diff --git a/include/splat-ctl.h b/include/splat-ctl.h
new file mode 100644
index 000000000..d905340fb
--- /dev/null
+++ b/include/splat-ctl.h
@@ -0,0 +1,67 @@
+#ifndef _SPLAT_CTL_H
+#define _SPLAT_CTL_H
+
+/* Contains shared definitions which both the userspace
+ * and kernelspace portions of splat must agree on.
+ */
+
+#define SPLAT_MAJOR			229 /* XXX - Arbitrary */
+#define SPLAT_MINORS                    1
+#define SPLAT_DEV			"/dev/splatctl"
+
+#define SPLAT_NAME_SIZE			12
+#define SPLAT_DESC_SIZE			60
+
+typedef struct splat_user {
+	char name[SPLAT_NAME_SIZE];	/* short name */
+	char desc[SPLAT_DESC_SIZE];	/* short description */
+	int id;				/* unique numeric id */
+} splat_user_t;
+
+#define	SPLAT_CFG_MAGIC			0x15263748U
+typedef struct splat_cfg {
+	unsigned int cfg_magic;		/* Unique magic */
+	int cfg_cmd;			/* Config command */
+	int cfg_arg1;			/* Config command arg 1 */
+	int cfg_rc1;			/* Config response 1 */
+	union {
+		struct {
+			int size;
+			splat_user_t descs[0];
+		} splat_subsystems;
+		struct {
+			int size;
+			splat_user_t descs[0];
+		} splat_tests;
+	} cfg_data;
+} splat_cfg_t;
+
+#define	SPLAT_CMD_MAGIC			0x9daebfc0U
+typedef struct splat_cmd {
+	unsigned int cmd_magic;		/* Unique magic */
+	int cmd_subsystem;		/* Target subsystem */
+	int cmd_test;			/* Subsystem test */
+	int cmd_data_size;		/* Extra opaque data */
+	char cmd_data_str[0];		/* Opaque data region */
+} splat_cmd_t;
+
+/* Valid ioctls */
+#define SPLAT_CFG				_IOWR('f', 101, long)
+#define SPLAT_CMD				_IOWR('f', 102, long)
+
+/* Valid configuration commands */
+#define SPLAT_CFG_BUFFER_CLEAR		0x001	/* Clear text buffer */
+#define SPLAT_CFG_BUFFER_SIZE		0x002	/* Resize text buffer */
+#define SPLAT_CFG_SUBSYSTEM_COUNT		0x101	/* Number of subsystem */
+#define SPLAT_CFG_SUBSYSTEM_LIST		0x102	/* List of N subsystems */
+#define SPLAT_CFG_TEST_COUNT		0x201	/* Number of tests */
+#define SPLAT_CFG_TEST_LIST		0x202	/* List of N tests */
+
+/* Valid subsystem and test commands defined in each subsystem, we do
+ * need to be careful to avoid colisions.  That alone may argue to define
+ * them all here, for now we just define the global error codes.
+ */
+#define SPLAT_SUBSYSTEM_UNKNOWN		0xF00
+#define SPLAT_TEST_UNKNOWN		0xFFF
+
+#endif /* _SPLAT_CTL_H */