Provide enum bpf_stats_type if not defined in linux/bpf.h for older kernel

configure.ac

@@ -559,6 +559,25 @@ if test "x${request_libbpf}" != "xno"; then
     # Add the include path for Debian
     EXTRABPFCFLAGS="-I/usr/include/$host_cpu-$host_os"
     AC_SUBST([EXTRABPFCFLAGS])
+
+    AC_MSG_CHECKING([whether enum bpf_stats_type is defined in linux/bpf.h])
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+    [[
+    #include <linux/bpf.h>
+    ]],
+    [[
+    enum bpf_stats_type foo;
+    ]])],
+    [have_bpf_stats_type=yes],
+    [have_bpf_stats_type=no])
+
+    if test "x${have_bpf_stats_type}" = "xyes"; then
+      AC_MSG_RESULT([yes])
+      AC_DEFINE([HAVE_BPF_STATS_TYPE], [1],
+                [Define to 1 if you have enum bpf_stats_type in linux/bpf.h.])
+    else
+      AC_MSG_RESULT([no])
+    fi
   else
     AC_MSG_NOTICE($LIBBPF_PKG_ERRORS)
   fi

src/shrpx.h

@@ -48,4 +48,11 @@
 inline int initgroups(const char *user, gid_t group) { return 0; }
 #endif // defined(HAVE_DECL_INITGROUPS) && !HAVE_DECL_INITGROUPS
 
+#ifndef HAVE_BPF_STATS_TYPE
+/* Newer kernel should have this defined in linux/bpf.h */
+enum bpf_stats_type {
+  BPF_STATS_RUN_TIME = 0,
+};
+#endif // !HAVE_BPF_STATS_TYPE
+
 #endif // SHRPX_H