cvs commit: src/sys/kern kern_tc.c

[Warner Losh]

imp         2003/06/25 14:23:51 PDT

  FreeBSD src repository

  Modified files:
    sys/kern             kern_tc.c 
  Log:
  Fix leap second processing by the kernel time keeping routines.
  Before, we would add/subtract the leap second when the system had been
  up for an even multiple of days, rather than at the end of the day, as
  a leap second is defined (at least wrt ntp).  We do this by
  calculating the notion of UTC earlier in the loop, and passing that to
  get it adjusted.  Any adjustments that ntp_update_second makes to this
  time are then transferred to boot time.  We can't pass it either the
  boot time or the uptime because their sum is what determines when a
  leap second is needed.  This code adds an extra assignment and two
  extra compare in the typical case, which is as cheap as I could made
  it.
  
  I have confirmed with this code the kernel time does the correct thing
  for both positive and negative leap seconds.  Since the ntp interface
  doesn't allow for +2 or -2, those cases can't be tested (and the folks
  in the know here say there will never be a +2s or -2s leap event, but
  rather two +1s or -1s leap events).
  
  There will very likely be no leap seconds for a while, given how the
  earth is speeding up and slowing down, so there will be plenty of time
  for this fix to propigate.  UT1-UTC is currently at "about -0.4s" and
  decrementing by .1s every 8 months or so.  6 * 8 is 48 months, or 4
  years.
  
  -stable has different code, but a similar bug that was introduced
  about the time of the last leap second, which is why nobody has
  noticed until now.
  
  MFC After: 3 weeks
  Reviewed by: phk
  
  "Furthermore, leap seconds must die." -- Cato the Elder
  
  Revision  Changes    Path
  1.151     +27 -6     src/sys/kern/kern_tc.c