[PATCHv3 iproute2-next 1/5] configure: add check_libbpf() for later libbpf support

[Hangbin Liu <haliu@xxxxxxxxxx>]

This patch adds a check to see if we support libbpf. By default the
system libbpf will be used, but static linking against a custom libbpf
version can be achieved by passing LIBBPF_DIR to configure. FORCE_LIBBPF
can be set to force configure to abort if no suitable libbpf is found,
which is useful for automatic packaging that wants to enforce the
dependency.

Signed-off-by: Hangbin Liu <haliu@xxxxxxxxxx>
---
v3:
Check function bpf_program__section_name() separately and only use it
on higher libbpf version.

v2:
No update
---
 configure | 94 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)

diff --git a/configure b/configure
index 307912aa..58a7176e 100755
--- a/configure
+++ b/configure
@@ -240,6 +240,97 @@ check_elf()
     fi
 }
 
+have_libbpf_basic()
+{
+    cat >$TMPDIR/libbpf_test.c <<EOF
+#include <bpf/libbpf.h>
+int main(int argc, char **argv) {
+    bpf_program__set_autoload(NULL, false);
+    bpf_map__ifindex(NULL);
+    bpf_map__set_pin_path(NULL, NULL);
+    bpf_object__open_file(NULL, NULL);
+    return 0;
+}
+EOF
+
+    $CC -o $TMPDIR/libbpf_test $TMPDIR/libbpf_test.c $LIBBPF_CFLAGS $LIBBPF_LDLIBS >/dev/null 2>&1
+    local ret=$?
+
+    rm -f $TMPDIR/libbpf_test.c $TMPDIR/libbpf_test
+    return $ret
+}
+
+have_libbpf_sec_name()
+{
+    cat >$TMPDIR/libbpf_sec_test.c <<EOF
+#include <bpf/libbpf.h>
+int main(int argc, char **argv) {
+    void *ptr;
+    bpf_program__section_name(NULL);
+    return 0;
+}
+EOF
+
+    $CC -o $TMPDIR/libbpf_sec_test $TMPDIR/libbpf_sec_test.c $LIBBPF_CFLAGS $LIBBPF_LDLIBS >/dev/null 2>&1
+    local ret=$?
+
+    rm -f $TMPDIR/libbpf_sec_test.c $TMPDIR/libbpf_sec_test
+    return $ret
+}
+
+check_force_libbpf()
+{
+    # if set FORCE_LIBBPF but no libbpf support, just exist the config
+    # process to make sure we don't build without libbpf.
+    if [ -n "$FORCE_LIBBPF" ]; then
+        echo "FORCE_LIBBPF set, but couldn't find a usable libbpf"
+        exit 1
+    fi
+}
+
+check_libbpf()
+{
+    if ! ${PKG_CONFIG} libbpf --exists && [ -z "$LIBBPF_DIR" ] ; then
+        echo "no"
+        check_force_libbpf
+        return
+    fi
+
+    if [ $(uname -m) == x86_64 ]; then
+        local LIBSUBDIR=lib64
+    else
+        local LIBSUBDIR=lib
+    fi
+
+    if [ -n "$LIBBPF_DIR" ]; then
+        LIBBPF_CFLAGS="-I${LIBBPF_DIR}/include -L${LIBBPF_DIR}/${LIBSUBDIR}"
+        LIBBPF_LDLIBS="${LIBBPF_DIR}/${LIBSUBDIR}/libbpf.a -lz -lelf"
+    else
+        LIBBPF_CFLAGS=$(${PKG_CONFIG} libbpf --cflags)
+        LIBBPF_LDLIBS=$(${PKG_CONFIG} libbpf --libs)
+    fi
+
+    if ! have_libbpf_basic; then
+        echo "no"
+        echo "	libbpf version is too low, please update it to at least 0.1.0"
+        check_force_libbpf
+        return
+    else
+        echo "HAVE_LIBBPF:=y" >>$CONFIG
+        echo 'CFLAGS += -DHAVE_LIBBPF ' $LIBBPF_CFLAGS >> $CONFIG
+        echo 'LDLIBS += ' $LIBBPF_LDLIBS >>$CONFIG
+    fi
+
+    # bpf_program__title() is deprecated since libbpf 0.2.0, use
+    # bpf_program__section_name() instead if we support
+    if have_libbpf_sec_name; then
+        echo "HAVE_LIBBPF_SECTION_NAME:=y" >>$CONFIG
+        echo 'CFLAGS += -DHAVE_LIBBPF_SECTION_NAME ' $LIBBPF_CFLAGS >> $CONFIG
+    fi
+
+    echo "yes"
+}
+
 check_selinux()
 # SELinux is a compile time option in the ss utility
 {
@@ -385,6 +476,9 @@ check_setns
 echo -n "SELinux support: "
 check_selinux
 
+echo -n "libbpf support: "
+check_libbpf
+
 echo -n "ELF support: "
 check_elf
 
-- 
2.25.4