Yup. Caught that.
Are there any security issues with changing environment variables?
On Mon, Feb 11, 2013 at 6:01 AM, Egger Clemens <[email protected]>wrote:
> regarding other places: when I developed that patch I found another
> similar use of mktime in the module ow_1923.c, however I didn't touch the
> code since I had no corresponding iButton for testing.
>
> Clemens
>
> > From: Paul Alfille [mailto:[email protected]]
> > Sent: Sunday, 10 February, 2013 1:15 AM
> > To: OWFS (One-wire file system) discussion and help
> > Subject: Re: [Owfs-developers] Patch - DS1921 Thermochron iButton -
> reading udate values depends on local time zone
> >
> > Thank you. The patch had been overlooked, but now is applied. I'm going
> to see if there are other places with the same error.
> > Paul
> >
> > On Fri, Feb 8, 2013 at 6:42 AM, Egger Clemens <[email protected]>
> wrote:
> > Hi Paul,
> >
> > any feedback for me regarding this patch?
> >
> > Best regards,
> > Clemens Egger
> >
> >
> > > -----Original Message-----
> > > From: Egger Clemens
> > > Sent: Wednesday, 23 January, 2013 1:16 PM
> > > To: OWFS Developer's list
> > > Subject: Patch - DS1921 Thermochron iButton - reading udate values
> > > depends on local time zone
> > >
> > > Hi,
> > >
> > > working with the DS1921 Thermochron iButton I noticed that, when
> writing a
> > > time value to clock/udate and reading it immediately afterwards, the
> > > returned value differs notably to the written value. This is dependent
> on the
> > > local time zone and whether it's daylight saving time or not. My
> environment
> > > variable TZ usually reads "Europe/Berlin". In the following example
> there's a
> > > difference of 3600 seconds i.e. 1 hour between the two values.
> > >
> > > $ ./owwrite -s 3000 21.D5542E000000/clock/udate 1352387000; ./owread -s
> > > 3000 21.D5542E000000/clock/udate
> > > 1352383400
> > >
> > > Looking at the source code, I discovered that the function mktime is
> used to
> > > convert a struct tm to time_t. However mktime uses the local time zone
> > > which explains the time shift.
> > >
> > > The following workaround makes the time shift disappear: just set the
> TZ
> > > environment variable to UTC when invoking the server.
> > > TZ=UTC ./owserver -u -p 3000
> > >
> > > There's a function timegm which is basically the opposite part to
> gmtime. The
> > > latter is already used in the code when writing a udate value to the
> iButton.
> > > In my opinion timegm would be more suitable than mktime. I developed a
> > > patch to fix this issue, see attachment.
> > >
> > > BTW: I already submitted this patch last year Nov 8 to this list, but
> I never got
> > > any feedback - just in case this sounds familiar.
> > >
> > > Best regards
> > > Clemens Egger
> >
>
>
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