diff --git a/functional-tests/device-mapper/Makefile b/functional-tests/device-mapper/Makefile
new file mode 100644
index 0000000..0102820
--- /dev/null
+++ b/functional-tests/device-mapper/Makefile
@@ -0,0 +1,11 @@
+dm-ioctl.so: dm-ioctl.o
+	gcc -shared -o $@ $< -laio
+
+dm-ioctl.o: dm-ioctl.c
+	gcc -std=gnu11 -fpic -I. -Wall -c -o $@ $<
+
+.PHONEY: clean
+clean:
+	rm -f dm-ioctl.so dm-ioctl.o
+
+
diff --git a/functional-tests/device-mapper/dm-ioctl.c b/functional-tests/device-mapper/dm-ioctl.c
new file mode 100644
index 0000000..d643199
--- /dev/null
+++ b/functional-tests/device-mapper/dm-ioctl.c
@@ -0,0 +1,573 @@
+#include <linux/dm-ioctl.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <stdio.h>
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+//----------------------------------------------------------------
+
+// assuming div is a power of 2
+static size_t round_up(size_t n, size_t div)
+{
+	size_t mask = div - 1;
+	return (n + mask) & ~mask;
+}
+
+//----------------------------------------------------------------
+
+static void *zalloc(size_t len)
+{
+	void *ptr = malloc(len);
+	if (ptr)
+		memset(ptr, 0, len);
+
+	return ptr;
+}
+
+static void *payload(struct dm_ioctl *ctl)
+{
+	return ((unsigned char *) ctl) + ctl->data_start;
+}
+
+static struct dm_ioctl *alloc_ctl(size_t payload_size)
+{
+	size_t len = sizeof(struct dm_ioctl) + payload_size;
+	struct dm_ioctl *ctl = zalloc(len);
+
+	if (ctl) {
+		ctl->version[0] = DM_VERSION_MAJOR;
+		ctl->version[1] = DM_VERSION_MINOR;
+		ctl->version[2] = DM_VERSION_PATCHLEVEL;
+		ctl->data_size = len;
+		ctl->data_start = sizeof(*ctl);
+	}
+
+	return ctl;
+}
+
+static void free_ctl(struct dm_ioctl *ctl)
+{
+	free(ctl);
+}
+
+// realloc only copies the dm_ioctl struct, not the payload.
+// old is always freed, even in case of error.
+static struct dm_ioctl *realloc_ctl(struct dm_ioctl *old, size_t extra_payload)
+{
+	struct dm_ioctl *ctl;
+	size_t old_payload_size = old->data_size - sizeof(struct dm_ioctl);
+	size_t new_payload_size = old_payload_size + extra_payload;
+
+	ctl = alloc_ctl(new_payload_size);
+	if (ctl)
+		memcpy(payload(ctl), payload(old), sizeof(*ctl));
+
+	free_ctl(old);
+	return ctl;
+}
+
+//----------------------------------------------------------------
+
+struct dm_interface {
+	int fd;
+};
+
+// FIXME: pass in some form of log object?
