commit fc98fc71ea79f0e384f90814cb1a90c4e578bd9a Author: Aaron LI <a...@aaronly.me> Date: Thu Feb 14 21:38:21 2019 +0800
dd(1): Rework the time interval calculation 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 as the clock_id. That clock advances steadily, regardless of changes to the system clock. 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. Obtained-from: FreeBSD (revisions 265472,265698) Summary of changes: bin/dd/dd.c | 7 +++---- bin/dd/dd.h | 4 +++- bin/dd/extern.h | 1 + bin/dd/misc.c | 29 +++++++++++++++++++++++------ 4 files changed, 30 insertions(+), 11 deletions(-) http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/fc98fc71ea79f0e384f90814cb1a90c4e578bd9a -- DragonFly BSD source repository