From 46234253b9363894a254844a6550b4cc5f3edfe8 Mon Sep 17 00:00:00 2001 From: Hannes Frederic Sowa Date: Thu, 8 Oct 2015 01:20:35 +0200 Subject: net: move net_get_random_once to lib There's no good reason why users outside of networking should not be using this facility, f.e. for initializing their seeds. Therefore, make it accessible from there as get_random_once(). Signed-off-by: Hannes Frederic Sowa Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- include/linux/once.h | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) create mode 100644 include/linux/once.h (limited to 'include/linux/once.h') diff --git a/include/linux/once.h b/include/linux/once.h new file mode 100644 index 000000000000..2a83b538dd6a --- /dev/null +++ b/include/linux/once.h @@ -0,0 +1,24 @@ +#ifndef _LINUX_ONCE_H +#define _LINUX_ONCE_H + +#include +#include + +bool __get_random_once(void *buf, int nbytes, bool *done, + struct static_key *once_key); + +#define get_random_once(buf, nbytes) \ + ({ \ + bool ___ret = false; \ + static bool ___done = false; \ + static struct static_key ___once_key = \ + STATIC_KEY_INIT_TRUE; \ + if (static_key_true(&___once_key)) \ + ___ret = __get_random_once((buf), \ + (nbytes), \ + &___done, \ + &___once_key); \ + ___ret; \ + }) + +#endif /* _LINUX_ONCE_H */ -- cgit From c90aeb948222a7b3d3391d232ec4f50fd8322ad3 Mon Sep 17 00:00:00 2001 From: Hannes Frederic Sowa Date: Thu, 8 Oct 2015 01:20:36 +0200 Subject: once: make helper generic for calling functions once Make the get_random_once() helper generic enough, so that functions in general would only be called once, where one user of this is then net_get_random_once(). The only implementation specific call is to get_random_bytes(), all the rest of this *_once() facility would be duplicated among different subsystems otherwise. The new DO_ONCE() helper will be used by prandom() later on, but might also be useful for other scenarios/subsystems as well where a one-time initialization in often-called, possibly fast path code could occur. Signed-off-by: Hannes Frederic Sowa Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- include/linux/once.h | 61 ++++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 47 insertions(+), 14 deletions(-) (limited to 'include/linux/once.h') diff --git a/include/linux/once.h b/include/linux/once.h index 2a83b538dd6a..285f12cb40e6 100644 --- a/include/linux/once.h +++ b/include/linux/once.h @@ -4,21 +4,54 @@ #include #include -bool __get_random_once(void *buf, int nbytes, bool *done, - struct static_key *once_key); +bool __do_once_start(bool *done, unsigned long *flags); +void __do_once_done(bool *done, struct static_key *once_key, + unsigned long *flags); -#define get_random_once(buf, nbytes) \ - ({ \ - bool ___ret = false; \ - static bool ___done = false; \ - static struct static_key ___once_key = \ - STATIC_KEY_INIT_TRUE; \ - if (static_key_true(&___once_key)) \ - ___ret = __get_random_once((buf), \ - (nbytes), \ - &___done, \ - &___once_key); \ - ___ret; \ +/* 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 */ -- cgit