prandom: introduce prandom_bytes() and prandom_bytes_state()

Add functions to get the requested number of pseudo-random bytes.

The difference from get_random_bytes() is that it generates pseudo-random
numbers by prandom_u32(). It doesn't consume the entropy pool, and the
sequence is reproducible if the same rnd_state is used. So it is suitable
for generating random bytes for testing.

Signed-off-by: Akinobu Mita <[e-mail]>
Cc: "Theodore Ts'o" <[e-mail]>
Cc: Artem Bityutskiy <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: David Woodhouse <[e-mail]>
Cc: Eilon Greenstein <[e-mail]>
Cc: David Laight <[e-mail]>
Cc: Michel Lespinasse <[e-mail]>
Cc: Robert Love <[e-mail]>
Cc: Valdis Kletnieks <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/random.h

···
 unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len);
 
 u32 prandom_u32(void);
+void prandom_bytes(void *buf, int nbytes);
 void prandom_seed(u32 seed);
 
 /*
···
 #define srandom32(seed) prandom_seed(seed)
 
 u32 prandom_u32_state(struct rnd_state *);
+void prandom_bytes_state(struct rnd_state *state, void *buf, int nbytes);
 
 /*
  * Handle minimum values for seeds

lib/random32.c

···
 }
 EXPORT_SYMBOL(prandom_u32);
 
+/*
+ *	prandom_bytes_state - get the requested number of pseudo-random bytes
+ *
+ *	@state: pointer to state structure holding seeded state.
+ *	@buf: where to copy the pseudo-random bytes to
+ *	@bytes: the requested number of bytes
+ *
+ *	This is used for pseudo-randomness with no outside seeding.
+ *	For more random results, use prandom_bytes().
+ */
+void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes)
+{
+	unsigned char *p = buf;
+	int i;
+
+	for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) {
+		u32 random = prandom_u32_state(state);
+		int j;
+
+		for (j = 0; j < sizeof(u32); j++) {
+			p[i + j] = random;
+			random >>= BITS_PER_BYTE;
+		}
+	}
+	if (i < bytes) {
+		u32 random = prandom_u32_state(state);
+
+		for (; i < bytes; i++) {
+			p[i] = random;
+			random >>= BITS_PER_BYTE;
+		}
+	}
+}
+EXPORT_SYMBOL(prandom_bytes_state);
+
+/**
+ *	prandom_bytes - get the requested number of pseudo-random bytes
+ *	@buf: where to copy the pseudo-random bytes to
+ *	@bytes: the requested number of bytes
+ */
+void prandom_bytes(void *buf, int bytes)
+{
+	struct rnd_state *state = &get_cpu_var(net_rand_state);
+
+	prandom_bytes_state(state, buf, bytes);
+	put_cpu_var(state);
+}
+EXPORT_SYMBOL(prandom_bytes);
+
 /**
  *	prandom_seed - add entropy to pseudo random number generator
  *	@seed: seed value