lib/random32: export pseudo-random number generator for modules

This patch moves the definition of struct rnd_state and the inline
__seed() function to linux/random.h.  It renames the static __random32()
function to prandom32() and exports it for use in modules.

prandom32() is useful as a privately-seeded pseudo random number generator
that can give the same result every time it is initialized.

For FCoE FC-BB-6 VN2VN mode self-selected unique FC address generation, we
need an pseudo-random number generator seeded with the 64-bit world-wide
port name.  A truly random generator or one seeded with randomness won't
do because the same sequence of numbers should be generated each time we
boot or the link comes up.

A prandom32_seed() inline function is added to the header file.  It is
inlined not for speed, but so the function won't be expanded in the base
kernel, but only in the module that uses it.

Signed-off-by: Joe Eykholt <jeykholt@cisco.com>
Acked-by: Matt Mackall <mpm@selenic.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/include/linux/random.h b/include/linux/random.h
index 25d02fe..fb7ab9d 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -40,6 +40,10 @@ struct rand_pool_info {
 	__u32	buf[0];
 };
 
+struct rnd_state {
+	__u32 s1, s2, s3;
+};
+
 /* Exported functions */
 
 #ifdef __KERNEL__
@@ -74,6 +78,30 @@ unsigned long randomize_range(unsigned long start, unsigned long end, unsigned l
 u32 random32(void);
 void srandom32(u32 seed);
 
+u32 prandom32(struct rnd_state *);
+
+/*
+ * Handle minimum values for seeds
+ */
+static inline u32 __seed(u32 x, u32 m)
+{
+	return (x < m) ? x + m : x;
+}
+
+/**
+ * prandom32_seed - set seed for prandom32().
+ * @state: pointer to state structure to receive the seed.
+ * @seed: arbitrary 64-bit value to use as a seed.
+ */
+static inline void prandom32_seed(struct rnd_state *state, u64 seed)
+{
+	u32 i = (seed >> 32) ^ (seed << 10) ^ seed;
+
+	state->s1 = __seed(i, 1);
+	state->s2 = __seed(i, 7);
+	state->s3 = __seed(i, 15);
+}
+
 #endif /* __KERNEL___ */
 
 #endif /* _LINUX_RANDOM_H */