On Tue, 22 Mar 2011, Ken Brown wrote:
For a long time, the autoconf mmap test has failed on Cygwin even though
Cygwin has a working mmap. This was reported to bug-autoconf in November
2009, and a patch that fixed it for Cygwin was submitted by Eric Blake:
http://lists.gnu.org/archive/html/bug-autoconf/2009-11/msg00015.html
It was reported in
http://lists.gnu.org/archive/html/autoconf-patches/2009-11/msg00017.html
that the patch didn't help on HP/UX 11, which is another platform where the
test was failing. I can't find any follow-up to this in the archives of the
autoconf mailing lists.
The original intent of this macro was to only pass if MMAP I/O and
file I/O are coherent. In other words, programmed file I/O is
immediately reflected in already memory mapped file data (and
vice-versa). This is not the case for Windows and HP-UX. Given this,
Eric Blake's subsequent response to your email leaves me concerned.
In GraphicsMagick I use a somewhat modified version to test if mmap
works without requiring coherency.
Bob
Is there any chance of getting this bug fixed? Currently, the cygport tool
(which many Cygwin package maintainers use to build packages) works around it
by exporting
ac_cv_func_mmap_fixed_mapped=yes
in the build script. But it would be better to get a solution in autoconf
itself.
Ken
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--
Bob Friesenhahn
bfriesen@xxxxxxxxxxxxxxxxxxx, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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