Merge pull request #1248 from emersion/assert-all-the-things

Assert all the things!

24 files changed, 313 insertions, 170 deletions

diff --git a/backend/drm/backend.c b/backend/drm/backend.c
index 1df5cdd1..bba79bda 100644
--- a/backend/drm/backend.c
+++ b/backend/drm/backend.c
@@ -15,8 +15,14 @@
 #include "backend/drm/drm.h"
 #include "util/signal.h"
 
+struct wlr_drm_backend *get_drm_backend_from_backend(
+		struct wlr_backend *wlr_backend) {
+	assert(wlr_backend_is_drm(wlr_backend));
+	return (struct wlr_drm_backend *)wlr_backend;
+}
+
 static bool backend_start(struct wlr_backend *backend) {
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)backend;
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
 	scan_drm_connectors(drm);
 	return true;
 }
@@ -26,7 +32,7 @@ static void backend_destroy(struct wlr_backend *backend) {
 		return;
 	}
 
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)backend;
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
 
 	restore_drm_outputs(drm);
 
@@ -50,7 +56,7 @@ static void backend_destroy(struct wlr_backend *backend) {
 
 static struct wlr_renderer *backend_get_renderer(
 		struct wlr_backend *backend) {
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)backend;
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
 
 	if (drm->parent) {
 		return drm->parent->renderer.wlr_rend;
@@ -141,7 +147,9 @@ struct wlr_backend *wlr_drm_backend_create(struct wl_display *display,
 	wl_list_init(&drm->outputs);
 
 	drm->fd = gpu_fd;
-	drm->parent = (struct wlr_drm_backend *)parent;
+	if (parent != NULL) {
+		drm->parent = get_drm_backend_from_backend(parent);
+	}
 
 	drm->drm_invalidated.notify = drm_invalidated;
 	wlr_session_signal_add(session, gpu_fd, &drm->drm_invalidated);
@@ -187,6 +195,6 @@ error_fd:
 }
 
 struct wlr_session *wlr_drm_backend_get_session(struct wlr_backend *backend) {
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)backend;
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
 	return drm->session;
 }
diff --git a/backend/drm/drm.c b/backend/drm/drm.c
index eac3a312..8e7c421d 100644
--- a/backend/drm/drm.c
+++ b/backend/drm/drm.c
@@ -205,16 +205,22 @@ void finish_drm_resources(struct wlr_drm_backend *drm) {
 	free(drm->planes);
 }
 
+static struct wlr_drm_connector *get_drm_connector_from_output(
+		struct wlr_output *wlr_output) {
+	assert(wlr_output_is_drm(wlr_output));
+	return (struct wlr_drm_connector *)wlr_output;
+}
+
 static bool drm_connector_make_current(struct wlr_output *output,
 		int *buffer_age) {
-	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
 	return make_drm_surface_current(&conn->crtc->primary->surf, buffer_age);
 }
 
 static bool drm_connector_swap_buffers(struct wlr_output *output,
 		pixman_region32_t *damage) {
-	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(output->backend);
 	if (!drm->session->active) {
 		return false;
 	}
@@ -254,8 +260,8 @@ static void fill_empty_gamma_table(uint32_t size,
 }
 
 static uint32_t drm_connector_get_gamma_size(struct wlr_output *output) {
-	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(output->backend);
 
 	if (conn->crtc) {
 		return drm->iface->crtc_get_gamma_size(drm, conn->crtc);
@@ -266,8 +272,8 @@ static uint32_t drm_connector_get_gamma_size(struct wlr_output *output) {
 
 static bool drm_connector_set_gamma(struct wlr_output *output,
 		uint32_t size, uint16_t *r, uint16_t *g, uint16_t *b) {
-	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(output->backend);
 
 	if (!conn->crtc) {
 		return false;
@@ -297,8 +303,8 @@ static bool drm_connector_set_gamma(struct wlr_output *output,
 
 static bool drm_connector_export_dmabuf(struct wlr_output *output,
 		struct wlr_dmabuf_attributes *attribs) {
-	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(output->backend);
 
 	if (!drm->session->active) {
 		return false;
@@ -321,7 +327,8 @@ static void drm_connector_start_renderer(struct wlr_drm_connector *conn) {
 
 	wlr_log(WLR_DEBUG, "Starting renderer on output '%s'", conn->output.name);
 
