diff --git a/src/backend.c b/src/backend.c
index c46284d..c86d10f 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -7,6 +7,7 @@
 #include "common.h"
 #include "config.h"
 #include "log.h"
+#include "mod-defs.h"
 #include "backend.h"
 
 #include <dlfcn.h>
diff --git a/src/backends/backend.h b/src/backends/backend.h
index 577d633..399ed26 100644
--- a/src/backends/backend.h
+++ b/src/backends/backend.h
@@ -7,14 +7,8 @@
 #include <stdbool.h>
 #include <stdarg.h>
 
-enum loglevel {
-  debug  = 0,
-  info   = 1,
-  notice = 2,
-  warn   = 3,
-  error  = 4,
-  fatal  = 5,
-}; /* see log.h */
+#include "../mod-defs.h"
+#include "../mod-api.h"
 
 /**
  * @file
diff --git a/src/filter.c b/src/filter.c
index fd454dc..8d2306c 100644
--- a/src/filter.c
+++ b/src/filter.c
@@ -7,6 +7,7 @@
 #include "common.h"
 #include "config.h"
 #include "log.h"
+#include "mod-defs.h"
 #include "filter.h"
 
 #include <dlfcn.h>
diff --git a/src/filters/filter.h b/src/filters/filter.h
index 458b462..d0901fb 100644
--- a/src/filters/filter.h
+++ b/src/filters/filter.h
@@ -15,15 +15,8 @@
 #include <string.h>
 
 #include "../strlcpy.h"
-
-enum loglevel {
-  debug  = 0,
-  info   = 1,
-  notice = 2,
-  warn   = 3,
-  error  = 4,
-  fatal  = 5,
-}; /* see log.h */
+#include "../mod-defs.h"
+#include "../mod-api.h"
 
 /**
  * @file
diff --git a/src/mod-api.h b/src/mod-api.h
new file mode 100644
index 0000000..571c306
--- /dev/null
+++ b/src/mod-api.h
@@ -0,0 +1,53 @@
+/** @file This file contains common exportable types and routines used by all modules */
+
+enum loglevel {
+  debug  = 0,
+  info   = 1,
+  notice = 2,
+  warn   = 3,
+  error  = 4,
+  fatal  = 5,
+};
+
+/**
+ * Opaque module handler, contains module internal structs
+ */
+typedef struct _config cfg_t;
+
+/**
+ * @brief Create instance of module
+ * @param init Module-specific init string
+ * @returns Opaque module handler or NULL on failure
+ */
+extern cfg_t *create(const char *init);
+
+/**
+ * @brief Configure module instance
+ * @param cfg Module handler
+ * @param key Parameter name
+ * @param value Parameter value
+ * @returns true on success, false on error
+ */
+extern bool   config(cfg_t *cfg, const char *key, const char *value);
+
+/**
+ * @brief Get internal module state as set of flags (see mod.h)
+ * @param cfg Module handler
+ * @returns <0 on error
+ */
+extern int    state(cfg_t *cfg);
+
+/**
+ * @brief Sets the log callback
+ * @param cfg Module handler
+ * @param cb Logging callback
+ * @note Optional, if this function is not called, warnings/errors of module will be suppressed
+ */
+extern void    logcb(cfg_t *cfg, void (*cb)(enum loglevel l, const char *msg));
+
+/**
+ * @brief Free module handle
+ * @param cfg Module handler
+ * @note Module handler becomes invalid after calling this function on it
+ */
+extern void  destroy(cfg_t *cfg);
diff --git a/src/mod-defs.h b/src/mod-defs.h
new file mode 100644
index 0000000..dc15453
--- /dev/null
+++ b/src/mod-defs.h
@@ -0,0 +1,9 @@
+/** used as in return value of state() call */
+#define MOD_IS_READY          1
+#define MOD_WRONG_API         2
+#define MOD_STARTED           4 /* source, backend */
+#define MOD_NEED_FILTER       8 /* only source */
+/* reserved */
+#define MOD_TYPE_SOURCE    1024 
+#define MOD_TYPE_FILTER    2048
+#define MOD_TYPE_BACKEND   4096
diff --git a/src/source.c b/src/source.c
index 9fe4603..ea52284 100644
--- a/src/source.c
+++ b/src/source.c
@@ -7,11 +7,11 @@
 #include "common.h"
 #include "config.h"
 #include "log.h"
+#include "mod-defs.h"
+#include "source.h"
 
 #include <dlfcn.h>
 
-#include "source.h"
-
 #define SOURCE_LIBRARY_PARAM "load"
 
 f2b_source_t *
diff --git a/src/sources/source.h b/src/sources/source.h
index e005dc8..668431c 100644
--- a/src/sources/source.h
+++ b/src/sources/source.h
@@ -14,15 +14,8 @@
 #include <unistd.h>
 
 #include "../strlcpy.h"
-
-enum loglevel {
-  debug  = 0,
-  info   = 1,
-  notice = 2,
-  warn   = 3,
-  error  = 4,
-  fatal  = 5,
-}; /* see log.h */
+#include "../mod-defs.h"
+#include "../mod-api.h"
 
 /**
  * @file