build: allow disabling eBPF support in n-acd

Add a configure option to disable eBPF support in n-acd.

Note that, even if eBPF is not supported, n-acd requires a kernel >
3.19, which means that the setsockopt(..., SO_ATTACH_BPF) option must
be defined. To allow building on older kernels without modifying the
n-acd code, we inject the SO_ATTACH_BPF value as a preprocessor define
in the compiler the command line.

.travis.yml

@@ -48,7 +48,7 @@ addons:
   coverity_scan:
     project:
       name: NetworkManager/NetworkManager
-    build_command_prepend: sh autogen.sh --with-systemd-logind=no --enable-more-warnings=no --disable-ovs
+    build_command_prepend: sh autogen.sh --with-systemd-logind=no --enable-more-warnings=no --disable-ovs --without-ebpf
     build_command: make -j4
     branch_pattern: .*coverity.*
 
@@ -114,6 +114,7 @@ script:
               -D ifcfg_rh=false \
               -D ibft=true \
               -D ifupdown=true \
+              -D ebpf=false \
               &&
           ninja -C build &&
           ninja -C build test
@@ -136,6 +137,7 @@ script:
               --enable-more-warnings=no \
               --enable-tests=yes \
               --with-crypto=$CRYPTO \
+              --without-ebpf \
               \
               --with-libnm-glib=yes \
               --with-iwd=yes \

Makefile.am

@@ -1370,6 +1370,7 @@ shared_libnacd_la_LIBADD = shared/libcrbtree.la
 
 shared_libnacd_la_CPPFLAGS = \
 	-D_GNU_SOURCE \
+	-DSO_ATTACH_BPF=50 \
 	$(CODE_COVERAGE_CFLAGS) \
 	$(SANITIZER_LIB_CFLAGS) \
 	-I$(srcdir)/shared/c-list/src \
@@ -1380,12 +1381,17 @@ shared_libnacd_la_CPPFLAGS = \
 shared_libnacd_la_SOURCES = \
 	shared/n-acd/src/n-acd.c \
 	shared/n-acd/src/n-acd.h \
-	shared/n-acd/src/n-acd-bpf.c \
 	shared/n-acd/src/n-acd-private.h \
 	shared/n-acd/src/n-acd-probe.c \
 	shared/n-acd/src/util/timer.c \
 	shared/n-acd/src/util/timer.h
 
+if WITH_EBPF
+shared_libnacd_la_SOURCES += shared/n-acd/src/n-acd-bpf.c
+else
+shared_libnacd_la_SOURCES += shared/n-acd/src/n-acd-bpf-fallback.c
+endif
+
 EXTRA_DIST += shared/c-list/src/c-list.h
 
 ###############################################################################

configure.ac

@@ -518,6 +518,15 @@ case $with_suspend_resume in
 		;;
 esac
 
+# eBPF support
+AC_ARG_WITH(ebpf,
+            AS_HELP_STRING([--with-ebpf=yes|no], [Build with eBPF support (default: yes)]),
+            [], [with_ebpf=yes])
+if test "$with_ebpf" != "yes" -a "$with_ebpf" != "no"; then
+	AC_MSG_ERROR(--with-ebpf must be one of [yes, no])
+fi
+AM_CONDITIONAL(WITH_EBPF, test "${with_ebpf}" = "yes")
+
 # SELinux support
 AC_ARG_WITH(selinux,
             AS_HELP_STRING([--with-selinux=yes|no|auto], [Build with SELinux (default: auto)]),
@@ -1353,4 +1362,5 @@ echo "  JSON validation for libnm: $enable_json_validation"
 echo "  crypto: $with_crypto (have-gnutls: $have_crypto_gnutls, have-nss: $have_crypto_nss)"
 echo "  sanitizers: $sanitizers"
 echo "  Mozilla Public Suffix List: $with_libpsl"
+echo "  eBPF: $with_ebpf"
 echo

meson_options.txt

@@ -41,6 +41,7 @@ option('libnm_glib', type: 'boolean', value: false, description: 'build legacy l
 option('nmcli', type: 'boolean', value: true, description: 'Build nmcli')
 option('nmtui', type: 'boolean', value: true, description: 'Build nmtui')
 option('bluez5_dun', type: 'boolean', value: false, description: 'enable Bluez5 DUN support')
+option('ebpf', type: 'boolean', value: true, description: 'Enable or disable eBPF support')
 
 # configuration plugins
 option('config_plugins_default', type: 'string', value: '', description: 'Default configuration option for main.plugins setting, used as fallback if the configuration option is unset')

shared/meson.build

@@ -23,17 +23,25 @@ shared_c_rbtree_dep = declare_dependency(
     link_with: shared_c_rbtree,
 )
 
+
+if get_option('ebpf')
+    shared_n_acd_bpf_files = files('n-acd/src/n-acd-bpf.c')
+else
+    shared_n_acd_bpf_files = files('n-acd/src/n-acd-bpf-fallback.c')
+endif
+
 shared_n_acd = static_library(
     'n-acd',
     sources: files('n-acd/src/n-acd.c',
                    'n-acd/src/n-acd.h',
-                   'n-acd/src/n-acd-bpf.c',
                    'n-acd/src/n-acd-private.h',
                    'n-acd/src/n-acd-probe.c',
                    'n-acd/src/util/timer.c',
-                   'n-acd/src/util/timer.h'),
+                   'n-acd/src/util/timer.h')
+             + shared_n_acd_bpf_files,
     c_args: [
         '-D_GNU_SOURCE',
+        '-DSO_ATTACH_BPF=50',
         '-std=c11',
         '-Wno-pointer-arith',
         '-Wno-vla',