Use default kernel export mechanism when symbol lookup is not available

Since kernel 5.7 kallsyms_on_each_symbol() is not available.
NOTE: This affects ability to perform upgrade in flight on kernels 5.7+.

Signed-off-by: Robert Baldyga <robert.baldyga@intel.com>

configure.d/1_kallsyms_on_each_symbol.conf

@@ -0,0 +1,31 @@
+#!/bin/bash
+#
+# Copyright(c) 2012-2020 Intel Corporation
+# SPDX-License-Identifier: BSD-3-Clause-Clear
+#
+
+. $(dirname $3)/conf_framework
+
+check() {
+    cur_name=$(basename $2)
+    config_file_path=$1
+    if compile_module $cur_name "kallsyms_on_each_symbol(NULL, NULL)" "linux/fs.h"
+    then
+        echo $cur_name "1" >> $config_file_path
+    else
+        echo $cur_name "2" >> $config_file_path
+    fi
+}
+
+apply() {
+    case "$1" in
+    "1")
+        add_define "SYMBOL_LOOKUP_SUPPORTED 1" ;;
+    "2")
+        ;;
+    *)
+        exit 1
+    esac
+}
+
+conf_run $@

modules/cas_cache/main.c

@@ -51,6 +51,8 @@ bool in_upgrade;
 ocf_ctx_t cas_ctx;
 struct casdsk_functions_mapper casdisk_functions;
 
+#ifdef SYMBOL_LOOKUP_SUPPORTED
+
 struct exported_symbol {
 	char *name;
 	unsigned long addr;
@@ -74,6 +76,16 @@ int static cas_find_symbol(void *data, const char *namebuf,
              return -EINVAL; \
 })
 
+#else
+
+#include "../cas_disk/cas_disk.h"
+#include "../cas_disk/exp_obj.h"
+#define cas_lookup_symbol(f) ({ \
+	casdisk_functions.f = (void *)f; \
+})
+
+#endif
+
 int static cas_casdisk_lookup_funtions(void)
 {
 	mutex_lock(&module_mutex);