+struct dm_interface *dm_open()
+{
+	int fd;
+	char path[1024];
+	struct dm_interface *dmi;
+
+	snprintf(path, sizeof(path), "/dev/%s/%s", DM_DIR, DM_CONTROL_NODE);
+	fd = open(path, O_RDWR | O_EXCL);
+	if (fd < 0)
+		return NULL;
+
+	dmi = zalloc(sizeof(*dmi));
+	if (dmi)
+		dmi->fd = fd;
+	else
+		close(fd);
+
+	return dmi;
+}
+
+void dm_close(struct dm_interface *dmi)
+{
+	close(dmi->fd);
+	free(dmi);
+}
+
+//----------------------------------------------------------------
+
+struct dev_list {
+	struct dev_list *next;
+	unsigned major;
+	unsigned minor;
+	char *name;
+};
+
+void free_dev_list(struct dev_list *dl)
+{
+	struct dev_list *next;
+
+	while (dl) {
+		next = dl->next;
+		free(dl->name);
+		free(dl);
+		dl = next;
+	}
+}
+
+struct dev_list_builder {
+	struct dev_list *head, *tail;
+};
+
+static void dlb_init(struct dev_list_builder *dlb)
+{
+	dlb->head = dlb->tail = NULL;
+}
+
+static int dlb_append(struct dev_list_builder *dlb,
+		      unsigned major, unsigned minor, const char *name)
+{
+	struct dev_list *dl = malloc(sizeof(*dl));
+
+	if (!dl)
+		return -ENOMEM;
+
+	dl->major = major;
+	dl->minor = minor;
+	dl->name = strdup(name);
+
+	if (dlb->head) {
+		dlb->tail->next = dl;
+		dlb->tail = dl;
+	} else
+		dlb->head = dlb->tail = dl;
+
+	return 0;
+}
+
+static struct dev_list *dlb_get(struct dev_list_builder *dlb)
+{
+	return dlb->head;
+}
+
+//----------------------------------------------------------------
+
+static int copy_string(char *dest, const char *src, size_t max)
+{
+	if (strlen(src) + 1 > max)
+		return -ENOMEM;
+
+	strcpy(dest, src);
+	return 0;
+}
+
+static int copy_name(struct dm_ioctl *ctl, const char *name)
+{
+	return copy_string(ctl->name, name, DM_NAME_LEN);
+}
+
+static int copy_uuid(struct dm_ioctl *ctl, const char *uuid)
+{
+	return copy_string(ctl->uuid, uuid, DM_UUID_LEN);
+}
+
+//----------------------------------------------------------------
+
+int dm_version(struct dm_interface *dmi, uint32_t *major, uint32_t *minor, uint32_t *patch)
+{
+	int r;
+	struct dm_ioctl *ctl = alloc_ctl(0);
+
+	if (!ctl)
+		return -ENOMEM;
+
+	r = ioctl(dmi->fd, DM_VERSION, ctl);
+	*major = ctl->version[0];
+	*minor = ctl->version[1];
+	*patch = ctl->version[2];
+	free_ctl(ctl);
+
+	return r;
+}
+
+int dm_remove_all(struct dm_interface *dmi)
+{
+	int r;
+	struct dm_ioctl *ctl = alloc_ctl(0);
+
+	if (!ctl)
+		return -ENOMEM;
+
+	r = ioctl(dmi->fd, DM_REMOVE_ALL, ctl);
+	free_ctl(ctl);
+
+	return r;
+}
+
+static bool list_devices(struct dm_interface *dmi, struct dm_ioctl *ctl,
+			 size_t payload_size, struct dev_list **devs,
+			 int *r)
+{
+	struct dm_name_list *nl;
+	struct dev_list_builder dlb;
+
+	*r = ioctl(dmi->fd, DM_LIST_DEVICES, ctl);
+	if (*r < 0)
+		return true;
+
+	if (ctl->flags & DM_BUFFER_FULL_FLAG) {
+		free_ctl(ctl);
+		return false;
+	}
+
+	dlb_init(&dlb);
+	nl = (struct dm_name_list *) payload(ctl);
+
+	if (nl->dev) {
+		for (;;) {
+			dlb_append(&dlb, major(nl->dev), minor(nl->dev), nl->name);
+
+			if (!nl->next)
+				break;
+
+			nl = (struct dm_name_list *) (((unsigned char *) nl) + nl->next);
+		}
+	}
+
+	*devs = dlb_get(&dlb);
+	return true;
+}
+
+int dm_list_devices(struct dm_interface *dmi, struct dev_list **devs)
+{
+	int r;
+	struct dm_ioctl *ctl;
+	size_t payload_size = 8192;
+
+	ctl = alloc_ctl(payload_size);
+	if (!ctl)
+		return -ENOMEM;
+
+	while (!list_devices(dmi, ctl, payload_size, devs, &r)) {
+		payload_size *= 2;
+		ctl = realloc_ctl(ctl, payload_size);
+		if (!ctl)
+			return -ENOMEM;
+	}
+	free_ctl(ctl);
+
+	return r;
+}
+
+int dm_create_device(struct dm_interface *dmi, const char *name, const char *uuid)
+{
+	int r;
+	struct dm_ioctl *ctl = alloc_ctl(0);
+
+	if (!ctl)
