Incorporate feedback from bde and jilles regarding r265472 to dd(1).

* Don't use sysexits.h.  Just exit 1 on error and 0 otherwise.
* Don't sacrifice precision by converting the output of clock_gettime() to a
  double and then comparing the results.  Instead, subtract the values of
  the two clock_gettime() calls, then convert to double.
* Don't use CLOCK_MONOTONIC_PRECISE.  It's an unportable synonym for
  CLOCK_MONOTONIC.
* Use more appropriate names for some local variables.
* In the summary message, round elapsed time to the nearest microsecond.

Reported by:	bde, jilles
MFC after:	3 days
X-MFC-With:	265472

3 files changed, 12 insertions, 15 deletions

diff --git a/bin/dd/dd.c b/bin/dd/dd.c
index 6b4b4f0..8ae11a7 100644
--- a/bin/dd/dd.c
+++ b/bin/dd/dd.c
@@ -61,7 +61,6 @@ __FBSDID("$FreeBSD$");
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sysexits.h>
 #include <time.h>
 #include <unistd.h>
 
@@ -126,7 +125,6 @@ static void
 setup(void)
 {
 	u_int cnt;
-	struct timespec tv;
 
 	if (in.name == NULL) {
 		in.name = "stdin";
@@ -245,9 +243,8 @@ setup(void)
 		ctab = casetab;
 	}
 
-	if (clock_gettime(CLOCK_MONOTONIC_PRECISE, &tv))
-		err(EX_OSERR, "clock_gettime");
-	st.start = tv.tv_sec + tv.tv_nsec * 1.0e-9;
+	if (clock_gettime(CLOCK_MONOTONIC, &st.start))
+		err(1, "clock_gettime");
 }
 
 static void
diff --git a/bin/dd/dd.h b/bin/dd/dd.h
index d2fa410..a8b45e5 100644
--- a/bin/dd/dd.h
+++ b/bin/dd/dd.h
@@ -64,7 +64,7 @@ typedef struct {
 	uintmax_t	trunc;		/* # of truncated records */
 	uintmax_t	swab;		/* # of odd-length swab blocks */
 	uintmax_t	bytes;		/* # of bytes written */
-	double		start;		/* start time of dd */
+	struct timespec	start;		/* start time of dd */
 } STAT;
 
 /* Flags (in ddflags). */
diff --git a/bin/dd/misc.c b/bin/dd/misc.c
index 0d8da70..eb1227b 100644
--- a/bin/dd/misc.c
+++ b/bin/dd/misc.c
@@ -48,7 +48,6 @@ __FBSDID("$FreeBSD$");
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sysexits.h>
 #include <time.h>
 #include <unistd.h>
 
@@ -58,18 +57,19 @@ __FBSDID("$FreeBSD$");
 void
 summary(void)
 {
-	struct timespec tv, tv_res;
+	struct timespec end, ts_res;
 	double secs, res;
 
 	if (ddflags & C_NOINFO)
 		return;
 
-	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 (clock_gettime(CLOCK_MONOTONIC, &end))
+		err(1, "clock_gettime");
+	if (clock_getres(CLOCK_MONOTONIC, &ts_res))
+		err(1, "clock_getres");
+	secs = (end.tv_sec - st.start.tv_sec) + \
+	       (end.tv_nsec - st.start.tv_nsec) * 1e-9;
+	res = ts_res.tv_sec + ts_res.tv_nsec * 1e-9;
 	if (secs < res)
 		secs = res;
 	(void)fprintf(stderr,
@@ -83,7 +83,7 @@ summary(void)
 		     st.trunc, (st.trunc == 1) ? "block" : "blocks");
 	if (!(ddflags & C_NOXFER)) {
 		(void)fprintf(stderr,
-		    "%ju bytes transferred in %.9f secs (%.0f bytes/sec)\n",
+		    "%ju bytes transferred in %.6f secs (%.0f bytes/sec)\n",
 		    st.bytes, secs, st.bytes / secs);
 	}
 	need_summary = 0;