1#ifndef _LINUX_ONCE_H
2#define _LINUX_ONCE_H
3
4#include <linux/types.h>
5#include <linux/jump_label.h>
6
7bool __do_once_start(bool *done, unsigned long *flags);
8void __do_once_done(bool *done, struct static_key *once_key,
9		    unsigned long *flags);
10
11/* Call a function exactly once. The idea of DO_ONCE() is to perform
12 * a function call such as initialization of random seeds, etc, only
13 * once, where DO_ONCE() can live in the fast-path. After @func has
14 * been called with the passed arguments, the static key will patch
15 * out the condition into a nop. DO_ONCE() guarantees type safety of
16 * arguments!
17 *
18 * Not that the following is not equivalent ...
19 *
20 *   DO_ONCE(func, arg);
21 *   DO_ONCE(func, arg);
22 *
23 * ... to this version:
24 *
25 *   void foo(void)
26 *   {
27 *     DO_ONCE(func, arg);
28 *   }
29 *
30 *   foo();
31 *   foo();
32 *
33 * In case the one-time invocation could be triggered from multiple
34 * places, then a common helper function must be defined, so that only
35 * a single static key will be placed there!
36 */
37#define DO_ONCE(func, ...)						     \
38	({								     \
39		bool ___ret = false;					     \
40		static bool ___done = false;				     \
41		static struct static_key ___once_key = STATIC_KEY_INIT_TRUE; \
42		if (static_key_true(&___once_key)) {			     \
43			unsigned long ___flags;				     \
44			___ret = __do_once_start(&___done, &___flags);	     \
45			if (unlikely(___ret)) {				     \
46				func(__VA_ARGS__);			     \
47				__do_once_done(&___done, &___once_key,	     \
48					       &___flags);		     \
49			}						     \
50		}							     \
51		___ret;							     \
52	})
53
54#define get_random_once(buf, nbytes)					     \
55	DO_ONCE(get_random_bytes, (buf), (nbytes))
56
57#endif /* _LINUX_ONCE_H */
58