+		return -ENOMEM;
+
+	r = copy_name(ctl, name);
+	if (r) {
+		free_ctl(ctl);
+		return r;
+	}
+
+	r = copy_uuid(ctl, name);
+	if (r) {
+		free_ctl(ctl);
+		return r;
+	}
+
+	r = ioctl(dmi->fd, DM_DEV_CREATE, ctl);
+	free_ctl(ctl);
+
+	return r;
+}
+
+static int dev_cmd(struct dm_interface *dmi, const char *name, int request, unsigned flags)
+{
+	int r;
+	struct dm_ioctl *ctl = alloc_ctl(0);
+	ctl->flags = flags;
+	r = copy_name(ctl, name);
+	if (r) {
+		free_ctl(ctl);
+		return -ENOMEM;
+	}
+	r = ioctl(dmi->fd, request);
+	free_ctl(ctl);
+
+	return r;
+}
+
+int dm_remove_device(struct dm_interface *dmi, const char *name)
+{
+	return dev_cmd(dmi, name, DM_DEV_REMOVE, 0);
+}
+
+int dm_suspend_device(struct dm_interface *dmi, const char *name)
+{
+	return dev_cmd(dmi, name, DM_DEV_SUSPEND, DM_SUSPEND_FLAG);
+}
+
+int dm_resume_device(struct dm_interface *dmi, const char *name)
+{
+	return dev_cmd(dmi, name, DM_DEV_SUSPEND, 0);
+}
+
+int dm_clear_device(struct dm_interface *dmi, const char *name)
+{
+	return dev_cmd(dmi, name, DM_TABLE_CLEAR, 0);
+}
+
+//----------------------------------------------------------------
+
+struct target {
+	struct target *next;
+
+	uint64_t len;
+	char *type;
+	char *args;
+};
+
+void free_targets(struct target *t)
+{
+	while (t) {
+		struct target *next = t->next;
+		free(t->type);
+		free(t->args);
+		t = next;
+	}
+}
+
+struct target_builder {
+	struct target *head, *tail;
+};
+
+static void tb_init(struct target_builder *tb)
+{
+	tb->head = tb->tail = NULL;
+}
+
+static int tb_append(struct target_builder *tb, uint64_t len, char *type, char *args)
+{
+	struct target *t = malloc(sizeof(*t));
+	if (!t)
+		return -ENOMEM;
+
+	t->next = NULL;
+	t->len = len;
+	t->type = strdup(type);
+	t->args = strdup(args);
+
+	if (tb->head) {
+		tb->tail->next = t;
+		tb->tail = t;
+	} else
+		tb->head = tb->tail = t;
+
+	return 0;
+}
+
+static struct target *tb_get(struct target_builder *tb)
+{
+	return tb->head;
+}
+
+//----------------------------------------------------------------
+// FIXME: provide some way of freeing a target list.
+// FIXME: check the result from alloc_ctl is always being checked.
+
+static size_t calc_load_payload(struct target *t)
+{
+	size_t space = 0;
+
+	while (t) {
+		space += sizeof(struct dm_target_spec);
+		space += strlen(t->args) + 16;
+		t = t->next;
+	}
+
+	return space + 128;
+}
+
+static int prep_load(struct dm_ioctl *ctl, size_t payload_size,
+		     const char *name, struct target *t)
+{
+	int r;
+	uint64_t current_sector = 0;
+	struct dm_target_spec *spec;
+
+	spec = payload(ctl);
+
+	while (t) {
+		spec->sector_start = current_sector;
+		current_sector += t->len;
+		spec->length = t->len;
+		spec->status = 0;
+		r = copy_string(spec->target_type, t->type, DM_MAX_TYPE_NAME);
+		if (r)
+			return r;
+
+		r = copy_string((char *) spec + 1, t->args, payload_size);
+		if (r)
+			return r;
+
+		spec->next = sizeof(*spec) + round_up(strlen(t->args) + 1, 8);
+		payload_size -= spec->next;
+		spec = (struct dm_target_spec *) (((char *) spec) + spec->next);
+
+		t = t->next;
+	}
+
+	return true;
+}
+
+int dm_load(struct dm_interface *dmi, const char *name,
+	    struct target *targets)
+{
+	int r;
+	size_t payload_size = calc_load_payload(targets);
+	struct dm_ioctl *ctl = alloc_ctl(payload_size);
+
+	if (!ctl)
+		return -ENOMEM;
+
+	r = prep_load(ctl, payload_size, name, targets);
+	if (r) {
+		free_ctl(ctl);
+		return r;
+	}
+
+	r = copy_name(ctl, name);
+	if (r) {
+		free_ctl(ctl);
+		return -ENOMEM;
+	}
+
+	r = ioctl(dmi->fd, DM_TABLE_LOAD, ctl);
+	free_ctl(ctl);
+
+	return r;
+}
+
+//----------------------------------------------------------------
+// returns false if control buffer too small.
