From 50590195351c11b218ad7edc50102a2e9eec7767 Mon Sep 17 00:00:00 2001
From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Thu, 15 Dec 2016 11:06:14 +0100
Subject: [PATCH] clientlog: randomize alignment of log timestamps

---
 clientlog.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/clientlog.c b/clientlog.c
index 1057326..0ace6d6 100644
--- a/clientlog.c
+++ b/clientlog.c
@@ -86,6 +86,10 @@ static unsigned int max_slots;
 #define TS_FRAC 4
 #define INVALID_TS 0
 
+/* Static offset included in conversion to the fixed-point timestamps to
+   randomise their alignment */
+static uint32_t ts_offset;
+
 /* Request rates are saved in the record as 8-bit scaled log2 values */
 #define RATE_SCALE 4
 #define MIN_RATE (-14 * RATE_SCALE)
@@ -134,6 +138,8 @@ static uint32_t total_ntp_drops;
 static uint32_t total_cmd_drops;
 static uint32_t total_record_drops;
 
+#define NSEC_PER_SEC 1000000000U
+
 /* ================================================== */
 
 static int expand_hashtable(void);
@@ -333,6 +339,9 @@ CLG_Initialise(void)
   records = NULL;
 
   expand_hashtable();
+
+  UTI_GetRandomBytes(&ts_offset, sizeof (ts_offset));
+  ts_offset %= NSEC_PER_SEC / (1U << TS_FRAC);
 }
 
 /* ================================================== */
@@ -353,6 +362,12 @@ get_ts_from_timespec(struct timespec *ts)
 {
   uint32_t sec = ts->tv_sec, nsec = ts->tv_nsec;
 
+  nsec += ts_offset;
+  if (nsec >= NSEC_PER_SEC) {
+    nsec -= NSEC_PER_SEC;
+    sec++;
+  }
+
   /* This is fast and accurate enough */
   return sec << TS_FRAC | (140740U * (nsec >> 15)) >> (32 - TS_FRAC);
 }