From d1d66eac15bffff6ed36d1d3e51b76048ae0b77b Mon Sep 17 00:00:00 2001
From: Alan Somers <asomers@FreeBSD.org>
Date: Tue, 6 May 2014 22:06:39 +0000
Subject: [PATCH] dd(1) uses gettimeofday(2) to compute the throughput
 statistics.  However, gettimeofday returns the system clock, which may jump
 forward or back, especially if NTP is in use.  If the time jumps backwards,
 then dd will see negative elapsed time, round it up to 1usec, and print an
 absurdly fast transfer rate.

The solution is to use clock_gettime(2) with CLOCK_MONOTONIC_PRECISE as the
clock_id.  That clock advances steadily, regardless of changes to the system
clock.

Reviewed by:	delphij
MFC after:	3 days
Sponsored by:	Spectra Logic
---
 bin/dd/dd.c   | 10 ++++++----
 bin/dd/misc.c | 22 ++++++++++++++--------
 2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/bin/dd/dd.c b/bin/dd/dd.c
index 7e5bd913a2d..8048b6a99d5 100644
--- a/bin/dd/dd.c
+++ b/bin/dd/dd.c
@@ -50,7 +50,6 @@ __FBSDID("$FreeBSD$");
 #include <sys/conf.h>
 #include <sys/disklabel.h>
 #include <sys/filio.h>
-#include <sys/time.h>
 
 #include <ctype.h>
 #include <err.h>
@@ -61,6 +60,8 @@ __FBSDID("$FreeBSD$");
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sysexits.h>
+#include <time.h>
 #include <unistd.h>
 
 #include "dd.h"
@@ -123,7 +124,7 @@ static void
 setup(void)
 {
 	u_int cnt;
-	struct timeval tv;
+	struct timespec tv;
 
 	if (in.name == NULL) {
 		in.name = "stdin";
@@ -240,8 +241,9 @@ setup(void)
 		ctab = casetab;
 	}
 
-	(void)gettimeofday(&tv, NULL);
-	st.start = tv.tv_sec + tv.tv_usec * 1e-6;
+	if (clock_gettime(CLOCK_MONOTONIC_PRECISE, &tv))
+		err(EX_OSERR, "clock_gettime");
+	st.start = tv.tv_sec + tv.tv_nsec * 1.0e-9;
 }
 
 static void
diff --git a/bin/dd/misc.c b/bin/dd/misc.c
index 61f843bf13a..0d8da700502 100644
--- a/bin/dd/misc.c
+++ b/bin/dd/misc.c
@@ -40,14 +40,16 @@ static char sccsid[] = "@(#)misc.c	8.3 (Berkeley) 4/2/94";
 __FBSDID("$FreeBSD$");
 
 #include <sys/types.h>
-#include <sys/time.h>
 
+#include <err.h>
 #include <errno.h>
 #include <inttypes.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sysexits.h>
+#include <time.h>
 #include <unistd.h>
 
 #include "dd.h"
@@ -56,16 +58,20 @@ __FBSDID("$FreeBSD$");
 void
 summary(void)
 {
-	struct timeval tv;
-	double secs;
+	struct timespec tv, tv_res;
+	double secs, res;
 
 	if (ddflags & C_NOINFO)
 		return;
 
-	(void)gettimeofday(&tv, NULL);
-	secs = tv.tv_sec + tv.tv_usec * 1e-6 - st.start;
-	if (secs < 1e-6)
-		secs = 1e-6;
+	if (clock_gettime(CLOCK_MONOTONIC_PRECISE, &tv))
+		err(EX_OSERR, "clock_gettime");
+	if (clock_getres(CLOCK_MONOTONIC_PRECISE, &tv_res))
+		err(EX_OSERR, "clock_getres");
+	secs = tv.tv_sec + tv.tv_nsec * 1.0e-9 - st.start;
+	res = tv_res.tv_sec + tv_res.tv_nsec * 1.0e-9;
+	if (secs < res)
+		secs = res;
 	(void)fprintf(stderr,
 	    "%ju+%ju records in\n%ju+%ju records out\n",
 	    st.in_full, st.in_part, st.out_full, st.out_part);
@@ -77,7 +83,7 @@ summary(void)
 		     st.trunc, (st.trunc == 1) ? "block" : "blocks");
 	if (!(ddflags & C_NOXFER)) {
 		(void)fprintf(stderr,
-		    "%ju bytes transferred in %.6f secs (%.0f bytes/sec)\n",
+		    "%ju bytes transferred in %.9f secs (%.0f bytes/sec)\n",
 		    st.bytes, secs, st.bytes / secs);
 	}
 	need_summary = 0;
-- 
2.45.0