svn commit: r337334 - head/lib/libc/sys

[Ian Lepore]

On Sat, 2018-08-04 at 16:39 -0600, Warner Losh wrote:
> On Sat, Aug 4, 2018 at 4:24 PM, Rodney W. Grimes <
> freebsd at pdx.rh.cn85.dnsmgr.net> wrote:
> 
> > 
> > > 
> > > Author: cem
> > > Date: Sat Aug  4 22:08:24 2018
> > > New Revision: 337334
> > > URL: https://svnweb.freebsd.org/changeset/base/337334
> > > 
> > > Log:
> > >   settimeofday(2): Remove stale note about timezone
> > > 
> > >   Contrary to the removed comment, the kernel does appear to use the
> > timezone
> > > 
> > >   argument of settimeofday.  The comment dates to the BSD4.4 import; I
> > assume it
> > > 
> > >   is just stale.
> > In what way is the kernel using TZ?   It shouldn't be.
> > Or is it using the TZ to adjust the passed in time to UTC/GMT,
> > which I would of thought is done before calling settimeofday.
> 
> Specifically, for compatibility, we store minutes west of UTC on
> settimeofday and we retrieve it for settimeofday. Otherwise it's 100%
> unused by anything else at all in the system. Well, technically, we use it
> for utc_offset, we don't really use that elsewhere (one can find references
> in utc_offset, but usually we set this via adjkerntz, which is actively
> used in the system). tz_minuteswest likely should just be removed, and the
> argument to settimzeofday should just be completely ignored.
> 

utc_offset is used by all RTC drivers, and by the convenience routines
that convert times to/from FAT filesystem format (which I assume are
used by FAT filesystem code, but I haven't checked that). So if the tz
info passed to settimeofday() ends up in utc_offset, how can we be sure
nobody is relying on that?

> One could test it with date -t, nothing does that today. That should be
> removed also. Likewise date -d.
> 
> So while hyper technically, one could use this, nobody does, nor has since
> between 4.3 and 4.4 when it was realized that storing the timezone in the
> kernel was a really stupid idea. That's what the language used in the man
> page that you removed was trying to say.
> 
> Warner
> 
> 
> > 
> > > 
> > > Modified:
> > >   head/lib/libc/sys/gettimeofday.2
> > > 
> > > Modified: head/lib/libc/sys/gettimeofday.2
> > > ============================================================
> > ==================
> > > 
> > > --- head/lib/libc/sys/gettimeofday.2  Sat Aug  4 21:57:17 2018
> > (r337333)
> > > 
> > > +++ head/lib/libc/sys/gettimeofday.2  Sat Aug  4 22:08:24 2018
> > (r337334)
> > > 
> > > @@ -28,7 +28,7 @@
> > >  .\"     @(#)gettimeofday.2   8.2 (Berkeley) 5/26/95
> > >  .\" $FreeBSD$
> > >  .\"
> > > -.Dd December 27, 2015
> > > +.Dd August 4, 2018
> > >  .Dt GETTIMEOFDAY 2
> > >  .Os
> > >  .Sh NAME
> > > @@ -44,11 +44,6 @@
> > >  .Ft int
> > >  .Fn settimeofday "const struct timeval *tp" "const struct timezone *tzp"
> > >  .Sh DESCRIPTION
> > > -.Bf -symbolic
> > > -Note: timezone is no longer used; this information is kept outside
> > > -the kernel.
> > > -.Ef
> > > -.Pp
> > >  The system's notion of the current Greenwich time and the current time
> > >  zone is obtained with the
> > >  .Fn gettimeofday
> > > 
> > > 
> > --
> > Rod Grimes
> > rgrimes at freebsd.org
> > 
> >