syslet: asm-generic support to disable syslets

This provides an implementation of the architecture dependent portion of
syslets which disables syslet operations.

This patch is an incomplete demonstration.  All asm-*/syslet*.h files would
include these files until their architectures provide implementations which
enable syslet support. 

Signed-off-by: Zach Brown <zach.brown@oracle.com>

---
 include/asm-generic/syslet-abi.h |   11 +++++++++++
 include/asm-generic/syslet.h     |   34 ++++++++++++++++++++++++++++++++++
 include/asm-x86/syslet-abi.h     |    1 +
 include/asm-x86/syslet.h         |    1 +
 4 files changed, 47 insertions(+), 0 deletions(-)

diff --git a/include/asm-generic/syslet-abi.h b/include/asm-generic/syslet-abi.h
new file mode 100644
index 0000000..5d19971
--- /dev/null
+++ b/include/asm-generic/syslet-abi.h
@@ -0,0 +1,11 @@
+#ifndef _ASM_GENERIC_SYSLET_ABI_H
+#define _ASM_GENERIC_SYSLET_ABI_H
+
+/*
+ * I'm assuming that a u64 ip and u64 esp won't be enough for all
+ * archs, so I just let each arch define its own.
+ */
+struct syslet_frame {
+};
+
+#endif
diff --git a/include/asm-generic/syslet.h b/include/asm-generic/syslet.h
new file mode 100644
index 0000000..de9a750
--- /dev/null
+++ b/include/asm-generic/syslet.h
@@ -0,0 +1,34 @@
+#ifndef _ASM_GENERIC_SYSLET_H
+#define _ASM_GENERIC_SYSLET_H
+
+/*
+ * This provider of the arch-specific syslet APIs is used when an architecture
+ * doesn't support syslets.
+ */
+
+/* this stops the other functions from ever being called */
+static inline int syslet_frame_valid(struct syslet_frame *frame)
+{
+	return 0;
+}
+
+static inline void set_user_frame(struct task_struct *task,
+				  struct syslet_frame *frame)
+{
+	BUG();
+}
+
+static inline void move_user_context(struct task_struct *dest,
+					struct task_struct *src)
+{
+	BUG();
+}
+
+static inline int create_syslet_thread(long (*fn)(void *),
+				       void *arg, unsigned long flags)
+{
+	BUG();
+	return 0;
+}
+
+#endif
diff --git a/include/asm-x86/syslet-abi.h b/include/asm-x86/syslet-abi.h
new file mode 100644
index 0000000..14a7182
--- /dev/null
+++ b/include/asm-x86/syslet-abi.h
@@ -0,0 +1 @@
+#include <asm-generic/syslet-abi.h>
diff --git a/include/asm-x86/syslet.h b/include/asm-x86/syslet.h
new file mode 100644
index 0000000..583d810
--- /dev/null
+++ b/include/asm-x86/syslet.h
@@ -0,0 +1 @@
+#include <asm-generic/syslet.h>