+static bool get_status(struct dm_interface *dmi, struct dm_ioctl *ctl,
+		       const char *name, unsigned flags,
+		       int *result)
+{
+	*result = copy_name(ctl, name);
+	if (*result) {
+		free_ctl(ctl);
+		return true;
+	}
+
+	ctl->flags = flags;
+	ctl->target_count = 0;
+
+	*result = ioctl(dmi->fd, DM_TABLE_STATUS, ctl);
+	if (*result)
+		return true;
+
+	if (ctl->flags & DM_BUFFER_FULL_FLAG)
+		return false;
+
+	return true;
+}
+
+static int unpack_status(struct dm_ioctl *ctl, struct target **result)
+{
+	unsigned i;
+	struct target_builder tb;
+	struct dm_target_spec *spec = payload(ctl);
+
+	tb_init(&tb);
+	for (i = 0; i < ctl->target_count; i++) {
+		tb_append(&tb, spec->length, spec->target_type, (char *) (spec + 1));
+		spec = (struct dm_target_spec *) (((char *) spec) + spec->next);
+	}
+
+	*result = tb_get(&tb);
+	return 0;
+}
+
+static int status_cmd(struct dm_interface *dmi, const char *name,
+		      struct target **targets, unsigned flags)
+{
+	int r;
+	size_t payload_size = 8192;
+	struct dm_ioctl *ctl = NULL;
+
+	ctl = alloc_ctl(payload_size);
+	if (!ctl)
+		return -ENOMEM;
+
+retry:
+	if (!get_status(dmi, ctl, name, flags, &r)) {
+		payload_size *= 2;
+		ctl = realloc_ctl(ctl, payload_size);
+		if (!ctl)
+			return -ENOMEM;
+
+		goto retry;
+	}
+
+	r = unpack_status(ctl, targets);
+	free_ctl(ctl);
+	return r;
+}
+
+int dm_status(struct dm_interface *dmi, const char *name, struct target **targets)
+{
+	return status_cmd(dmi, name, targets, 0);
+}
+
+int dm_table(struct dm_interface *dmi, const char *name, struct target **targets)
+{
+	return status_cmd(dmi, name, targets, DM_STATUS_TABLE_FLAG);
+}
+
+#if 0
+int dm_info(struct dm_interface *dmi, const char *name, struct target **targets)
+{
+	return status_cmd(dmi, name, targets, DM_STATUS_INFO_FLAG);
+}
+#endif
+
+int dm_message(struct dm_interface *dmi, const char *name, uint64_t sector,
+	       const char *msg_str)
+{
+	int r;
+	size_t msg_len = strlen(msg_str) + 1;
+	size_t payload_size = msg_len + 32;
+	struct dm_ioctl *ctl = alloc_ctl(payload_size);
+	struct dm_target_msg *msg;
+
+	if (!ctl)
+		return -ENOMEM;
+	msg = payload(ctl);
+	copy_name(ctl, name);
+	msg->sector = sector;
+	memcpy(msg->message, msg_str, msg_len);
+
+	r = ioctl(dmi->fd, DM_TARGET_MSG, ctl);
+	free_ctl(ctl);
+
+	return r;
+}
+
+//----------------------------------------------------------------
diff --git a/functional-tests/device-mapper/dm-tests.scm b/functional-tests/device-mapper/dm-tests.scm
new file mode 100644
index 0000000..1c174cc
--- /dev/null
+++ b/functional-tests/device-mapper/dm-tests.scm
@@ -0,0 +1,22 @@
+(library
+  (device-mapper dm-tests)
+  (export register-dm-tests)
+  (import (device-mapper ioctl)
+          (chezscheme)
+          (functional-tests)
+          (fmt fmt)
+          (process)
+          (temp-file))
+  
+  ;; We have to export something that forces all the initialisation expressions
+  ;; to run.