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)conn->output.backend;
+	struct wlr_drm_backend *drm =
+		get_drm_backend_from_backend(conn->output.backend);
 	struct wlr_drm_crtc *crtc = conn->crtc;
 	if (!crtc) {
 		return;
@@ -361,8 +368,8 @@ static void attempt_enable_needs_modeset(struct wlr_drm_backend *drm) {
 }
 
 bool enable_drm_connector(struct wlr_output *output, bool enable) {
-	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(output->backend);
 	if (conn->state != WLR_DRM_CONN_CONNECTED
 			&& conn->state != WLR_DRM_CONN_NEEDS_MODESET) {
 		return false;
@@ -456,8 +463,8 @@ static void drm_connector_cleanup(struct wlr_drm_connector *conn);
 
 static bool drm_connector_set_mode(struct wlr_output *output,
 		struct wlr_output_mode *mode) {
-	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(output->backend);
 	if (conn->crtc == NULL) {
 		// Maybe we can steal a CRTC from a disabled output
 		realloc_crtcs(drm, NULL);
@@ -496,7 +503,7 @@ static bool drm_connector_set_mode(struct wlr_output *output,
 
 bool wlr_drm_connector_add_mode(struct wlr_output *output,
 		const drmModeModeInfo *modeinfo) {
-	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
 
 	assert(modeinfo);
 	if (modeinfo->type != DRM_MODE_TYPE_USERDEF) {
@@ -528,10 +535,10 @@ static void drm_connector_transform(struct wlr_output *output,
 
 static bool drm_connector_set_cursor(struct wlr_output *output,
 		struct wlr_texture *texture, int32_t scale,
-		enum wl_output_transform transform, int32_t hotspot_x, int32_t hotspot_y,
-		bool update_texture) {
-	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
+		enum wl_output_transform transform,
+		int32_t hotspot_x, int32_t hotspot_y, bool update_texture) {
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(output->backend);
 
 	struct wlr_drm_crtc *crtc = conn->crtc;
 	if (!crtc) {
@@ -664,8 +671,8 @@ static bool drm_connector_set_cursor(struct wlr_output *output,
 
 static bool drm_connector_move_cursor(struct wlr_output *output,
 		int x, int y) {
-	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(output->backend);
 	if (!conn->crtc) {
 		return false;
 	}
@@ -700,7 +707,7 @@ static bool drm_connector_move_cursor(struct wlr_output *output,
 }
 
 static void drm_connector_destroy(struct wlr_output *output) {
-	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
+	struct wlr_drm_connector *conn = get_drm_connector_from_output(output);
 	drm_connector_cleanup(conn);
 	wl_event_source_remove(conn->retry_pageflip);
 	wl_list_remove(&conn->link);
@@ -742,7 +749,8 @@ static const int32_t subpixel_map[] = {
 };
 
 static void dealloc_crtc(struct wlr_drm_connector *conn) {
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)conn->output.backend;
+	struct wlr_drm_backend *drm =
+		get_drm_backend_from_backend(conn->output.backend);
 	if (conn->crtc == NULL) {
 		return;
 	}
@@ -1121,7 +1129,8 @@ void scan_drm_connectors(struct wlr_drm_backend *drm) {
 static void page_flip_handler(int fd, unsigned seq,
 		unsigned tv_sec, unsigned tv_usec, void *user) {
 	struct wlr_drm_connector *conn = user;
-	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)conn->output.backend;
+	struct wlr_drm_backend *drm =
+		get_drm_backend_from_backend(conn->output.backend);
 
 	conn->pageflip_pending = false;
 	if (conn->state != WLR_DRM_CONN_CONNECTED || conn->crtc == NULL) {
diff --git a/backend/headless/backend.c b/backend/headless/backend.c
index 0138166d..cbc158f3 100644
--- a/backend/headless/backend.c
+++ b/backend/headless/backend.c
@@ -1,4 +1,4 @@
-#include "util/signal.h"
+#include <assert.h>
 #include <stdlib.h>
 #include <wlr/interfaces/wlr_input_device.h>
 #include <wlr/interfaces/wlr_output.h>
@@ -7,10 +7,17 @@
 #include <wlr/util/log.h>
 #include "backend/headless.h"
 #include "glapi.h"
+#include "util/signal.h"
+
+struct wlr_headless_backend *headless_backend_from_backend(
+		struct wlr_backend *wlr_backend) {
+	assert(wlr_backend_is_headless(wlr_backend));
+	return (struct wlr_headless_backend *)wlr_backend;
+}
 
