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 | /* Helpers used from arbitrary contexts. |
9 | * Hard irqs are blocked, be cautious. |
10 | */ |
11 | bool __do_once_start(bool *done, unsigned long *flags); |
12 | void __do_once_done(bool *done, struct static_key_true *once_key, |
13 | unsigned long *flags, struct module *mod); |
14 | |
15 | /* Variant for process contexts only. */ |
16 | bool __do_once_sleepable_start(bool *done); |
17 | void __do_once_sleepable_done(bool *done, struct static_key_true *once_key, |
18 | struct module *mod); |
19 | |
20 | /* Call a function exactly once. The idea of DO_ONCE() is to perform |
21 | * a function call such as initialization of random seeds, etc, only |
22 | * once, where DO_ONCE() can live in the fast-path. After @func has |
23 | * been called with the passed arguments, the static key will patch |
24 | * out the condition into a nop. DO_ONCE() guarantees type safety of |
25 | * arguments! |
26 | * |
27 | * Note that the following is not equivalent ... |
28 | * |
29 | * DO_ONCE(func, arg); |
30 | * DO_ONCE(func, arg); |
31 | * |
32 | * ... to this version: |
33 | * |
34 | * void foo(void) |
35 | * { |
36 | * DO_ONCE(func, arg); |
37 | * } |
38 | * |
39 | * foo(); |
40 | * foo(); |
41 | * |
42 | * In case the one-time invocation could be triggered from multiple |
43 | * places, then a common helper function must be defined, so that only |
44 | * a single static key will be placed there! |
45 | */ |
46 | #define DO_ONCE(func, ...) \ |
47 | ({ \ |
48 | bool ___ret = false; \ |
49 | static bool __section(".data.once") ___done = false; \ |
50 | static DEFINE_STATIC_KEY_TRUE(___once_key); \ |
51 | if (static_branch_unlikely(&___once_key)) { \ |
52 | unsigned long ___flags; \ |
53 | ___ret = __do_once_start(&___done, &___flags); \ |
54 | if (unlikely(___ret)) { \ |
55 | func(__VA_ARGS__); \ |
56 | __do_once_done(&___done, &___once_key, \ |
57 | &___flags, THIS_MODULE); \ |
58 | } \ |
59 | } \ |
60 | ___ret; \ |
61 | }) |
62 | |
63 | /* Variant of DO_ONCE() for process/sleepable contexts. */ |
64 | #define DO_ONCE_SLEEPABLE(func, ...) \ |
65 | ({ \ |
66 | bool ___ret = false; \ |
67 | static bool __section(".data.once") ___done = false; \ |
68 | static DEFINE_STATIC_KEY_TRUE(___once_key); \ |
69 | if (static_branch_unlikely(&___once_key)) { \ |
70 | ___ret = __do_once_sleepable_start(&___done); \ |
71 | if (unlikely(___ret)) { \ |
72 | func(__VA_ARGS__); \ |
73 | __do_once_sleepable_done(&___done, &___once_key,\ |
74 | THIS_MODULE); \ |
75 | } \ |
76 | } \ |
77 | ___ret; \ |
78 | }) |
79 | |
80 | #define get_random_once(buf, nbytes) \ |
81 | DO_ONCE(get_random_bytes, (buf), (nbytes)) |
82 | |
83 | #define get_random_sleepable_once(buf, nbytes) \ |
84 | DO_ONCE_SLEEPABLE(get_random_bytes, (buf), (nbytes)) |
85 | |
86 | #endif /* _LINUX_ONCE_H */ |
87 | |