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.html
Summary: 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 bfriesen@xxxxxxxxxxxxxxxxxxx, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
# GM_FUNC_MMAP_FILEIO
# ------------
AC_DEFUN([GM_FUNC_MMAP_FILEIO],
[AC_CHECK_HEADERS(stdlib.h unistd.h)
AC_CHECK_FUNCS(getpagesize)
AC_CACHE_CHECK(for working mmap file i/o, gm_cv_func_mmap_fileio,
[AC_RUN_IFELSE([AC_LANG_SOURCE([AC_INCLUDES_DEFAULT]
[[/* malloc might have been renamed as rpl_malloc. */
#undef malloc
/*
This test is derived from GNU Autoconf's similar macro.
The purpose of this test is to verify that files may be memory
mapped, and that memory mapping and file I/O are coherent.
The test creates a test file, memory maps the file, updates
the file using the memory map, and then reads the file using
file I/O to verify that the file contains the updates.
*/
#include <fcntl.h>
#include <sys/mman.h>
#if !STDC_HEADERS && !HAVE_STDLIB_H
char *malloc ();
#endif
/* This mess was copied from the GNU getpagesize.h. */
#if !HAVE_GETPAGESIZE
/* Assume that all systems that can run configure have sys/param.h. */
# if !HAVE_SYS_PARAM_H
# define HAVE_SYS_PARAM_H 1
# endif
# ifdef _SC_PAGESIZE
# define getpagesize() sysconf(_SC_PAGESIZE)
# else /* no _SC_PAGESIZE */
# if HAVE_SYS_PARAM_H
# include <sys/param.h>
# ifdef EXEC_PAGESIZE
# define getpagesize() EXEC_PAGESIZE
# else /* no EXEC_PAGESIZE */
# ifdef NBPG
# define getpagesize() NBPG * CLSIZE
# ifndef CLSIZE
# define CLSIZE 1
# endif /* no CLSIZE */
# else /* no NBPG */
# ifdef NBPC
# define getpagesize() NBPC
# else /* no NBPC */
# ifdef PAGESIZE
# define getpagesize() PAGESIZE
# endif /* PAGESIZE */
# endif /* no NBPC */
# endif /* no NBPG */
# endif /* no EXEC_PAGESIZE */
# else /* no HAVE_SYS_PARAM_H */
# define getpagesize() 8192 /* punt totally */
# endif /* no HAVE_SYS_PARAM_H */
# endif /* no _SC_PAGESIZE */
#endif /* no HAVE_GETPAGESIZE */
int
main ()
{
char *data, *data2, *data3;
int i, pagesize;
int fd;
pagesize = getpagesize ();
/* First, make a file with some known garbage in it. */
data = (char *) malloc (pagesize);
if (!data)
exit (1);
for (i = 0; i < pagesize; ++i)
*(data + i) = rand ();
umask (0);
fd = creat ("conftest.mmap", 0600);
if (fd < 0)
exit (1);
if (write (fd, data, pagesize) != pagesize)
exit (1);
close (fd);
/* Mmap the file as read/write/shared and verify that we see the
same garbage. */
fd = open ("conftest.mmap", O_RDWR);
if (fd < 0)
exit (1);
data2 = mmap (0, pagesize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0L);
if (data2 == 0)
exit (1);
for (i = 0; i < pagesize; ++i)
if (*(data + i) != *(data2 + i))
exit (1);
/* Finally, make sure that changes to the mapped area
percolate back to the file as seen by read(). */
for (i = 0; i < pagesize; ++i)
*(data2 + i) = *(data2 + i) + 1;
data3 = (char *) malloc (pagesize);
if (!data3)
exit (1);
if (read (fd, data3, pagesize) != pagesize)
exit (1);
for (i = 0; i < pagesize; ++i)
if (*(data2 + i) != *(data3 + i))
exit (1);
close (fd);
exit (0);
}]])],
[gm_cv_func_mmap_fileio=yes],
[gm_cv_func_mmap_fileio=no],
[gm_cv_func_mmap_fileio=no])])
if test $gm_cv_func_mmap_fileio = yes; then
AC_DEFINE(HAVE_MMAP_FILEIO, 1,
[Define to 1 if you have a `mmap' system call which handles coherent file I/O.])
fi
rm -f conftest.mmap
])# GM_FUNC_MMAP_FILEIO
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