 static bool backend_start(struct wlr_backend *wlr_backend) {
 	struct wlr_headless_backend *backend =
-		(struct wlr_headless_backend *)wlr_backend;
+		headless_backend_from_backend(wlr_backend);
 	wlr_log(WLR_INFO, "Starting headless backend");
 
 	struct wlr_headless_output *output;
@@ -34,7 +41,7 @@ static bool backend_start(struct wlr_backend *wlr_backend) {
 
 static void backend_destroy(struct wlr_backend *wlr_backend) {
 	struct wlr_headless_backend *backend =
-		(struct wlr_headless_backend *)wlr_backend;
+		headless_backend_from_backend(wlr_backend);
 	if (!wlr_backend) {
 		return;
 	}
@@ -62,7 +69,7 @@ static void backend_destroy(struct wlr_backend *wlr_backend) {
 static struct wlr_renderer *backend_get_renderer(
 		struct wlr_backend *wlr_backend) {
 	struct wlr_headless_backend *backend =
-		(struct wlr_headless_backend *)wlr_backend;
+		headless_backend_from_backend(wlr_backend);
 	return backend->renderer;
 }
 
@@ -107,9 +114,8 @@ struct wlr_backend *wlr_headless_backend_create(struct wl_display *display,
 		create_renderer_func = wlr_renderer_autocreate;
 	}
 
-	backend->renderer = create_renderer_func(&backend->egl, EGL_PLATFORM_SURFACELESS_MESA,
-		NULL, (EGLint*)config_attribs, 0);
-
+	backend->renderer = create_renderer_func(&backend->egl,
+		EGL_PLATFORM_SURFACELESS_MESA, NULL, (EGLint*)config_attribs, 0);
 	if (!backend->renderer) {
 		wlr_log(WLR_ERROR, "Failed to create renderer");
 		free(backend);
diff --git a/backend/headless/input_device.c b/backend/headless/input_device.c
index a2474aeb..ba251dd7 100644
--- a/backend/headless/input_device.c
+++ b/backend/headless/input_device.c
@@ -1,3 +1,4 @@
+#include <assert.h>
 #include <stdlib.h>
 #include <wlr/interfaces/wlr_input_device.h>
 #include <wlr/interfaces/wlr_keyboard.h>
@@ -18,7 +19,7 @@ bool wlr_input_device_is_headless(struct wlr_input_device *wlr_dev) {
 struct wlr_input_device *wlr_headless_add_input_device(
 		struct wlr_backend *wlr_backend, enum wlr_input_device_type type) {
 	struct wlr_headless_backend *backend =
-		(struct wlr_headless_backend *)wlr_backend;
+		headless_backend_from_backend(wlr_backend);
 
 	struct wlr_headless_input_device *device =
 		calloc(1, sizeof(struct wlr_headless_input_device));
diff --git a/backend/headless/output.c b/backend/headless/output.c
index 24fc3bfd..143900d4 100644
--- a/backend/headless/output.c
+++ b/backend/headless/output.c
@@ -1,3 +1,4 @@
+#include <assert.h>
 #include <EGL/egl.h>
 #include <EGL/eglext.h>
 #include <stdlib.h>
@@ -7,6 +8,12 @@
 #include "backend/headless.h"
 #include "util/signal.h"
 
+static struct wlr_headless_output *headless_output_from_output(
+		struct wlr_output *wlr_output) {
+	assert(wlr_output_is_headless(wlr_output));
+	return (struct wlr_headless_output *)wlr_output;
+}
+
 static EGLSurface egl_create_surface(struct wlr_egl *egl, unsigned int width,
 		unsigned int height) {
 	EGLint attribs[] = {EGL_WIDTH, width, EGL_HEIGHT, height, EGL_NONE};
@@ -22,7 +29,7 @@ static EGLSurface egl_create_surface(struct wlr_egl *egl, unsigned int width,
 static bool output_set_custom_mode(struct wlr_output *wlr_output, int32_t width,
 		int32_t height, int32_t refresh) {
 	struct wlr_headless_output *output =
-		(struct wlr_headless_output *)wlr_output;
+		headless_output_from_output(wlr_output);
 	struct wlr_headless_backend *backend = output->backend;
 
 	if (refresh <= 0) {
@@ -47,13 +54,13 @@ static bool output_set_custom_mode(struct wlr_output *wlr_output, int32_t width,
 static void output_transform(struct wlr_output *wlr_output,
 		enum wl_output_transform transform) {
 	struct wlr_headless_output *output =
-		(struct wlr_headless_output *)wlr_output;
+		headless_output_from_output(wlr_output);
 	output->wlr_output.transform = transform;
 }
 
