From 5b335920aa59a8a120914899b71a752acb29f1d9 Mon Sep 17 00:00:00 2001
From: "Yury V. Zaytsev" <yury@shurup.com>
Date: Tue, 30 Jul 2024 21:11:21 +0200
Subject: [PATCH] Ticket #3960: remove mmap support in file comparison

It's not working on AIX, but more importantly doesn't offer any benefits in
terms of speed, and we have a fallback anyways.

https://lists.gnu.org/archive/html/autoconf/2024-07/msg00006.html

Signed-off-by: Yury V. Zaytsev <yury@shurup.com>
---
 configure.ac                | 13 -------------
 doc/INSTALL                 |  6 ------
 maint/utils/travis-build.sh |  1 -
 src/filemanager/cmd.c       | 27 ++++-----------------------
 4 files changed, 4 insertions(+), 43 deletions(-)

diff --git a/configure.ac b/configure.ac
index e3d89eac4..5a9a4447f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -320,19 +320,6 @@ dnl replacing lstat with statlstat on sco makes it more portable between
 dnl sco clones
 AC_CHECK_FUNCS(statlstat)
 
-dnl Overriding mmap support.  This has to be before AC_FUNC_MMAP is used.
-dnl We use only part of the functionality of mmap, so on AIX,
-dnl it's possible to use mmap, even if it doesn't pass the autoconf test.
-AC_ARG_WITH([mmap],
-	AS_HELP_STRING([--with-mmap], [Use the mmap call @<:@yes if found@:>@]))
-if test x$with_mmap != xno; then
-    if test x$with_mmap = x; then
-	AC_FUNC_MMAP
-    else
-	AC_DEFINE(HAVE_MMAP, 1)
-    fi
-fi
-
 mc_GET_FS_INFO
 
 
diff --git a/doc/INSTALL b/doc/INSTALL
index 7e248df70..99302b5fc 100644
--- a/doc/INSTALL
+++ b/doc/INSTALL
@@ -103,12 +103,6 @@ incomplete, use `configure --help' to get the full list):
      building binaries for distribution purposes and may not work on
      some operating systems.
 
-`--with-mmap', `--without-mmap'
-     Force using or not using the mmap function.  It is currently used
-     in the internal viewer.  `--with-mmap' may be useful on some
-     versions of AIX where the `configure' script decides that mmap is
-     broken, but it's actually suitable for the internal viewer.
-
 `--with-subshell[=optional]', `--without-subshell' 
      The subshell support is by default turned on, you can disable
      this by using the --without-subshell option.  If you pass the
diff --git a/maint/utils/travis-build.sh b/maint/utils/travis-build.sh
index d7a00ee0f..92c5f9b75 100755
--- a/maint/utils/travis-build.sh
+++ b/maint/utils/travis-build.sh
@@ -92,7 +92,6 @@ mkdir -p build-all-disabled && pushd $_
     --disable-nls \
     --disable-vfs \
     --disable-background \
-    --without-mmap \
     --without-x \
     --without-gpm-mouse \
     --without-internal-edit \
diff --git a/src/filemanager/cmd.c b/src/filemanager/cmd.c
index b1e9a0d6b..496d62793 100644
--- a/src/filemanager/cmd.c
+++ b/src/filemanager/cmd.c
@@ -91,6 +91,7 @@
 #include "boxes.h"              /* cd_box() */
 #include "dir.h"
 #include "cd.h"
+#include "ioblksize.h"          /* IO_BUFSIZE */
 
 #include "cmd.h"                /* Our definitions */
 
@@ -189,27 +190,7 @@ compare_files (const vfs_path_t *vpath1, const vfs_path_t *vpath2, off_t size)
         file2 = open (vfs_path_as_str (vpath2), O_RDONLY);
         if (file2 >= 0)
         {
-#ifdef HAVE_MMAP
-            char *data1;
-
-            /* Ugly if jungle */
-            data1 = mmap (0, size, PROT_READ, MAP_FILE | MAP_PRIVATE, file1, 0);
-            if (data1 != (char *) -1)
-            {
-                char *data2;
-
-                data2 = mmap (0, size, PROT_READ, MAP_FILE | MAP_PRIVATE, file2, 0);
-                if (data2 != (char *) -1)
-                {
-                    rotate_dash (TRUE);
-                    result = memcmp (data1, data2, size);
-                    munmap (data2, size);
-                }
-                munmap (data1, size);
-            }
-#else
-            /* Don't have mmap() :( Even more ugly :) */
-            char buf1[BUFSIZ], buf2[BUFSIZ];
+            char buf1[IO_BUFSIZE], buf2[IO_BUFSIZE];
             ssize_t n1, n2;
 
             rotate_dash (TRUE);
@@ -222,12 +203,12 @@ compare_files (const vfs_path_t *vpath1, const vfs_path_t *vpath2, off_t size)
             }
             while (n1 == n2 && n1 == sizeof (buf1) && memcmp (buf1, buf2, sizeof (buf1)) == 0);
             result = (n1 != n2) || memcmp (buf1, buf2, n1);
-#endif /* !HAVE_MMAP */
+            rotate_dash (FALSE);
+
             close (file2);
         }
         close (file1);
     }
-    rotate_dash (FALSE);
 
     return result;
 }