netsnmp: handle libnl dependency properly

libnl3 include path was hardcoded in the configure script,
causing the following gcc warning:

WARNING: unsafe header/library path used in cross-compilation:
'/usr/include/libnl3'

Let's apply an upstream patch that addresses the issue: now
pkg-config is used to detect libnl include path.

Also:
- add optional libnl build dependency;
- enable libnl support only when libnl package is selected.

Signed-off-by: Julien Floret <julien.floret@6wind.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/netsnmp/0001-configure-Eliminate-the-hard-coded-libnl-3-include-p.patch

@@ -0,0 +1,300 @@
+From 57d6c3d36045aab8957ffeb7324728bf17faf8bd Mon Sep 17 00:00:00 2001
+From: Bart Van Assche <bvanassche@acm.org>
+Date: Mon, 2 Feb 2015 20:31:29 +0100
+Subject: [PATCH] configure: Eliminate the hard-coded libnl-3 include path
+
+See also commit 3dde41998625fe0e24119a2e1f4509ba3ba2fd9a.
+
+(cherry picked from commit 852dcd644cfe4cfc7177649eaec163d6221f2be1)
+
+Original commit included modifications to configure script.
+Do not keep these modifications, since they caused lots of conflicts, and
+configure script is meant to be automatically generated.
+
+Signed-off-by: Julien Floret <julien.floret@6wind.com>
+
+Conflicts:
+	configure
+---
+ aclocal.m4                  |   1 +
+ configure.d/config_os_libs2 |  30 ++++++-
+ m4/pkg.m4                   | 214 ++++++++++++++++++++++++++++++++++++++++++++
+ 3 files changed, 243 insertions(+), 2 deletions(-)
+ create mode 100644 m4/pkg.m4
+
+diff --git a/aclocal.m4 b/aclocal.m4
+index cd80c7486f2f..45e3608ed480 100644
+--- a/aclocal.m4
++++ b/aclocal.m4
+@@ -22,3 +22,4 @@ m4_include([m4/ltversion.m4])
+ m4_include([m4/lt~obsolete.m4])
+ m4_include([m4/netsnmp_arg.m4])
+ m4_include([m4/netsnmp_search_libs.m4])
++m4_include([m4/pkg.m4])
+diff --git a/configure.d/config_os_libs2 b/configure.d/config_os_libs2
+index 47491e24ce0a..10bd414b879e 100644
+--- a/configure.d/config_os_libs2
++++ b/configure.d/config_os_libs2
+@@ -225,11 +225,37 @@ fi
+ if test "x$with_nl" != "xno"; then
+     case $target_os in
+     linux*) # Check for libnl (linux)
++        # The test below verifies whether the libnl-3 package been installed.
++        # This test works as follows:
++        # - If pkg-config was not installed at the time autogen.sh was run,
++        #   the definition of the PKG_CHECK_EXISTS() macro will not be found by
++        #   autogen.sh. Augogen.sh will generate a configure script that prints
++        #   a warning about pkg-config and proceeds as if libnl-3 has not been
++        #   installed.
++        # - If pkg-config was installed at the time autogen.sh was run,
++        #   the generated configure script will try to detect the presence of
++        #   the libnl-3 library by looking up compile and linker flags in the
++        #   file called libnl-3.pc.
++        # - pkg-config settings can be overridden via the configure variables
++        #   LIBNL3_CFLAGS and LIBNL3_LIBS (added by the pkg-config m4 macro's to
++        #   the configure script -- see also ./configure --help).
++        # - The LIBNL3_CFLAGS and LIBNL3_LIBS configure variables can be used
++        #   even if the pkg-config executable is not present on the system on
++        #   which the configure script is run.
++        ifdef(
++          [PKG_CHECK_EXISTS],
++          [PKG_CHECK_EXISTS([libnl-3.0],
++            [PKG_CHECK_MODULES([LIBNL3], [libnl-3.0])])
++          ],
++          AC_MSG_WARN([pkg-config has not been installed or is too old.])
++          AC_MSG_WARN([Detection of libnl-3.0 will be skipped.])
++        )
++
+         netsnmp_save_CPPFLAGS="$CPPFLAGS"
+-        CPPFLAGS="-I/usr/include/libnl3 $CPPFLAGS"
++        CPPFLAGS="${LIBNL3_CFLAGS} $CPPFLAGS"
+         NETSNMP_SEARCH_LIBS(nl_connect, nl-3,
+             [AC_CHECK_HEADERS(netlink/netlink.h)
+-            EXTERNAL_MIBGROUP_INCLUDES="$EXTERNAL_MIBGROUP_INCLUDES -I/usr/include/libnl3"],
++            EXTERNAL_MIBGROUP_INCLUDES="$EXTERNAL_MIBGROUP_INCLUDES ${LIBNL3_CFLAGS}"],
+             [CPPFLAGS="$netsnmp_save_CPPFLAGS"], [], [], [LMIBLIBS])
+         if test "x$ac_cv_header_netlink_netlink_h" != xyes; then
