Building 2.3.4 from the tarball, 
#define HAVE_FDATASYNC 1
appears in the pyconfig.h file, and
the build of 'posixmodule' fails with
undefined symbol _fdatasync

Workaround is to delete the line
and proceed, of course, but I've
never seen this before when building
under cygwin.

There is no 'fdatasync' mentioned
in any /usr/include/*.h or /usr/local/include/*.h

The cygwin installation is kind of a mongrel
(4 or 5 upgrades since install, some selective)
This is the ID string from the built python:

Python 2.3.4 (#2, Jul  4 2004, 22:10:22)
[GCC 3.3.1 (cygming special)] on cygwin

Let me know of any details of the cygwin install
which might be useful.

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That's odd.  Why does configure think you have fdatasync?  Maybe 
config.log will help...

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looked into config.log and 'configure' itself.. the compile
for fdatasync succeeded, but the script does not attempt
to link it.  gcc -E  led me to the following 
chunk of /usr/include/sys/unistd.h:

(not inside any #ifdefs, as far as I can tell)

int     _EXFUN(fdatasync, (int __fd));


So it's declared in the header, but it's not in the
library. This symbol is defined in libc.a on a RH8.0
system, I can't find it anywhere on the cygwin system.
 

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Well, I guess that's an arguable bug in cygwin, but if you want to 
supply a patch that modifies configure to do the linking test too, 
I'll at least think about applying it :-)

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Jason, do you know what the deal is with cygwin?

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nnorwitz> Jason, do you know what the deal is with cygwin?

AFAICT, Greg's Cygwin setup seems suspect.  Actually, he
alluded to this fact in the following:

gregsmith> The cygwin installation is kind of a mongrel...

On my Cygwin setup (i.e., 1.5.10-3), I have the following:

/usr/include/sys/unistd.h:
    #ifndef __CYGWIN__
    int     _EXFUN(fdatasync, (int __fd));
    #endif

pyconfig.h:

    /* Define if you have the 'fdatasync' function. */
    /* #undef HAVE_FDATASYNC */

Additionally, the official Cygwin Python package built
cleanly.

Greg, what version of Cygwin are you using? If not 1.5.10-3,
then please upgrade and try again. If so, then your setup
seems to be corrupted. Try reinstalling. Does it work any
better now?

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There has been no follow-up from Greg in a month.
OK to close?

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Your wish is my command. :-)  Closing as invalid, since this
seems more a cygwin setup problem.  Greg can re-open if he
disagrees.

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Fine with me .
Sorry about being out of touch for so long - I had to
beef up my mail filtering due to spam, and as a
side-effect the sourceforge traffic no longer shows up
directly in front of me... 

Anyway, it seems pretty clear there's an anomaly with
my cygwin (which shows 1.5.7-1); if no-one else has
it then clearly there's no point in messing with the
python install to fix it.

I've had bad experiences with things breaking when
I upgrade cygwin, so I'm squiffy about doing it again,
maybe it's time for a 'scorched earth mode' upgrade.

Thanks.