_yield, SYSCALL_SCHED_YIELD);
+
+extern "C" int sched_yield(void)
+{
+	return sys_sched_yield();
+}