[PATCH 1/5] random: add new clocksource entropy interface

@@ -129,6 +129,7 @@
  *                                unsigned int value);
  * 	void add_interrupt_randomness(int irq);
  * 	void add_disk_randomness(struct gendisk *disk);
+ * 	void add_clocksource_randomness(int delta);
  *
  * add_input_randomness() uses the input layer interrupt timing, as well as
  * the event type information from the hardware.

@@ -147,6 +148,12 @@
  * seek times do not make for good sources of entropy, as their seek
  * times are usually fairly consistent.
  *
+ * add_clocksource_randomness() uses time deltas between period reads
+ * of high-precision clocksources. The Linux kernel scheduler has no
+ * absolute guarantees of execution time, its best-effort, and we can
+ * be certain there will be entirely random variation in the actual
+ * deltas, at least at the nanosecond level for high-precision timers.
+ *
  * All of these routines try to estimate how many bits of randomness a
  * particular randomness source.  They do this by keeping track of the
  * first and second order deltas of the event timings.

@@ -722,6 +729,27 @@ void add_disk_randomness(struct gendisk *disk)
 }
 #endif
 
+void add_clocksource_randomness(int clock_delta)
+{
+	/* only mix in the low byte */
+	u8 mix = clock_delta & 0xff;
+
+	DEBUG_ENT("clock event %u\n", mix);
+
+	preempt_disable();
+	if (input_pool.entropy_count > trickle_thresh &&
+	    (__get_cpu_var(trickle_count)++ & 0xfff))
+		goto out;
+
+	mix_pool_bytes(&input_pool, &mix, sizeof(mix));
+	/* Only credit one bit per byte to be conservative */
+	credit_entropy_bits(&input_pool, sizeof(mix));
+
+out:
+	preempt_enable();
+}
+EXPORT_SYMBOL_GPL(add_clocksource_randomness);
+
 /*********************************************************************
  *
  * Entropy extraction routines

@@ -53,6 +53,7 @@ extern void rand_initialize_irq(int irq);
 extern void add_input_randomness(unsigned int type, unsigned int code,
 				 unsigned int value);
 extern void add_interrupt_randomness(int irq);
+extern void add_clocksource_randomness(int delta);
 
 extern void get_random_bytes(void *buf, int nbytes);
 void generate_random_uuid(unsigned char uuid_out[16]);