# copy-file-range.m4
dnl Copyright 2019-2023 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

AC_DEFUN([gl_FUNC_COPY_FILE_RANGE],
[
  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
  AC_REQUIRE([AC_CANONICAL_HOST])

  dnl Persuade glibc <unistd.h> to declare copy_file_range.
  AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])

  dnl Use AC_LINK_IFELSE, rather than AC_CHECK_FUNCS or a variant,
  dnl since we don't want AC_CHECK_FUNCS's checks for glibc stubs.
  dnl Programs that use copy_file_range must fall back on read+write
  dnl anyway, and there's little point to substituting the Gnulib stub
  dnl for a glibc stub.
  AC_CACHE_CHECK([for copy_file_range], [gl_cv_func_copy_file_range],
    [AC_LINK_IFELSE(
       [AC_LANG_PROGRAM(
          [[#include <unistd.h>
          ]],
          [[ssize_t (*func) (int, off_t *, int, off_t *, size_t, unsigned)
              = copy_file_range;
            return func (0, 0, 0, 0, 0, 0) & 127;
          ]])
       ],
       [gl_cv_func_copy_file_range=yes],
       [gl_cv_func_copy_file_range=no])
    ])

  if test "$gl_cv_func_copy_file_range" != yes; then
    HAVE_COPY_FILE_RANGE=0
  else
    AC_DEFINE([HAVE_COPY_FILE_RANGE], 1,
      [Define to 1 if the function copy_file_range exists.])

    case $host_os in
      linux*)
        # 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
])