[UNIKRAFT PATCH] include: Introduce uk/preemmpt.h

[Alexander Jung <a.jung@xxxxxxxxxxx>]

This commit adds an additional header with two new methods:

 - preempt_disable()
 - preempt_enable()

These methods enable and disable preemption by calling a memory
barrier only.  Their names are derived from the Linux Kernel[1].

Whilst currently unimplemented, pre-emptive scheduling requires
additional notarization when called.  This means that future
enhancements to Unikraft's pre-emptive scheduler will need to
modify these methods to increase a counter within the thread
to indicate whether the thread is pre-emptible or not.

[0]: https://elixir.bootlin.com/linux/latest/source/include/linux/preempt.h#L169

Signed-off-by: Alexander Jung <alexander.jung@xxxxxxxxx>
---
 include/uk/preempt.h | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 include/uk/preempt.h

diff --git a/include/uk/preempt.h b/include/uk/preempt.h
new file mode 100644
index 0000000..d45623d
--- /dev/null
+++ b/include/uk/preempt.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: BSD-3-Clause */
+/*
+ * Authors: Alexander Jung <alexander.jung@xxxxxxxxx>
+ *
+ * Copyright (c) 2020, NEC Laboratories Europe GmbH, NEC Corporation.
+ *                     All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the copyright holder nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef __UK_PREEMPT_H__
+#define __UK_PREEMPT_H__
+
+#define preempt_disable()      barrier()
+#define preempt_enable()       barrier()
+
+#endif /* __UK_PREEMPT_H__ */
-- 
2.11.0