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60 lines
1.8 KiB
60 lines
1.8 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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#ifndef _LINUX_ONCE_H |
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#define _LINUX_ONCE_H |
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#include <linux/types.h> |
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#include <linux/jump_label.h> |
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bool __do_once_start(bool *done, unsigned long *flags); |
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void __do_once_done(bool *done, struct static_key_true *once_key, |
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unsigned long *flags); |
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/* Call a function exactly once. The idea of DO_ONCE() is to perform |
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* a function call such as initialization of random seeds, etc, only |
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* once, where DO_ONCE() can live in the fast-path. After @func has |
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* been called with the passed arguments, the static key will patch |
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* out the condition into a nop. DO_ONCE() guarantees type safety of |
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* arguments! |
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* |
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* Not that the following is not equivalent ... |
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* |
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* DO_ONCE(func, arg); |
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* DO_ONCE(func, arg); |
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* |
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* ... to this version: |
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* |
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* void foo(void) |
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* { |
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* DO_ONCE(func, arg); |
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* } |
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* |
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* foo(); |
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* foo(); |
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* |
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* In case the one-time invocation could be triggered from multiple |
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* places, then a common helper function must be defined, so that only |
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* a single static key will be placed there! |
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*/ |
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#define DO_ONCE(func, ...) \ |
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({ \ |
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bool ___ret = false; \ |
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static bool ___done = false; \ |
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static DEFINE_STATIC_KEY_TRUE(___once_key); \ |
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if (static_branch_unlikely(&___once_key)) { \ |
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unsigned long ___flags; \ |
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___ret = __do_once_start(&___done, &___flags); \ |
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if (unlikely(___ret)) { \ |
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func(__VA_ARGS__); \ |
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__do_once_done(&___done, &___once_key, \ |
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&___flags); \ |
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} \ |
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} \ |
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___ret; \ |
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}) |
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#define get_random_once(buf, nbytes) \ |
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DO_ONCE(get_random_bytes, (buf), (nbytes)) |
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#define get_random_once_wait(buf, nbytes) \ |
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DO_ONCE(get_random_bytes_wait, (buf), (nbytes)) \ |
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#endif /* _LINUX_ONCE_H */
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