+             NETSNMP_SEARCH_LIBS(nl_connect, nl, [
+diff --git a/m4/pkg.m4 b/m4/pkg.m4
+new file mode 100644
+index 000000000000..c5b26b52e6cd
+--- /dev/null
++++ b/m4/pkg.m4
+@@ -0,0 +1,214 @@
++# pkg.m4 - Macros to locate and utilise pkg-config.            -*- Autoconf -*-
++# serial 1 (pkg-config-0.24)
++# 
++# Copyright © 2004 Scott James Remnant <scott@netsplit.com>.
++#
++# This program is free software; you can redistribute it and/or modify
++# it under the terms of the GNU General Public License as published by
++# the Free Software Foundation; either version 2 of the License, or
++# (at your option) any later version.
++#
++# This program is distributed in the hope that it will be useful, but
++# WITHOUT ANY WARRANTY; without even the implied warranty of
++# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
++# General Public License for more details.
++#
++# You should have received a copy of the GNU General Public License
++# along with this program; if not, write to the Free Software
++# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
++#
++# As a special exception to the GNU General Public License, if you
++# distribute this file as part of a program that contains a
++# configuration script generated by Autoconf, you may include it under
++# the same distribution terms that you use for the rest of that program.
++
++# PKG_PROG_PKG_CONFIG([MIN-VERSION])
++# ----------------------------------
++AC_DEFUN([PKG_PROG_PKG_CONFIG],
++[m4_pattern_forbid([^_?PKG_[A-Z_]+$])
++m4_pattern_allow([^PKG_CONFIG(_(PATH|LIBDIR|SYSROOT_DIR|ALLOW_SYSTEM_(CFLAGS|LIBS)))?$])
++m4_pattern_allow([^PKG_CONFIG_(DISABLE_UNINSTALLED|TOP_BUILD_DIR|DEBUG_SPEW)$])
++AC_ARG_VAR([PKG_CONFIG], [path to pkg-config utility])
++AC_ARG_VAR([PKG_CONFIG_PATH], [directories to add to pkg-config's search path])
++AC_ARG_VAR([PKG_CONFIG_LIBDIR], [path overriding pkg-config's built-in search path])
++
++if test "x$ac_cv_env_PKG_CONFIG_set" != "xset"; then
++	AC_PATH_TOOL([PKG_CONFIG], [pkg-config])
++fi
++if test -n "$PKG_CONFIG"; then
++	_pkg_min_version=m4_default([$1], [0.9.0])
++	AC_MSG_CHECKING([pkg-config is at least version $_pkg_min_version])
++	if $PKG_CONFIG --atleast-pkgconfig-version $_pkg_min_version; then
++		AC_MSG_RESULT([yes])
++	else
++		AC_MSG_RESULT([no])
++		PKG_CONFIG=""
++	fi
++fi[]dnl
++])# PKG_PROG_PKG_CONFIG
++
++# PKG_CHECK_EXISTS(MODULES, [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
++#
++# Check to see whether a particular set of modules exists.  Similar
++# to PKG_CHECK_MODULES(), but does not set variables or print errors.
++#
++# Please remember that m4 expands AC_REQUIRE([PKG_PROG_PKG_CONFIG])
++# only at the first occurence in configure.ac, so if the first place
++# it's called might be skipped (such as if it is within an "if", you
++# have to call PKG_CHECK_EXISTS manually
++# --------------------------------------------------------------
++AC_DEFUN([PKG_CHECK_EXISTS],
++[AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
++if test -n "$PKG_CONFIG" && \
++    AC_RUN_LOG([$PKG_CONFIG --exists --print-errors "$1"]); then
++  m4_default([$2], [:])
++m4_ifvaln([$3], [else
++  $3])dnl
++fi])
++
++# _PKG_CONFIG([VARIABLE], [COMMAND], [MODULES])
++# ---------------------------------------------
++m4_define([_PKG_CONFIG],
++[if test -n "$$1"; then
++    pkg_cv_[]$1="$$1"
++ elif test -n "$PKG_CONFIG"; then
++    PKG_CHECK_EXISTS([$3],
++                     [pkg_cv_[]$1=`$PKG_CONFIG --[]$2 "$3" 2>/dev/null`
++		      test "x$?" != "x0" && pkg_failed=yes ],
++		     [pkg_failed=yes])
++ else
++    pkg_failed=untried
++fi[]dnl
++])# _PKG_CONFIG
++
++# _PKG_SHORT_ERRORS_SUPPORTED
++# -----------------------------
++AC_DEFUN([_PKG_SHORT_ERRORS_SUPPORTED],
++[AC_REQUIRE([PKG_PROG_PKG_CONFIG])
++if $PKG_CONFIG --atleast-pkgconfig-version 0.20; then
++        _pkg_short_errors_supported=yes
++else
++        _pkg_short_errors_supported=no
++fi[]dnl
++])# _PKG_SHORT_ERRORS_SUPPORTED
++
++
++# PKG_CHECK_MODULES(VARIABLE-PREFIX, MODULES, [ACTION-IF-FOUND],
++# [ACTION-IF-NOT-FOUND])
++#
++#
++# Note that if there is a possibility the first call to
++# PKG_CHECK_MODULES might not happen, you should be sure to include an
++# explicit call to PKG_PROG_PKG_CONFIG in your configure.ac
