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c90aeb9482
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 <hannes@stressinduktion.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
58 lines
1.7 KiB
C
58 lines
1.7 KiB
C
#ifndef _LINUX_ONCE_H
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#define _LINUX_ONCE_H
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#include <linux/types.h>
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#include <linux/jump_label.h>
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bool __do_once_start(bool *done, unsigned long *flags);
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void __do_once_done(bool *done, struct static_key *once_key,
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unsigned long *flags);
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/* Call a function exactly once. The idea of DO_ONCE() is to perform
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* a function call such as initialization of random seeds, etc, only
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* once, where DO_ONCE() can live in the fast-path. After @func has
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* been called with the passed arguments, the static key will patch
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* out the condition into a nop. DO_ONCE() guarantees type safety of
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* arguments!
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*
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* Not that the following is not equivalent ...
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*
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* DO_ONCE(func, arg);
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* DO_ONCE(func, arg);
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*
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* ... to this version:
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*
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* void foo(void)
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* {
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* DO_ONCE(func, arg);
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* }
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*
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* foo();
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* foo();
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*
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* In case the one-time invocation could be triggered from multiple
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* places, then a common helper function must be defined, so that only
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* a single static key will be placed there!
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*/
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#define DO_ONCE(func, ...) \
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({ \
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bool ___ret = false; \
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static bool ___done = false; \
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static struct static_key ___once_key = STATIC_KEY_INIT_TRUE; \
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if (static_key_true(&___once_key)) { \
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unsigned long ___flags; \
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___ret = __do_once_start(&___done, &___flags); \
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if (unlikely(___ret)) { \
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func(__VA_ARGS__); \
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__do_once_done(&___done, &___once_key, \
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&___flags); \
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} \
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} \
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___ret; \
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})
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#define get_random_once(buf, nbytes) \
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DO_ONCE(get_random_bytes, (buf), (nbytes))
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#endif /* _LINUX_ONCE_H */
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