+  (define (register-dm-tests) #t)
+
+  ;;;-----------------------------------------------------------
+  ;;; scenarios
+  ;;;-----------------------------------------------------------
+  (define-scenario (dm create-interface)
+                   "create and destroy an ioctl interface object"
+                   (with-dm (dm) #t))
+
+  )
diff --git a/functional-tests/device-mapper/ioctl.scm b/functional-tests/device-mapper/ioctl.scm
new file mode 100644
index 0000000..bf5c37b
--- /dev/null
+++ b/functional-tests/device-mapper/ioctl.scm
@@ -0,0 +1,78 @@
+(library
+  (device-mapper ioctl)
+
+  (export dm-open
+          dm-close
+          with-dm
+
+          get-version)
+
+  (import (chezscheme)
+          (fmt fmt)
+          (srfi s8 receive)
+          (utils))
+
+  (define __ (load-shared-object "./device-mapper/dm-ioctl.so"))
+
+  (define (fail msg)
+    (raise
+      (condition
+        (make-error)
+        (make-message-condition msg))))
+
+  (define-ftype DMIoctlInterface
+    (struct
+      (fd int)))
+
+  (define open% (foreign-procedure "dm_open" () (* DMIoctlInterface)))
+
+  (define (dm-open)
+    (let ((ptr (open%)))
+     (if (ftype-pointer-null? ptr)
+         (fail "couldn't open ioctl interface (permissions?)")
+         ptr)))
+
+  (define dm-close
+    (foreign-procedure "dm_close" ((* DMIoctlInterface)) void))
+
+  (define-syntax with-dm
+    (syntax-rules ()
+      ((_ (name) b1 b2 ...)
+       (let ((name (dm-open)))
+        (dynamic-wind
+          (lambda () #f)
+          (lambda () b1 b2 ...)
+          (lambda () (dm-close name)))))))
+
+  (define-record-type dm-version (fields major minor patch))
+
+  (define-ftype PtrU32 (* unsigned-32))
+
+  (define (get-version dm)
+    (define get
+      (foreign-procedure "dm_version" ((* DMIoctlInterface)
+                                       (* unsigned-32)
+                                       (* unsigned-32)
+                                       (* unsigned-32)) int))
+
+    (define (alloc-u32)
+      (make-ftype-pointer unsigned-32
+        (foreign-alloc (ftype-sizeof unsigned-32))))
+
+    (define (deref-u32 p)
+      (ftype-ref unsigned-32 () p))
+
+    (let ((major (alloc-u32))
+          (minor (alloc-u32))
+          (patch (alloc-u32)))
+      (get dm major minor patch)
+      (let ((r (make-dm-version (deref-u32 major)
+                                (deref-u32 minor)
+                                (deref-u32 patch))))
+        (foreign-free (ftype-pointer-address major))
+        (foreign-free (ftype-pointer-address minor))
+        (foreign-free (ftype-pointer-address patch))
+        r)))
+
+
+)
diff --git a/functional-tests/run-tests b/functional-tests/run-tests
index c08f40f..333ea90 100755
--- a/functional-tests/run-tests
+++ b/functional-tests/run-tests
@@ -7,6 +7,7 @@
         (functional-tests)
 	(bcache bcache-tests)
         (cache-functional-tests)
+        (device-mapper dm-tests)
         (era-functional-tests)
         (parser-combinators)
         (only (srfi s1 lists) break)
@@ -179,6 +180,7 @@
 (register-cache-tests)
 (register-era-tests)
 (register-bcache-tests)
+(register-dm-tests)
 
 (with-dir "test-output"
  ((parse-command-line)))