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1 | #ifndef _LINUX_ONCE_H | |
2 | #define _LINUX_ONCE_H | |
3 | ||
4 | #include <linux/types.h> | |
5 | #include <linux/jump_label.h> | |
6 | ||
7 | bool __do_once_start(bool *done, unsigned long *flags); | |
8 | void __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 */ |