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From: | Bob Friesenhahn |
Subject: | Re: mmap test failing on cygwin |
Date: | Sun, 20 Mar 2005 23:53:58 -0600 (CST) |
On Sun, 20 Mar 2005, Noah Misch wrote:
On Sun, Mar 20, 2005 at 10:59:13PM +0100, a.rburgers wrote:the autoconf test for mmap is failing for cygwin, although there is a functional mmap available on that platform.. This message gives a patch: http://lists.gnu.org/archive/html/autoconf-patches/2000-10/msg00241.htmlSummary: AC_FUNC_MMAP rejects the Cygwin mmap because MAP_FIXED on a malloc'ed region fails; rejecting it is bad because many programs that use mmap do not need that to work. Nonetheless, changing AC_FUNC_MMAP to help that majority, perhaps marginally, breaks programs relying on the check as it stands.
AC_FUNC_MMAP is working as designed. Mmap can be used for a great many things. Changing AC_FUNC_MMAP now would surely break programs which intend to test for its documented behavior.
I have attached a macro for a somewhat different mmap test which verifies that the system supports coherent mmap file I/O. This means that it is safe to update a file via both file descriptor and memory mapping without the content of the file getting confused. One of the systems rejected by this test is HP-UX (Cygwin passes). The test for a fixed mapping is not included in this macro.
Bob ====================================== Bob Friesenhahn address@hidden, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
mmap-fileio.m4
Description: mmap test for coherent I/O
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