++#
++#
++# --------------------------------------------------------------
++AC_DEFUN([PKG_CHECK_MODULES],
++[AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
++AC_ARG_VAR([$1][_CFLAGS], [C compiler flags for $1, overriding pkg-config])dnl
++AC_ARG_VAR([$1][_LIBS], [linker flags for $1, overriding pkg-config])dnl
++
++pkg_failed=no
++AC_MSG_CHECKING([for $1])
++
++_PKG_CONFIG([$1][_CFLAGS], [cflags], [$2])
++_PKG_CONFIG([$1][_LIBS], [libs], [$2])
++
++m4_define([_PKG_TEXT], [Alternatively, you may set the environment variables $1[]_CFLAGS
++and $1[]_LIBS to avoid the need to call pkg-config.
++See the pkg-config man page for more details.])
++
++if test $pkg_failed = yes; then
++   	AC_MSG_RESULT([no])
++        _PKG_SHORT_ERRORS_SUPPORTED
++        if test $_pkg_short_errors_supported = yes; then
++	        $1[]_PKG_ERRORS=`$PKG_CONFIG --short-errors --print-errors --cflags --libs "$2" 2>&1`
++        else 
++	        $1[]_PKG_ERRORS=`$PKG_CONFIG --print-errors --cflags --libs "$2" 2>&1`
++        fi
++	# Put the nasty error message in config.log where it belongs
++	echo "$$1[]_PKG_ERRORS" >&AS_MESSAGE_LOG_FD
++
++	m4_default([$4], [AC_MSG_ERROR(
++[Package requirements ($2) were not met:
++
++$$1_PKG_ERRORS
++
++Consider adjusting the PKG_CONFIG_PATH environment variable if you
++installed software in a non-standard prefix.
++
++_PKG_TEXT])[]dnl
++        ])
++elif test $pkg_failed = untried; then
++     	AC_MSG_RESULT([no])
++	m4_default([$4], [AC_MSG_FAILURE(
++[The pkg-config script could not be found or is too old.  Make sure it
++is in your PATH or set the PKG_CONFIG environment variable to the full
++path to pkg-config.
++
++_PKG_TEXT
++
++To get pkg-config, see <http://pkg-config.freedesktop.org/>.])[]dnl
++        ])
++else
++	$1[]_CFLAGS=$pkg_cv_[]$1[]_CFLAGS
++	$1[]_LIBS=$pkg_cv_[]$1[]_LIBS
++        AC_MSG_RESULT([yes])
++	$3
++fi[]dnl
++])# PKG_CHECK_MODULES
++
++
++# PKG_INSTALLDIR(DIRECTORY)
++# -------------------------
++# Substitutes the variable pkgconfigdir as the location where a module
++# should install pkg-config .pc files. By default the directory is
++# $libdir/pkgconfig, but the default can be changed by passing
++# DIRECTORY. The user can override through the --with-pkgconfigdir
++# parameter.
++AC_DEFUN([PKG_INSTALLDIR],
++[m4_pushdef([pkg_default], [m4_default([$1], ['${libdir}/pkgconfig'])])
++m4_pushdef([pkg_description],
++    [pkg-config installation directory @<:@]pkg_default[@:>@])
++AC_ARG_WITH([pkgconfigdir],
++    [AS_HELP_STRING([--with-pkgconfigdir], pkg_description)],,
++    [with_pkgconfigdir=]pkg_default)
++AC_SUBST([pkgconfigdir], [$with_pkgconfigdir])
++m4_popdef([pkg_default])
++m4_popdef([pkg_description])
++]) dnl PKG_INSTALLDIR
++
++
++# PKG_NOARCH_INSTALLDIR(DIRECTORY)
++# -------------------------
++# Substitutes the variable noarch_pkgconfigdir as the location where a
++# module should install arch-independent pkg-config .pc files. By
++# default the directory is $datadir/pkgconfig, but the default can be
++# changed by passing DIRECTORY. The user can override through the
++# --with-noarch-pkgconfigdir parameter.
++AC_DEFUN([PKG_NOARCH_INSTALLDIR],
++[m4_pushdef([pkg_default], [m4_default([$1], ['${datadir}/pkgconfig'])])
++m4_pushdef([pkg_description],
++    [pkg-config arch-independent installation directory @<:@]pkg_default[@:>@])
++AC_ARG_WITH([noarch-pkgconfigdir],
++    [AS_HELP_STRING([--with-noarch-pkgconfigdir], pkg_description)],,
++    [with_noarch_pkgconfigdir=]pkg_default)
++AC_SUBST([noarch_pkgconfigdir], [$with_noarch_pkgconfigdir])
++m4_popdef([pkg_default])
++m4_popdef([pkg_description])
++]) dnl PKG_NOARCH_INSTALLDIR
++
++
++# PKG_CHECK_VAR(VARIABLE, MODULE, CONFIG-VARIABLE,
++# [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
++# -------------------------------------------
++# Retrieves the value of the pkg-config variable for the given module.
++AC_DEFUN([PKG_CHECK_VAR],
++[AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
++AC_ARG_VAR([$1], [value of $3 for $2, overriding pkg-config])dnl
++
++_PKG_CONFIG([$1], [variable="][$3]["], [$2])
++AS_VAR_COPY([$1], [pkg_cv_][$1])
++
++AS_VAR_IF([$1], [""], [$5], [$4])dnl
++])# PKG_CHECK_VAR
+-- 
+2.1.0
+