 static bool output_make_current(struct wlr_output *wlr_output, int *buffer_age) {
 	struct wlr_headless_output *output =
-		(struct wlr_headless_output *)wlr_output;
+		headless_output_from_output(wlr_output);
 	return wlr_egl_make_current(&output->backend->egl, output->egl_surface,
 		buffer_age);
 }
@@ -65,7 +72,7 @@ static bool output_swap_buffers(struct wlr_output *wlr_output,
 
 static void output_destroy(struct wlr_output *wlr_output) {
 	struct wlr_headless_output *output =
-		(struct wlr_headless_output *)wlr_output;
+		headless_output_from_output(wlr_output);
 
 	wl_list_remove(&output->link);
 
@@ -97,7 +104,7 @@ static int signal_frame(void *data) {
 struct wlr_output *wlr_headless_add_output(struct wlr_backend *wlr_backend,
 		unsigned int width, unsigned int height) {
 	struct wlr_headless_backend *backend =
-		(struct wlr_headless_backend *)wlr_backend;
+		headless_backend_from_backend(wlr_backend);
 
 	struct wlr_headless_output *output =
 		calloc(1, sizeof(struct wlr_headless_output));
diff --git a/backend/libinput/backend.c b/backend/libinput/backend.c
index 19dc779d..8106af00 100644
--- a/backend/libinput/backend.c
+++ b/backend/libinput/backend.c
@@ -7,6 +7,12 @@
 #include "backend/libinput.h"
 #include "util/signal.h"
 
+static struct wlr_libinput_backend *get_libinput_backend_from_backend(
+		struct wlr_backend *wlr_backend) {
+	assert(wlr_backend_is_libinput(wlr_backend));
+	return (struct wlr_libinput_backend *)wlr_backend;
+}
+
 static int libinput_open_restricted(const char *path,
 		int flags, void *_backend) {
 	struct wlr_libinput_backend *backend = _backend;
@@ -43,9 +49,9 @@ static void log_libinput(struct libinput *libinput_context,
 	_wlr_vlog(WLR_ERROR, fmt, args);
 }
 
-static bool backend_start(struct wlr_backend *_backend) {
+static bool backend_start(struct wlr_backend *wlr_backend) {
 	struct wlr_libinput_backend *backend =
-		(struct wlr_libinput_backend *)_backend;
+		get_libinput_backend_from_backend(wlr_backend);
 	wlr_log(WLR_DEBUG, "Initializing libinput");
 
 	backend->libinput_context = libinput_udev_create_context(&libinput_impl,
@@ -101,7 +107,7 @@ static void backend_destroy(struct wlr_backend *wlr_backend) {
 		return;
 	}
 	struct wlr_libinput_backend *backend =
-		(struct wlr_libinput_backend *)wlr_backend;
+		get_libinput_backend_from_backend(wlr_backend);
 
 	for (size_t i = 0; i < backend->wlr_device_lists.length; i++) {
 		struct wl_list *wlr_devices = backend->wlr_device_lists.items[i];
@@ -158,9 +164,8 @@ static void handle_display_destroy(struct wl_listener *listener, void *data) {
 
 struct wlr_backend *wlr_libinput_backend_create(struct wl_display *display,
 		struct wlr_session *session) {
-	assert(display && session);
-
-	struct wlr_libinput_backend *backend = calloc(1, sizeof(struct wlr_libinput_backend));
+	struct wlr_libinput_backend *backend =
+		calloc(1, sizeof(struct wlr_libinput_backend));
 	if (!backend) {
 		wlr_log(WLR_ERROR, "Allocation failed: %s", strerror(errno));
 		return NULL;
@@ -187,8 +192,10 @@ error_backend:
 	return NULL;
 }
 
-struct libinput_device *wlr_libinput_get_device_handle(struct wlr_input_device *_dev) {
-	struct wlr_libinput_input_device *dev = (struct wlr_libinput_input_device *)_dev;
+struct libinput_device *wlr_libinput_get_device_handle(
+		struct wlr_input_device *wlr_dev) {
+	struct wlr_libinput_input_device *dev =
+		(struct wlr_libinput_input_device *)wlr_dev;
 	return dev->handle;
 }
 
diff --git a/backend/libinput/events.c b/backend/libinput/events.c
index 0548e502..9ce62d6f 100644
--- a/backend/libinput/events.c
+++ b/backend/libinput/events.c
@@ -9,6 +9,12 @@
 #include "backend/libinput.h"
 #include "util/signal.h"
 
