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Date:	Thu,  8 Oct 2015 01:20:38 +0200
From:	Daniel Borkmann <>
Cc:,,, Daniel Borkmann <>
Subject: [PATCH net-next v2 4/5] random32: add prandom_init_once helper for own rngs

Add a prandom_init_once() facility that works on the rnd_state, so that
users that are keeping their own state independent from prandom_u32() can
initialize their taus113 per cpu states.

The motivation here is similar to net_get_random_once(): initialize the
state as late as possible in the hope that enough entropy has been
collected for the seeding. prandom_init_once() makes use of the recently
introduced prandom_seed_full_state() helper and is generic enough so that
it could also be used on fast-paths due to the DO_ONCE().

Signed-off-by: Daniel Borkmann <>
Acked-by: Hannes Frederic Sowa <>
 include/linux/random.h | 6 ++++++
 lib/random32.c         | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/random.h b/include/linux/random.h
index e651874..a75840c 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -7,6 +7,8 @@
 #define _LINUX_RANDOM_H
 #include <linux/list.h>
+#include <linux/once.h>
 #include <uapi/linux/random.h>
 struct random_ready_callback {
@@ -45,6 +47,10 @@ struct rnd_state {
 u32 prandom_u32_state(struct rnd_state *state);
 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
+void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);
+#define prandom_init_once(pcpu_state)			\
+	DO_ONCE(prandom_seed_full_state, (pcpu_state))
  * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
diff --git a/lib/random32.c b/lib/random32.c
index 36c09fb..1211191 100644
--- a/lib/random32.c
+++ b/lib/random32.c
@@ -238,7 +238,7 @@ static void __init __prandom_start_seed_timer(void)
-static void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
+void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
 	int i;

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