Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 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, |
Olivier Deprez | 0e64123 | 2021-09-23 10:07:05 +0200 | [diff] [blame] | 10 | unsigned long *flags, struct module *mod); |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 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, \ |
Olivier Deprez | 0e64123 | 2021-09-23 10:07:05 +0200 | [diff] [blame] | 49 | &___flags, THIS_MODULE); \ |
Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 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 */ |