+struct wlr_libinput_input_device *get_libinput_device_from_device(
+		struct wlr_input_device *wlr_dev) {
+	assert(wlr_input_device_is_libinput(wlr_dev));
+	return (struct wlr_libinput_input_device *)wlr_dev;
+}
+
 struct wlr_input_device *get_appropriate_device(
 		enum wlr_input_device_type desired_type,
 		struct libinput_device *libinput_dev) {
@@ -25,8 +31,9 @@ struct wlr_input_device *get_appropriate_device(
 	return NULL;
 }
 
-static void input_device_destroy(struct wlr_input_device *_dev) {
-	struct wlr_libinput_input_device *dev = (struct wlr_libinput_input_device *)_dev;
+static void input_device_destroy(struct wlr_input_device *wlr_dev) {
+	struct wlr_libinput_input_device *dev =
+		get_libinput_device_from_device(wlr_dev);
 	libinput_device_unref(dev->handle);
 	wl_list_remove(&dev->wlr_input_device.link);
 	free(dev);
@@ -37,16 +44,18 @@ static const struct wlr_input_device_impl input_device_impl = {
 };
 
 static struct wlr_input_device *allocate_device(
-		struct wlr_libinput_backend *backend, struct libinput_device *libinput_dev,
-		struct wl_list *wlr_devices, enum wlr_input_device_type type) {
+		struct wlr_libinput_backend *backend,
+		struct libinput_device *libinput_dev, struct wl_list *wlr_devices,
+		enum wlr_input_device_type type) {
 	int vendor = libinput_device_get_id_vendor(libinput_dev);
 	int product = libinput_device_get_id_product(libinput_dev);
 	const char *name = libinput_device_get_name(libinput_dev);
-	struct wlr_libinput_input_device *wlr_libinput_dev;
-	if (!(wlr_libinput_dev = calloc(1, sizeof(struct wlr_libinput_input_device)))) {
+	struct wlr_libinput_input_device *dev =
+		calloc(1, sizeof(struct wlr_libinput_input_device));
+	if (dev == NULL) {
 		return NULL;
 	}
-	struct wlr_input_device *wlr_dev = &wlr_libinput_dev->wlr_input_device;
+	struct wlr_input_device *wlr_dev = &dev->wlr_input_device;
 	libinput_device_get_size(libinput_dev,
 			&wlr_dev->width_mm, &wlr_dev->height_mm);
 	const char *output_name = libinput_device_get_output_name(libinput_dev);
@@ -54,7 +63,7 @@ static struct wlr_input_device *allocate_device(
 		wlr_dev->output_name = strdup(output_name);
 	}
 	wl_list_insert(wlr_devices, &wlr_dev->link);
-	wlr_libinput_dev->handle = libinput_dev;
+	dev->handle = libinput_dev;
 	libinput_device_ref(libinput_dev);
 	wlr_input_device_init(wlr_dev, type, &input_device_impl,
 			name, vendor, product);
@@ -62,12 +71,11 @@ static struct wlr_input_device *allocate_device(
 }
 
 bool wlr_input_device_is_libinput(struct wlr_input_device *wlr_dev) {
-        return wlr_dev->impl == &input_device_impl;
+	return wlr_dev->impl == &input_device_impl;
 }
 
 static void handle_device_added(struct wlr_libinput_backend *backend,
 		struct libinput_device *libinput_dev) {
-	assert(backend && libinput_dev);
 	/*
 	 * Note: the wlr API exposes only devices with a single capability, because
 	 * that meshes better with how Wayland does things and is a bit simpler.
@@ -85,7 +93,8 @@ static void handle_device_added(struct wlr_libinput_backend *backend,
 	wl_list_init(wlr_devices);
 	wlr_log(WLR_DEBUG, "Added %s [%d:%d]", name, vendor, product);
 
