diff --git a/src/cmsg.c b/src/cmsg.c
new file mode 100644
index 0000000..82acda4
--- /dev/null
+++ b/src/cmsg.c
@@ -0,0 +1,29 @@
+#include "common.h"
+#include "cmsg.h"
+
+void
+f2b_cmsg_convert_args(f2b_cmsg_t *msg) {
+  assert(msg != NULL);
+
+  for (size_t i = 0; i < msg->size && i < sizeof(msg->data); i++) {
+    if (msg->data[i] == '\n')
+      msg->data[i] = '\0';
+  }
+}
+
+void
+f2b_cmsg_extract_args(const f2b_cmsg_t *msg, const char **argv) {
+  char prev = '\0';
+  size_t argc = 0;
+
+  assert(msg  != NULL);
+  assert(argv != NULL);
+
+  for (size_t i = 0; i < msg->size; i++) {
+    if (prev == '\0' && msg->data[i] != '\0')
+      argv[argc] = &msg->data[i], argc++;
+    if (argc >= DATA_ARGS_MAX)
+      break;
+    /* next */
+  }
+}
diff --git a/src/cmsg.h b/src/cmsg.h
new file mode 100644
index 0000000..a646376
--- /dev/null
+++ b/src/cmsg.h
@@ -0,0 +1,53 @@
+#ifndef F2B_CMSG_H_
+#define F2B_CMSG_H_
+
+#include <sys/uio.h>
+
+#define DATA_LEN_MAX 496 /* 512 - 16 bytes of header */
+#define DATA_ARGS_MAX 6  /* number of args in data */
+#define F2B_PROTO_VER 1
+
+enum f2b_cmsg_type {
+  CMD_NONE = 0,
+  CMD_RESP,
+  CMD_HELP,
+  CMD_PING = 8,
+  CMD_STATUS,
+  CMD_ROTATE,
+  CMD_RELOAD,
+  CMD_SHUTDOWN,
+  CMD_JAIL_STATUS = 16,
+  CMD_JAIL_SET,
+  CMD_JAIL_IP_SHOW,
+  CMD_JAIL_IP_BAN,
+  CMD_JAIL_IP_RELEASE,
+  CMD_MAX_NUMBER,
+};
+
+#define CMSG_FLAG_NEED_REPLY 0x01
+#define CMSG_FLAG_AUTH_PASS  0x02
+
+/**
+ * @struct f2b control message
+ *
+ * Use sendmsg/recvmsg and iovec structs to pack/unpack
+ */
+typedef struct f2b_cmsg_t {
+  char magic[3];   /**< magic string "F2B" */
+  uint8_t version; /**< protocol version */
+  /* 4 bytes */
+  uint8_t type;    /**< command type, cast from enum f2b_cmsg_type */
+  uint8_t flags;   /**< CMSG_FLAG_* */
+  uint16_t size;   /**< payload length */
+  /* 8 bytes */
+  char pass[8];
+  /* 16 bytes */
+  /* end of header */
+  char data[DATA_LEN_MAX];      /**< set of "\n"-terminated strings */
+  /* end of data */
+} f2b_cmsg_t;
+
+void f2b_cmsg_convert_args(f2b_cmsg_t *msg);
+void f2b_cmsg_extract_args(const f2b_cmsg_t *msg, const char **argv);
+
+#endif /* F2B_CMSG_H_ */