58 строки
1.7 KiB
C
58 строки
1.7 KiB
C
#ifndef _LINUX_ONCE_H
|
|
#define _LINUX_ONCE_H
|
|
|
|
#include <linux/types.h>
|
|
#include <linux/jump_label.h>
|
|
|
|
bool __do_once_start(bool *done, unsigned long *flags);
|
|
void __do_once_done(bool *done, struct static_key *once_key,
|
|
unsigned long *flags);
|
|
|
|
/* 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!
|
|
*
|
|
* Not 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 struct static_key ___once_key = STATIC_KEY_INIT_TRUE; \
|
|
if (static_key_true(&___once_key)) { \
|
|
unsigned long ___flags; \
|
|
___ret = __do_once_start(&___done, &___flags); \
|
|
if (unlikely(___ret)) { \
|
|
func(__VA_ARGS__); \
|
|
__do_once_done(&___done, &___once_key, \
|
|
&___flags); \
|
|
} \
|
|
} \
|
|
___ret; \
|
|
})
|
|
|
|
#define get_random_once(buf, nbytes) \
|
|
DO_ONCE(get_random_bytes, (buf), (nbytes))
|
|
|
|
#endif /* _LINUX_ONCE_H */
|