diff --git a/src/device-private.h b/src/device-private.h
index 4ee4f20..056dd41 100644
--- a/src/device-private.h
+++ b/src/device-private.h
@@ -14,6 +14,9 @@ typedef struct device_backend_t device_backend_t;
 
 struct device_t {
 	const device_backend_t *backend;
+	// Progress callback data.
+	progress_callback_t progress;
+	void *userdata;
 };
 
 struct device_backend_t {
@@ -34,6 +37,23 @@ struct device_backend_t {
 	device_status_t (*close) (device_t *device);
 };
 
+#define INFINITE ((unsigned int)-1)
+
+typedef struct device_progress_state_t {
+	progress_callback_t callback;
+	void *userdata;
+	unsigned int current, maximum;
+} device_progress_state_t;
+
+void
+progress_init (device_progress_state_t *progress, device_t *device, unsigned int maximum);
+
+void
+progress_event (device_progress_state_t *progress, device_event_t event, unsigned int value);
+
+void
+progress_set_maximum (device_progress_state_t *progress, unsigned int value);
+
 void
 device_init (device_t *device, const device_backend_t *backend);
 
diff --git a/src/device.c b/src/device.c
index de96168..2c1dfd5 100644
--- a/src/device.c
+++ b/src/device.c
@@ -1,3 +1,5 @@
+#include <assert.h>
+
 #include "device-private.h"
 
 #define NULL 0
@@ -7,6 +9,8 @@ void
 device_init (device_t *device, const device_backend_t *backend)
 {
 	device->backend = backend;
+	device->progress = NULL;
+	device->userdata = NULL;
 }
 
 
@@ -20,6 +24,19 @@ device_get_type (device_t *device)
 }
 
 
+device_status_t
+device_set_progress (device_t *device, progress_callback_t callback, void *userdata)
+{
+	if (device == NULL)
+		return DEVICE_STATUS_UNSUPPORTED;
+
+	device->progress = callback;
+	device->userdata = userdata;
+
+	return DEVICE_STATUS_SUCCESS;
+}
+
+
 device_status_t
 device_handshake (device_t *device, unsigned char data[], unsigned int size)
 {
@@ -109,3 +126,53 @@ device_close (device_t *device)
 
 	return device->backend->close (device);
 }
+
+
+void
+progress_init (device_progress_state_t *progress, device_t *device, unsigned int maximum)
+{
+	if (progress == NULL)
+		return;
+
+	progress->callback = (device ? device->progress : NULL);
+	progress->userdata = (device ? device->userdata : NULL);
+	progress->maximum = maximum;
+	progress->current = 0;
+}
+
+
+void
+progress_event (device_progress_state_t *progress, device_event_t event, unsigned int value)
+{
+	if (progress == NULL)
+		return;
+
+	switch (event) {
+	case DEVICE_EVENT_WAITING:
+		break;
+	case DEVICE_EVENT_PROGRESS:
+		progress->current += value;
+		break;
+	default:
+		return;
+	}
+
+	assert (progress->maximum != 0);
+	assert (progress->maximum >= progress->current);
+
+	if (progress->callback)
+		progress->callback (event, progress->current, progress->maximum, progress->userdata);
+}
+
+
+void
+progress_set_maximum (device_progress_state_t *progress, unsigned int value)
+{
+	if (progress == NULL)
+		return;
+
+	assert (value <= progress->maximum);
+	assert (value >= progress->current);
+
+	progress->maximum = value;
+}
diff --git a/src/device.h b/src/device.h
index 88af6f6..b908425 100644
--- a/src/device.h
+++ b/src/device.h
@@ -30,12 +30,20 @@ typedef enum device_status_t {
 	DEVICE_STATUS_MEMORY = -7
 } device_status_t;
 
+typedef enum device_event_t {
+	DEVICE_EVENT_WAITING,
+	DEVICE_EVENT_PROGRESS
+} device_event_t;
+
 typedef struct device_t device_t;
 
 typedef int (*dive_callback_t) (const unsigned char *data, unsigned int size, void *userdata);
+typedef void (*progress_callback_t) (device_event_t event, unsigned int current, unsigned int maximum, void *userdata);
 
 device_type_t device_get_type (device_t *device);
 
+device_status_t device_set_progress (device_t *device, progress_callback_t callback, void *userdata);
+
 device_status_t device_handshake (device_t *device, unsigned char data[], unsigned int size);
 
 device_status_t device_version (device_t *device, unsigned char data[], unsigned int size);