[PATCHv2 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.

Reviewed-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Signed-off-by: Hangbin Liu <haliu@xxxxxxxxxx>
---
 configure | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/configure b/configure
index 307912aa..77f475d9 100755
--- a/configure
+++ b/configure
@@ -240,6 +240,51 @@ check_elf()
     fi
 }
 
+check_libbpf()
+{
+    if ${PKG_CONFIG} libbpf --exists || [ -n "$LIBBPF_DIR" ] ; then
+
+        if [ -n "$LIBBPF_DIR" ]; then
+            LIBBPF_CFLAGS="-I${LIBBPF_DIR}/include -L${LIBBPF_DIR}/lib64"
+            LIBBPF_LDLIBS="${LIBBPF_DIR}/lib64/libbpf.a -lz -lelf"
+        else
+            LIBBPF_CFLAGS=$(${PKG_CONFIG} libbpf --cflags)
+            LIBBPF_LDLIBS=$(${PKG_CONFIG} libbpf --libs)
+        fi
+
+        cat >$TMPDIR/libbpftest.c <<EOF
+#include <bpf/libbpf.h>
+int main(int argc, char **argv) {
+    void *ptr;
+    DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts, .relaxed_maps = true, .pin_root_path = "/path");
+    (void) bpf_object__open_file("file", &opts);
+    (void) bpf_map__name(ptr);
+    (void) bpf_map__ifindex(ptr);
+    (void) bpf_map__reuse_fd(ptr, 0);
+    (void) bpf_map__pin(ptr, "/path");
+    return 0;
+}
+EOF
+
+        if $CC -o $TMPDIR/libbpftest $TMPDIR/libbpftest.c $LIBBPF_CFLAGS -lbpf 2>&1; then
+            echo "HAVE_LIBBPF:=y" >>$CONFIG
+            echo 'CFLAGS += -DHAVE_LIBBPF ' $LIBBPF_CFLAGS >> $CONFIG
+            echo 'LDLIBS += ' $LIBBPF_LDLIBS >>$CONFIG
+            echo "yes"
+            return 0
+        fi
+    fi
+
+    echo "no"
+
+    # 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_selinux()
 # SELinux is a compile time option in the ss utility
 {
@@ -385,6 +430,9 @@ check_setns
 echo -n "SELinux support: "
 check_selinux
 
+echo -n "libbpf support: "
+check_libbpf
+
 echo -n "ELF support: "
 check_elf
 
-- 
2.25.4