-	if (libinput_device_has_capability(libinput_dev, LIBINPUT_DEVICE_CAP_KEYBOARD)) {
+	if (libinput_device_has_capability(
+			libinput_dev, LIBINPUT_DEVICE_CAP_KEYBOARD)) {
 		struct wlr_input_device *wlr_dev = allocate_device(backend,
 				libinput_dev, wlr_devices, WLR_INPUT_DEVICE_KEYBOARD);
 		if (!wlr_dev) {
@@ -98,7 +107,8 @@ static void handle_device_added(struct wlr_libinput_backend *backend,
 		}
 		wlr_signal_emit_safe(&backend->backend.events.new_input, wlr_dev);
 	}
-	if (libinput_device_has_capability(libinput_dev, LIBINPUT_DEVICE_CAP_POINTER)) {
+	if (libinput_device_has_capability(
+			libinput_dev, LIBINPUT_DEVICE_CAP_POINTER)) {
 		struct wlr_input_device *wlr_dev = allocate_device(backend,
 				libinput_dev, wlr_devices, WLR_INPUT_DEVICE_POINTER);
 		if (!wlr_dev) {
@@ -111,7 +121,8 @@ static void handle_device_added(struct wlr_libinput_backend *backend,
 		}
 		wlr_signal_emit_safe(&backend->backend.events.new_input, wlr_dev);
 	}
-	if (libinput_device_has_capability(libinput_dev, LIBINPUT_DEVICE_CAP_TOUCH)) {
+	if (libinput_device_has_capability(
+			libinput_dev, LIBINPUT_DEVICE_CAP_TOUCH)) {
 		struct wlr_input_device *wlr_dev = allocate_device(backend,
 				libinput_dev, wlr_devices, WLR_INPUT_DEVICE_TOUCH);
 		if (!wlr_dev) {
@@ -124,7 +135,8 @@ static void handle_device_added(struct wlr_libinput_backend *backend,
 		}
 		wlr_signal_emit_safe(&backend->backend.events.new_input, wlr_dev);
 	}
-	if (libinput_device_has_capability(libinput_dev, LIBINPUT_DEVICE_CAP_TABLET_TOOL)) {
+	if (libinput_device_has_capability(libinput_dev,
+			LIBINPUT_DEVICE_CAP_TABLET_TOOL)) {
 		struct wlr_input_device *wlr_dev = allocate_device(backend,
 				libinput_dev, wlr_devices, WLR_INPUT_DEVICE_TABLET_TOOL);
 		if (!wlr_dev) {
@@ -137,7 +149,8 @@ static void handle_device_added(struct wlr_libinput_backend *backend,
 		}
 		wlr_signal_emit_safe(&backend->backend.events.new_input, wlr_dev);
 	}
-	if (libinput_device_has_capability(libinput_dev, LIBINPUT_DEVICE_CAP_TABLET_PAD)) {
+	if (libinput_device_has_capability(
+			libinput_dev, LIBINPUT_DEVICE_CAP_TABLET_PAD)) {
 		struct wlr_input_device *wlr_dev = allocate_device(backend,
 				libinput_dev, wlr_devices, WLR_INPUT_DEVICE_TABLET_PAD);
 		if (!wlr_dev) {
@@ -150,14 +163,16 @@ static void handle_device_added(struct wlr_libinput_backend *backend,
 		}
 		wlr_signal_emit_safe(&backend->backend.events.new_input, wlr_dev);
 	}
-	if (libinput_device_has_capability(libinput_dev, LIBINPUT_DEVICE_CAP_GESTURE)) {
+	if (libinput_device_has_capability(
+			libinput_dev, LIBINPUT_DEVICE_CAP_GESTURE)) {
 		// TODO
 	}
-	if (libinput_device_has_capability(libinput_dev, LIBINPUT_DEVICE_CAP_SWITCH)) {
+	if (libinput_device_has_capability(
+			libinput_dev, LIBINPUT_DEVICE_CAP_SWITCH)) {
 		// TODO
 	}
 
-	if (wl_list_length(wlr_devices) > 0) {
+	if (!wl_list_empty(wlr_devices)) {
 		libinput_device_set_user_data(libinput_dev, wlr_devices);
 		wlr_list_push(&backend->wlr_device_lists, wlr_devices);
 	} else {
@@ -199,7 +214,6 @@ static void handle_device_removed(struct wlr_libinput_backend *backend,
 
 void handle_libinput_event(struct wlr_libinput_backend *backend,
 		struct libinput_event *event) {
-	assert(backend && event);
 	struct libinput_device *libinput_dev = libinput_event_get_device(event);
 	enum libinput_event_type event_type = libinput_event_get_type(event);
 	switch (event_type) {
diff --git a/backend/libinput/keyboard.c b/backend/libinput/keyboard.c
index d0059e06..93605e77 100644
--- a/backend/libinput/keyboard.c
+++ b/backend/libinput/keyboard.c
@@ -12,35 +12,43 @@ struct wlr_libinput_keyboard {
 	struct libinput_device *libinput_dev;
 };
 
