[bug #30517] Enable the user to ignore clock skew warnings partly/completely

[Kenneth Olwing]

URL:
  <http://savannah.gnu.org/bugs/?30517>

                 Summary: Enable the user to ignore clock skew warnings
partly/completely
                 Project: make
            Submitted by: ken1
            Submitted on: Thu 22 Jul 2010 09:03:54 AM GMT
                Severity: 3 - Normal
              Item Group: Enhancement
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
       Component Version: 3.81
        Operating System: Any
           Fixed Release: None
           Triage Status: None

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Details:

It's common to build things residing on another host through NFS. 

While the hosts should all use NTP to stay in sync, my experience has been
that make is far too sensitive for NTP in practice. We sometimes get messages
to the effect of "make: Warning: File `bar' has modification time 0.0035 s in
the future" and discussions to this effect has been had before through the
years but never been addressed.

While I really don't know if NTP is expected to reach this level of
synchronicity between hosts, this small drift seems to be a level I can live
with.

The one possibility to take care of this is .LOW_TIME_RESOLUTION, but the
main problem is that it would require me to change makefiles to use it. Most
of the time I really don't have that ooportunity. Actually, even if I did,
this mechanism seems flawed, as this aspect of a target isn't checked in the
section of remake.c where clock skew is warned for - so even if this target is
set, I still get clock skew messages.

I explored various ways to address this - e.g. forcing the
.LOW_TIME_RESOLUTION for all targets (but this didn't fly very well because of
the above), making the FILE_TIMESTAMP_HI_RES define become a runtime rather
than a compile time thing (but this proved far too complex with lots of
opportunities of creating subtle regressions).

In the end I settled for a short, sweet and very simple way: add a flag to
let the user indicate that clock skew warnings should be shut up, either
altogether (plain use of --ignore-clock-skew), or, more reasonable, by
indicating a level of clock skew that is acceptable (e.g.
--ignore-clock-skew=100 would allow timestamps up to 100 millisecs in the
future to be ignored). Without using the flag, everything is as before so it's
fully back compatible.

Attaching a patch for use in the root of a make-3.81 tree:

patch -p1 ignore-clock-skew.patch

ken1



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File Attachments:


-------------------------------------------------------
Date: Thu 22 Jul 2010 09:03:54 AM GMT  Name: ignore-clock-skew.patch  Size:
3kB   By: ken1

<http://savannah.gnu.org/bugs/download.php?file_id=21033>

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