These changes are the raw update to linux-4.4.6-rt14. Kernel sources

[kvmfornfv.git] / kernel / include / linux / once.h

diff --git a/kernel/include/linux/once.h b/kernel/include/linux/once.h
new file mode 100644 (file)
index 0000000..285f12c
--- /dev/null
+++ b/kernel/include/linux/once.h
@@ -0,0 +1,57 @@
+#ifndef _LINUX_ONCE_H
+#define _LINUX_ONCE_H
+
+#include <linux/types.h>
+#include <linux/jump_label.h>
+
+bool __do_once_start(bool *done, unsigned long *flags);
+void __do_once_done(bool *done, struct static_key *once_key,
+                   unsigned long *flags);
+
+/* Call a function exactly once. The idea of DO_ONCE() is to perform
+ * a function call such as initialization of random seeds, etc, only
+ * once, where DO_ONCE() can live in the fast-path. After @func has
+ * been called with the passed arguments, the static key will patch
+ * out the condition into a nop. DO_ONCE() guarantees type safety of
+ * arguments!
+ *
+ * Not that the following is not equivalent ...
+ *
+ *   DO_ONCE(func, arg);
+ *   DO_ONCE(func, arg);
+ *
+ * ... to this version:
+ *
+ *   void foo(void)
+ *   {
+ *     DO_ONCE(func, arg);
+ *   }
+ *
+ *   foo();
+ *   foo();
+ *
+ * In case the one-time invocation could be triggered from multiple
+ * places, then a common helper function must be defined, so that only
+ * a single static key will be placed there!
+ */
+#define DO_ONCE(func, ...)                                                  \
+       ({                                                                   \
+               bool ___ret = false;                                         \
+               static bool ___done = false;                                 \
+               static struct static_key ___once_key = STATIC_KEY_INIT_TRUE; \
+               if (static_key_true(&___once_key)) {                         \
+                       unsigned long ___flags;                              \
+                       ___ret = __do_once_start(&___done, &___flags);       \
+                       if (unlikely(___ret)) {                              \
+                               func(__VA_ARGS__);                           \
+                               __do_once_done(&___done, &___once_key,       \
+                                              &___flags);                   \
+                       }                                                    \
+               }                                                            \
+               ___ret;                                                      \
+       })
+
+#define get_random_once(buf, nbytes)                                        \
+       DO_ONCE(get_random_bytes, (buf), (nbytes))
+
+#endif /* _LINUX_ONCE_H */