/usr/share/aclocal/ax_have_epoll.m4 is in autoconf-archive 20160916-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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# http://www.gnu.org/software/autoconf-archive/ax_have_epoll.html
# ===========================================================================
#
# SYNOPSIS
#
# AX_HAVE_EPOLL([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
# AX_HAVE_EPOLL_PWAIT([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
#
# DESCRIPTION
#
# This macro determines whether the system supports the epoll I/O event
# interface. A neat usage example would be:
#
# AX_HAVE_EPOLL(
# [AX_CONFIG_FEATURE_ENABLE(epoll)],
# [AX_CONFIG_FEATURE_DISABLE(epoll)])
# AX_CONFIG_FEATURE(
# [epoll], [This platform supports epoll(7)],
# [HAVE_EPOLL], [This platform supports epoll(7).])
#
# The epoll interface was added to the Linux kernel in version 2.5.45, and
# the macro verifies that a kernel newer than this is installed. This
# check is somewhat unreliable if <linux/version.h> doesn't match the
# running kernel, but it is necessary regardless, because glibc comes with
# stubs for the epoll_create(), epoll_wait(), etc. that allow programs to
# compile and link even if the kernel is too old; the problem would then
# be detected only at runtime.
#
# Linux kernel version 2.6.19 adds the epoll_pwait() call in addition to
# epoll_wait(). The availability of that function can be tested with the
# second macro. Generally speaking, it is safe to assume that
# AX_HAVE_EPOLL would succeed if AX_HAVE_EPOLL_PWAIT has, but not the
# other way round.
#
# LICENSE
#
# Copyright (c) 2008 Peter Simons <simons@cryp.to>
#
# Copying and distribution of this file, with or without modification, are
# permitted in any medium without royalty provided the copyright notice
# and this notice are preserved. This file is offered as-is, without any
# warranty.
#serial 10
AC_DEFUN([AX_HAVE_EPOLL], [dnl
ax_have_epoll_cppflags="${CPPFLAGS}"
AC_CHECK_HEADER([linux/version.h], [CPPFLAGS="${CPPFLAGS} -DHAVE_LINUX_VERSION_H"])
AC_MSG_CHECKING([for Linux epoll(7) interface])
AC_CACHE_VAL([ax_cv_have_epoll], [dnl
AC_LINK_IFELSE([dnl
AC_LANG_PROGRAM([dnl
#include <sys/epoll.h>
#ifdef HAVE_LINUX_VERSION_H
# include <linux/version.h>
# if LINUX_VERSION_CODE < KERNEL_VERSION(2,5,45)
# error linux kernel version is too old to have epoll
# endif
#endif
], [dnl
int fd, rc;
struct epoll_event ev;
fd = epoll_create(128);
rc = epoll_wait(fd, &ev, 1, 0);])],
[ax_cv_have_epoll=yes],
[ax_cv_have_epoll=no])])
CPPFLAGS="${ax_have_epoll_cppflags}"
AS_IF([test "${ax_cv_have_epoll}" = "yes"],
[AC_MSG_RESULT([yes])
$1],[AC_MSG_RESULT([no])
$2])
])dnl
AC_DEFUN([AX_HAVE_EPOLL_PWAIT], [dnl
ax_have_epoll_cppflags="${CPPFLAGS}"
AC_CHECK_HEADER([linux/version.h],
[CPPFLAGS="${CPPFLAGS} -DHAVE_LINUX_VERSION_H"])
AC_MSG_CHECKING([for Linux epoll(7) interface with signals extension])
AC_CACHE_VAL([ax_cv_have_epoll_pwait], [dnl
AC_LINK_IFELSE([dnl
AC_LANG_PROGRAM([dnl
#ifdef HAVE_LINUX_VERSION_H
# include <linux/version.h>
# if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,19)
# error linux kernel version is too old to have epoll_pwait
# endif
#endif
#include <sys/epoll.h>
#include <signal.h>
], [dnl
int fd, rc;
struct epoll_event ev;
fd = epoll_create(128);
rc = epoll_wait(fd, &ev, 1, 0);
rc = epoll_pwait(fd, &ev, 1, 0, (sigset_t const *)(0));])],
[ax_cv_have_epoll_pwait=yes],
[ax_cv_have_epoll_pwait=no])])
CPPFLAGS="${ax_have_epoll_cppflags}"
AS_IF([test "${ax_cv_have_epoll_pwait}" = "yes"],
[AC_MSG_RESULT([yes])
$1],[AC_MSG_RESULT([no])
$2])
])dnl
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