+static const struct wlr_keyboard_impl impl;
+
+static struct wlr_libinput_keyboard *get_libinput_keyboard_from_keyboard(
+		struct wlr_keyboard *wlr_kb) {
+	assert(wlr_kb->impl == &impl);
+	return (struct wlr_libinput_keyboard *)wlr_kb;
+}
+
 static void keyboard_set_leds(struct wlr_keyboard *wlr_kb, uint32_t leds) {
-	struct wlr_libinput_keyboard *wlr_libinput_kb =
-		(struct wlr_libinput_keyboard *)wlr_kb;
-	libinput_device_led_update(wlr_libinput_kb->libinput_dev, leds);
+	struct wlr_libinput_keyboard *kb =
+		get_libinput_keyboard_from_keyboard(wlr_kb);
+	libinput_device_led_update(kb->libinput_dev, leds);
 }
 
 static void keyboard_destroy(struct wlr_keyboard *wlr_kb) {
-	struct wlr_libinput_keyboard *wlr_libinput_kb =
-		(struct wlr_libinput_keyboard *)wlr_kb;
-	libinput_device_unref(wlr_libinput_kb->libinput_dev);
-	free(wlr_libinput_kb);
+	struct wlr_libinput_keyboard *kb =
+		get_libinput_keyboard_from_keyboard(wlr_kb);
+	libinput_device_unref(kb->libinput_dev);
+	free(kb);
 }
 
-struct wlr_keyboard_impl impl = {
+static const struct wlr_keyboard_impl impl = {
 	.destroy = keyboard_destroy,
 	.led_update = keyboard_set_leds
 };
 
 struct wlr_keyboard *create_libinput_keyboard(
 		struct libinput_device *libinput_dev) {
-	assert(libinput_dev);
-	struct wlr_libinput_keyboard *wlr_libinput_kb;
-	if (!(wlr_libinput_kb= calloc(1, sizeof(struct wlr_libinput_keyboard)))) {
+	struct wlr_libinput_keyboard *kb =
+		calloc(1, sizeof(struct wlr_libinput_keyboard));
+	if (kb == NULL) {
 		return NULL;
 	}
-	wlr_libinput_kb->libinput_dev = libinput_dev;
+	kb->libinput_dev = libinput_dev;
 	libinput_device_ref(libinput_dev);
 	libinput_device_led_update(libinput_dev, 0);
-	struct wlr_keyboard *wlr_kb = &wlr_libinput_kb->wlr_keyboard;
+	struct wlr_keyboard *wlr_kb = &kb->wlr_keyboard;
 	wlr_keyboard_init(wlr_kb, &impl);
 	return wlr_kb;
 }
@@ -50,7 +58,8 @@ void handle_keyboard_key(struct libinput_event *event,
 	struct wlr_input_device *wlr_dev =
 		get_appropriate_device(WLR_INPUT_DEVICE_KEYBOARD, libinput_dev);
 	if (!wlr_dev) {
-		wlr_log(WLR_DEBUG, "Got a keyboard event for a device with no keyboards?");
+		wlr_log(WLR_DEBUG,
+			"Got a keyboard event for a device with no keyboards?");
 		return;
 	}
 	struct libinput_event_keyboard *kbevent =
diff --git a/backend/libinput/tablet_pad.c b/backend/libinput/tablet_pad.c
index 0642f925..b053b9a0 100644
--- a/backend/libinput/tablet_pad.c
+++ b/backend/libinput/tablet_pad.c
@@ -69,7 +69,8 @@ static void add_pad_group_from_libinput(struct wlr_tablet_pad *pad,
 struct wlr_tablet_pad *create_libinput_tablet_pad(
 		struct libinput_device *libinput_dev) {
 	assert(libinput_dev);
-	struct wlr_tablet_pad *wlr_tablet_pad = calloc(1, sizeof(struct wlr_tablet_pad));
+	struct wlr_tablet_pad *wlr_tablet_pad =
+		calloc(1, sizeof(struct wlr_tablet_pad));
 	if (!wlr_tablet_pad) {
 		wlr_log(WLR_ERROR, "Unable to allocate wlr_tablet_pad");
 		return NULL;
@@ -101,7 +102,8 @@ void handle_tablet_pad_button(struct libinput_event *event,
 	struct wlr_input_device *wlr_dev =
 		get_appropriate_device(WLR_INPUT_DEVICE_TABLET_PAD, libinput_dev);
 	if (!wlr_dev) {
-		wlr_log(WLR_DEBUG, "Got a tablet pad event for a device with no tablet pad?");
+		wlr_log(WLR_DEBUG,
+			"Got a tablet pad event for a device with no tablet pad?");
 		return;
 	}
 	struct libinput_event_tablet_pad *pevent =
@@ -129,7 +131,8 @@ void handle_tablet_pad_ring(struct libinput_event *event,
 	struct wlr_input_device *wlr_dev =
 		get_appropriate_device(WLR_INPUT_DEVICE_TABLET_PAD, libinput_dev);
 	if (!wlr_dev) {
-		wlr_log(WLR_DEBUG, "Got a tablet pad event for a device with no tablet pad?");
+		wlr_log(WLR_DEBUG,
+			"Got a tablet pad event for a device with no tablet pad?");
 		return;
 	}
 	struct libinput_event_tablet_pad *pevent =
@@ -156,7 +159,8 @@ void handle_tablet_pad_strip(struct libinput_event *event,
 	struct wlr_input_device *wlr_dev =
 		get_appropriate_device(WLR_INPUT_DEVICE_TABLET_PAD, libinput_dev);
 	if (!wlr_dev) {
-		wlr_log(WLR_DEBUG, "Got a tablet pad event for a device with no tablet pad?");
+		wlr_log(WLR_DEBUG,
+			"Got a tablet pad event for a device with no tablet pad?");
 		return;
 	}
 	struct libinput_event_tablet_pad *pevent =
diff --git a/backend/libinput/tablet_tool.c b/backend/libinput/tablet_tool.c
index adfc6221..4e87b700 100644
--- a/backend/libinput/tablet_tool.c
+++ b/backend/libinput/tablet_tool.c
@@ -156,7 +156,8 @@ static struct wlr_libinput_tablet_tool *get_wlr_tablet_tool(
 static void ensure_tool_reference(struct wlr_libinput_tablet_tool *tool,
 		struct wlr_tablet *wlr_dev) {
 	assert(tablet_is_libinput(wlr_dev));
-	struct wlr_libinput_tablet *tablet = wl_container_of(wlr_dev, tablet, wlr_tablet);
+	struct wlr_libinput_tablet *tablet =
+		wl_container_of(wlr_dev, tablet, wlr_tablet);
 
