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[Bug libc/9690] glibc time functionality broken with kernel 2.6.26 and later


------- Additional Comments From samuel dot thibault at ens-lyon dot org  2009-05-07 22:59 -------
Subject: Re:  glibc time functionality broken with kernel 2.6.26 and later

johnstul at us dot ibm dot com, le Thu 07 May 2009 21:28:25 -0000, a écrit :
> > - the kernel now exposes nanoseconds instead of microseconds.  That's a
> > kernel ABI break.  It is announced via a STA_NANO flag in timex.status,
> > but still, old applications are broken when started under kernels >=
> > 2.6.26.  That's really a concern as it's not even easy to notice while
> > it can irritate users (unstable ntp time).
> 
> I'm not sure this is true. The kernel internally multiplies microseconds up to
> nanoseconds if the STA_NANO bit is not set. So old applications should behave
> properly.

Again, there are two issues:
- What the kernel takes as parameter. As you say, there is no problem
  indeed, if the application hasn't set the STA_NANO flag, the kernel
  converts properly.
- What the kernel returns. nanoseconds values are advertised by the
  kernel through the STA_NANO flag. But old applications didn't even
  know that flag, and thus can not know that these are nanosecond
  values.

> > As for the second issue, see Ulrich's comment: just define a new
> > version. See for instance the sched_setaffinity() function that has
> > changed its ABI (and API too actually).
> 
> Do we know if anyone is still working this? Roman's patch was seemingly ignored
> with no feedback.

There was: "define a new version to avoid breaking the ABI".

Samuel


-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=9690

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