package/netsnmp/netsnmp.mk

@@ -36,6 +36,7 @@ NETSNMP_INSTALL_STAGING_OPTS = DESTDIR=$(STAGING_DIR) LIB_LDCONFIG_CMD=true inst
 NETSNMP_INSTALL_TARGET_OPTS = DESTDIR=$(TARGET_DIR) LIB_LDCONFIG_CMD=true install
 NETSNMP_MAKE = $(MAKE1)
 NETSNMP_CONFIG_SCRIPTS = net-snmp-config
+NETSNMP_AUTORECONF = YES
 
 NETSNMP_BLOAT_MIBS = BRIDGE DISMAN-EVENT DISMAN-SCHEDULE DISMAN-SCRIPT EtherLike RFC-1215 RFC1155-SMI RFC1213 SCTP SMUX
 
@@ -45,6 +46,13 @@ else
 NETSNMP_CONF_OPTS += --with-endianness=little
 endif
 
+ifeq ($(BR2_PACKAGE_LIBNL),y)
+NETSNMP_DEPENDENCIES += host-pkgconf libnl
+NETSNMP_CONF_OPTS += --with-nl
+else
+NETSNMP_CONF_OPTS += --without-nl
+endif
+
 # OpenSSL
 ifeq ($(BR2_PACKAGE_OPENSSL),y)
 NETSNMP_DEPENDENCIES += openssl