linux/include/linux/once.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_ONCE_H
#define _LINUX_ONCE_H

#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, ...) …

/* Variant of DO_ONCE() for process/sleepable contexts. */
#define DO_ONCE_SLEEPABLE(func, ...) …

#define get_random_once(buf, nbytes) …

#define get_random_sleepable_once(buf, nbytes) …

#endif /* _LINUX_ONCE_H */