Current File : //usr/src/linux-headers-5.15.0-125-generic/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_slow_start(bool *done);
void __do_once_slow_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 ___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_SLOW(func, ...) \
({ \
bool ___ret = false; \
static bool __section(".data.once") ___done = false; \
static DEFINE_STATIC_KEY_TRUE(___once_key); \
if (static_branch_unlikely(&___once_key)) { \
___ret = __do_once_slow_start(&___done); \
if (unlikely(___ret)) { \
func(__VA_ARGS__); \
__do_once_slow_done(&___done, &___once_key, \
THIS_MODULE); \
} \
} \
___ret; \
})
#define get_random_once(buf, nbytes) \
DO_ONCE(get_random_bytes, (buf), (nbytes))
#define get_random_once_wait(buf, nbytes) \
DO_ONCE(get_random_bytes_wait, (buf), (nbytes)) \
#define get_random_slow_once(buf, nbytes) \
DO_ONCE_SLOW(get_random_bytes, (buf), (nbytes))
#endif /* _LINUX_ONCE_H */
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