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(I'm so sorry!) Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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C
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#include <linux/types.h>#include <linux/jump_label.h>
/* Helpers used from arbitrary contexts. * Hard irqs are blocked, be cautious. */bool __do_once_start(bool *done, unsigned long *flags);void __do_once_done(bool *done, struct static_key_true *once_key, unsigned long *flags, struct module *mod);
/* Variant for process contexts only. */bool __do_once_sleepable_start(bool *done);void __do_once_sleepable_done(bool *done, struct static_key_true *once_key, struct module *mod);
/* Call a function exactly once. The idea of DO_ONCE() is to perform * a function call such as initialization of random seeds, etc, only * once, where DO_ONCE() can live in the fast-path. After @func has * been called with the passed arguments, the static key will patch * out the condition into a nop. DO_ONCE() guarantees type safety of * arguments! * * Note that the following is not equivalent ... * * DO_ONCE(func, arg); * DO_ONCE(func, arg); * * ... to this version: * * void foo(void) * { * DO_ONCE(func, arg); * } * * foo(); * foo(); * * In case the one-time invocation could be triggered from multiple * places, then a common helper function must be defined, so that only * a single static key will be placed there! */#define DO_ONCE(func, ...) \ ({ \ bool ___ret = false; \ static bool __section(".data..do_once") ___done = false; \ static DEFINE_STATIC_KEY_TRUE(___once_key); \ if (static_branch_unlikely(&___once_key)) { \ unsigned long ___flags; \ ___ret = __do_once_start(&___done, &___flags); \ if (unlikely(___ret)) { \ func(__VA_ARGS__); \ __do_once_done(&___done, &___once_key, \ &___flags, THIS_MODULE); \ } \ } \ ___ret; \ })
/* Variant of DO_ONCE() for process/sleepable contexts. */#define DO_ONCE_SLEEPABLE(func, ...) \ ({ \ bool ___ret = false; \ static bool __section(".data..do_once") ___done = false; \ static DEFINE_STATIC_KEY_TRUE(___once_key); \ if (static_branch_unlikely(&___once_key)) { \ ___ret = __do_once_sleepable_start(&___done); \ if (unlikely(___ret)) { \ func(__VA_ARGS__); \ __do_once_sleepable_done(&___done, &___once_key,\ THIS_MODULE); \ } \ } \ ___ret; \ })
#define get_random_once(buf, nbytes) \ DO_ONCE(get_random_bytes, (buf), (nbytes))
#define get_random_sleepable_once(buf, nbytes) \ DO_ONCE_SLEEPABLE(get_random_bytes, (buf), (nbytes))
#endif /* _LINUX_ONCE_H */