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Re: [PATCH 07/12] Use clock_gettime to implement ftime.
On 20/08/2019 10:21, Zack Weinberg wrote:
> ftime is an obsolete variation on gettimeofday, offering only
> millisecond time resolution; it was probably a system call in ooold
> versions of BSD Unix. For historic reasons, we had three
> implementations of it. These are all consolidated into time/ftime.c.
>
> Like gettimeofday, ftime tries to report the time zone, and using that
> information is always a bug. This patch dummies out the reported
> timezone information; the ‘timezone’ and ‘dstflag’ fields of the
> returned ‘struct timeb’ will always be zero.
>
> (There is an argument for turning this function into a compat symbol,
> and not installing sys/timeb.h anymore. Thoughts?)
It was removed in POSIX.1-2008 and moving it to a compat symbol it one less
symbol we would need to adapt to y2038. I think it is reasonable.
>
> * time/ftime.c (ftime): Replace implementation with the code
> formerly in sysdeps/unix/bsd/ftime.c, then change that code to use
> __clock_gettime instead of __gettimeofday. Always set the
> timezone and dstflag fields of the ‘timebuf’ argument to zero.
>
> * sysdeps/unix/bsd/ftime.c
> * sysdeps/unix/sysv/linux/ftime.c: Delete file.
LGTM with a nit below regarding clock_gettime (CLOCK_REALTIME).
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> sysdeps/unix/bsd/ftime.c | 40 ---------------------------------
> sysdeps/unix/sysv/linux/ftime.c | 3 ---
> time/ftime.c | 26 ++++++++++-----------
> 3 files changed, 12 insertions(+), 57 deletions(-)
> delete mode 100644 sysdeps/unix/bsd/ftime.c
> delete mode 100644 sysdeps/unix/sysv/linux/ftime.c
>
> diff --git a/sysdeps/unix/bsd/ftime.c b/sysdeps/unix/bsd/ftime.c
> deleted file mode 100644
> index 3a1c6e9b01..0000000000
> --- a/sysdeps/unix/bsd/ftime.c
> +++ /dev/null
> @@ -1,40 +0,0 @@
> -/* Copyright (C) 1994-2019 Free Software Foundation, Inc.
> - This file is part of the GNU C Library.
> -
> - The GNU C Library is free software; you can redistribute it and/or
> - modify it under the terms of the GNU Lesser General Public
> - License as published by the Free Software Foundation; either
> - version 2.1 of the License, or (at your option) any later version.
> -
> - The GNU C Library is distributed in the hope that it will be useful,
> - but WITHOUT ANY WARRANTY; without even the implied warranty of
> - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> - Lesser General Public License for more details.
> -
> - You should have received a copy of the GNU Lesser General Public
> - License along with the GNU C Library; if not, see
> - <http://www.gnu.org/licenses/>. */
> -
> -#include <sys/timeb.h>
> -#include <sys/time.h>
> -
> -int
> -ftime (struct timeb *timebuf)
> -{
> - struct timeval tv;
> - struct timezone tz;
> -
> - if (__gettimeofday (&tv, &tz) < 0)
> - return -1;
> -
> - timebuf->time = tv.tv_sec;
> - timebuf->millitm = (tv.tv_usec + 500) / 1000;
> - if (timebuf->millitm == 1000)
> - {
> - ++timebuf->time;
> - timebuf->millitm = 0;
> - }
> - timebuf->timezone = tz.tz_minuteswest;
> - timebuf->dstflag = tz.tz_dsttime;
> - return 0;
> -}
Ok.
> diff --git a/sysdeps/unix/sysv/linux/ftime.c b/sysdeps/unix/sysv/linux/ftime.c
> deleted file mode 100644
> index 5a5949f608..0000000000
> --- a/sysdeps/unix/sysv/linux/ftime.c
> +++ /dev/null
> @@ -1,3 +0,0 @@
> -/* Linux defines the ftime system call but doesn't actually implement
> - it. Use the BSD implementation. */
Ok.
> -#include <sysdeps/unix/bsd/ftime.c>
> diff --git a/time/ftime.c b/time/ftime.c
> index 6c2a256048..de8d043893 100644
> --- a/time/ftime.c
> +++ b/time/ftime.c
> @@ -15,27 +15,25 @@
> License along with the GNU C Library; if not, see
> <http://www.gnu.org/licenses/>. */
>
> -#include <errno.h>
> -#include <time.h>
> #include <sys/timeb.h>
> +#include <time.h>
>
> int
> ftime (struct timeb *timebuf)
> {
> - int save = errno;
> - struct tm tp;
> + struct timespec ts;
>
> - __set_errno (0);
> - if (time (&timebuf->time) == (time_t) -1 && errno != 0)
> + if (__clock_gettime (CLOCK_REALTIME, &ts) < 0)
> return -1;
I think we can assume CLOCK_REALTIME is always supported and &ts is always
valid, so we can skip the test here.
> - timebuf->millitm = 0;
> -
> - if (__localtime_r (&timebuf->time, &tp) == NULL)
> - return -1;
> -
> - timebuf->timezone = tp.tm_gmtoff / 60;
> - timebuf->dstflag = tp.tm_isdst;
>
> - __set_errno (save);
> + timebuf->time = ts.tv_sec;
> + timebuf->millitm = (ts.tv_nsec + 500000) / 1000000;
I think it is a fair assumption that kernel won't play foul here and give
us invalid tv_nsec.
> + if (timebuf->millitm == 1000)
> + {
> + ++timebuf->time;
> + timebuf->millitm = 0;
> + }
> + timebuf->timezone = 0;
> + timebuf->dstflag = 0;
> return 0;
> }
>