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Re: Broken autoconf mmap test

From: Bob Friesenhahn
Subject: Re: Broken autoconf mmap test
Date: Tue, 22 Mar 2011 17:25:18 -0500 (CDT)
User-agent: Alpine 2.01 (GSO 1266 2009-07-14)

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:

It was reported in

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.


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


in the build script. But it would be better to get a solution in autoconf itself.


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Bob Friesenhahn
GraphicsMagick Maintainer,

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