linux-stable/include/linux/once.h
David S. Miller 2a171788ba Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
Files removed in 'net-next' had their license header updated
in 'net'.  We take the remove from 'net-next'.

Signed-off-by: David S. Miller <davem@davemloft.net>
2017-11-04 09:26:51 +09:00

60 lines
1.8 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#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_true *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 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); \
} \
} \
___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)) \
#endif /* _LINUX_ONCE_H */