1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_ONCE_H
3 #define _LINUX_ONCE_H
4
5 #include <linux/types.h>
6 #include <linux/jump_label.h>
7
8 bool __do_once_start(bool *done, unsigned long *flags);
9 void __do_once_done(bool *done, struct static_key_true *once_key,
10 unsigned long *flags);
11
12 /* Call a function exactly once. The idea of DO_ONCE() is to perform
13 * a function call such as initialization of random seeds, etc, only
14 * once, where DO_ONCE() can live in the fast-path. After @func has
15 * been called with the passed arguments, the static key will patch
16 * out the condition into a nop. DO_ONCE() guarantees type safety of
17 * arguments!
18 *
19 * Not that the following is not equivalent ...
20 *
21 * DO_ONCE(func, arg);
22 * DO_ONCE(func, arg);
23 *
24 * ... to this version:
25 *
26 * void foo(void)
27 * {
28 * DO_ONCE(func, arg);
29 * }
30 *
31 * foo();
32 * foo();
33 *
34 * In case the one-time invocation could be triggered from multiple
35 * places, then a common helper function must be defined, so that only
36 * a single static key will be placed there!
37 */
38 #define DO_ONCE(func, ...) \
39 ({ \
40 bool ___ret = false; \
41 static bool ___done = false; \
42 static DEFINE_STATIC_KEY_TRUE(___once_key); \
43 if (static_branch_unlikely(&___once_key)) { \
44 unsigned long ___flags; \
45 ___ret = __do_once_start(&___done, &___flags); \
46 if (unlikely(___ret)) { \
47 func(__VA_ARGS__); \
48 __do_once_done(&___done, &___once_key, \
49 &___flags); \
50 } \
51 } \
52 ___ret; \
53 })
54
55 #define get_random_once(buf, nbytes) \
56 DO_ONCE(get_random_bytes, (buf), (nbytes))
57 #define get_random_once_wait(buf, nbytes) \
58 DO_ONCE(get_random_bytes_wait, (buf), (nbytes)) \
59
60 #endif /* _LINUX_ONCE_H */