[src/trunk]: src/usr.bin/kdump Print negative time offsets correctly. Provid...

[uwe <uwe%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/664250626af4
branches:  trunk
changeset: 826503:664250626af4
user:      uwe <uwe%NetBSD.org@localhost>
date:      Fri Sep 08 21:45:08 2017 +0000

description:
Print negative time offsets correctly.  Provide an exegetical quote
from riastradh@, slightly edited to fit the metre.

diffstat:

 usr.bin/kdump/kdump.c |  43 +++++++++++++++++++++++++++++++++++--------
 1 files changed, 35 insertions(+), 8 deletions(-)

diffs (91 lines):

diff -r 0a69d7813c7a -r 664250626af4 usr.bin/kdump/kdump.c
--- a/usr.bin/kdump/kdump.c     Fri Sep 08 21:09:29 2017 +0000
+++ b/usr.bin/kdump/kdump.c     Fri Sep 08 21:45:08 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kdump.c,v 1.127 2017/09/08 21:09:29 uwe Exp $  */
+/*     $NetBSD: kdump.c,v 1.128 2017/09/08 21:45:08 uwe Exp $  */
 
 /*-
  * Copyright (c) 1988, 1993
@@ -39,7 +39,7 @@
 #if 0
 static char sccsid[] = "@(#)kdump.c    8.4 (Berkeley) 4/28/95";
 #else
-__RCSID("$NetBSD: kdump.c,v 1.127 2017/09/08 21:09:29 uwe Exp $");
+__RCSID("$NetBSD: kdump.c,v 1.128 2017/09/08 21:45:08 uwe Exp $");
 #endif
 #endif /* not lint */
 
@@ -109,6 +109,7 @@
 
 static int     fread_tail(void *, size_t, size_t);
 static int     dumpheader(struct ktr_header *);
+static int     output_ts(const struct timespec *);
 static void    output_long(u_long, int);
 static void    ioctldecode(u_long);
 static void    ktrsyscall(struct ktr_syscall *);
@@ -399,8 +400,7 @@
                if (timestamp & TIMESTAMP_ABSOLUTE) {
                        temp.tv_sec = kth->ktr_ts.tv_sec;
                        temp.tv_nsec = kth->ktr_ts.tv_nsec;
-                       col += printf("%lld.%09ld ",
-                           (long long)temp.tv_sec, (long)temp.tv_nsec);
+                       col += output_ts(&temp);
                }
 
                if (timestamp & TIMESTAMP_ELAPSED) {
@@ -410,8 +410,7 @@
                                temp.tv_sec = temp.tv_nsec = 0;
                        } else
                                timespecsub(&kth->ktr_ts, &starttime, &temp);
-                       col += printf("%lld.%09ld ",
-                           (long long)temp.tv_sec, (long)temp.tv_nsec);
+                       col += output_ts(&temp);
                }
 
                if (timestamp & TIMESTAMP_RELATIVE) {
@@ -421,14 +420,42 @@
                                timespecsub(&kth->ktr_ts, &prevtime, &temp);
                        prevtime.tv_sec = kth->ktr_ts.tv_sec;
                        prevtime.tv_nsec = kth->ktr_ts.tv_nsec;
-                       col += printf("%lld.%09ld ",
-                           (long long)temp.tv_sec, (long)temp.tv_nsec);
+                       col += output_ts(&temp);
                }
        }
        col += printf("%-4s  ", type);
        return col;
 }
 
+static int
+output_ts(const struct timespec *ts)
+{
+       int col;
+
+       if (__predict_true(ts->tv_sec >= 0))
+           col = printf("%lld.%09ld ",
+                        (long long)ts->tv_sec, (long)ts->tv_nsec);
+       else {
+           /*
+            * The time represented by a timespec object ts is always
+            *
+            *   ts.tv_sec + ts.tv_nsec * 1e-9
+            *
+            * where ts.tv_sec may be negative but ts.tv_nsec is
+            * always in [0, 1e9).  So, for example, -1/4 second is
+            * represented by the struct timespec object
+            *
+            *   { .tv_sec = -1, .tv_nsec = 750000000 }
+            */
+           const struct timespec zero_ts = { 0, 0 };
+           struct timespec abs_ts;
+           timespecsub(&zero_ts, ts, &abs_ts);
+           col = printf("-%lld.%09ld ",
+                        (long long)abs_ts.tv_sec, (long)abs_ts.tv_nsec);
+       }
+       return col;
+}
+
 static void
 output_long(u_long it, int as_x)
 {