https://bugs.gentoo.org/907474

From 87b95c17dc8611f9483b966d052eefc930f43927 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 5 Jun 2023 22:04:37 -0700
Subject: [PATCH] copy-file-range: support building for older kernels

* m4/copy-file-range.m4 (gl_FUNC_COPY_FILE_RANGE):
Remove static check, to support the dubious practice of
building for platforms that predate the build platform.
On working kernels this adds an extra syscall the first time
that copy_file_range is used.  Problem reported for Gentoo by
Sam James <https://bugs.gnu.org/63850>.
--- a/m4/copy-file-range.m4
+++ b/m4/copy-file-range.m4
@@ -39,21 +39,9 @@ AC_DEFUN([gl_FUNC_COPY_FILE_RANGE],
 
     case $host_os in
       linux*)
-        AC_CACHE_CHECK([whether copy_file_range is known to work],
-          [gl_cv_copy_file_range_known_to_work],
-          [AC_COMPILE_IFELSE(
-             [AC_LANG_PROGRAM(
-                [[#include <linux/version.h>
-                ]],
-                [[#if LINUX_VERSION_CODE < KERNEL_VERSION (5, 3, 0)
-                   #error "copy_file_range is buggy"
-                  #endif
-                ]])],
-             [gl_cv_copy_file_range_known_to_work=yes],
-             [gl_cv_copy_file_range_known_to_work=no])])
-        if test "$gl_cv_copy_file_range_known_to_work" = no; then
-          REPLACE_COPY_FILE_RANGE=1
-        fi;;
+        # See copy-file-range.c comment re pre-5.3 Linux kernel bugs.
+        # We should be able to remove this hack in 2025.
+        REPLACE_COPY_FILE_RANGE=1;;
     esac
   fi
 ])

--- a/configure
+++ b/configure
@@ -39903,42 +39903,9 @@ printf "%s\n" "#define HAVE_COPY_FILE_RANGE 1" >>confdefs.h
 
     case $host_os in
       linux*)
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether copy_file_range is known to work" >&5
-printf %s "checking whether copy_file_range is known to work... " >&6; }
-if test ${gl_cv_copy_file_range_known_to_work+y}
-then :
-  printf %s "(cached) " >&6
-else case e in #(
-  e) cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-#include <linux/version.h>
-
-int
-main (void)
-{
-#if LINUX_VERSION_CODE < KERNEL_VERSION (5, 3, 0)
-                   #error "copy_file_range is buggy"
-                  #endif
-
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"
-then :
-  gl_cv_copy_file_range_known_to_work=yes
-else case e in #(
-  e) gl_cv_copy_file_range_known_to_work=no ;;
-esac
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext ;;
-esac
-fi
-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $gl_cv_copy_file_range_known_to_work" >&5
-printf "%s\n" "$gl_cv_copy_file_range_known_to_work" >&6; }
-        if test "$gl_cv_copy_file_range_known_to_work" = no; then
-          REPLACE_COPY_FILE_RANGE=1
-        fi;;
+        # See copy-file-range.c comment re pre-5.3 Linux kernel bugs.
+        # We should be able to remove this hack in 2025.
+        REPLACE_COPY_FILE_RANGE=1;;
     esac
   fi