 	struct tablet_tool_list_elem *pos;
 	wl_list_for_each(pos, &tablet->tools, link) {
@@ -188,7 +189,8 @@ void handle_tablet_tool_axis(struct libinput_event *event,
 	struct wlr_input_device *wlr_dev =
 		get_appropriate_device(WLR_INPUT_DEVICE_TABLET_TOOL, libinput_dev);
 	if (!wlr_dev) {
-		wlr_log(WLR_DEBUG, "Got a tablet tool event for a device with no tablet tools?");
+		wlr_log(WLR_DEBUG,
+			"Got a tablet tool event for a device with no tablet tools?");
 		return;
 	}
 	struct libinput_event_tablet_tool *tevent =
@@ -248,7 +250,8 @@ void handle_tablet_tool_proximity(struct libinput_event *event,
 	struct wlr_input_device *wlr_dev =
 		get_appropriate_device(WLR_INPUT_DEVICE_TABLET_TOOL, libinput_dev);
 	if (!wlr_dev) {
-		wlr_log(WLR_DEBUG, "Got a tablet tool event for a device with no tablet tools?");
+		wlr_log(WLR_DEBUG,
+			"Got a tablet tool event for a device with no tablet tools?");
 		return;
 	}
 	struct libinput_event_tablet_tool *tevent =
@@ -272,14 +275,16 @@ void handle_tablet_tool_proximity(struct libinput_event *event,
 	}
 	wlr_signal_emit_safe(&wlr_dev->tablet->events.proximity, &wlr_event);
 
-	if (libinput_event_tablet_tool_get_proximity_state(tevent) == LIBINPUT_TABLET_TOOL_PROXIMITY_STATE_IN) {
+	if (libinput_event_tablet_tool_get_proximity_state(tevent) ==
+			LIBINPUT_TABLET_TOOL_PROXIMITY_STATE_IN) {
 		handle_tablet_tool_axis(event, libinput_dev);
 	}
 
 	// If the tool is not unique, libinput will not find it again after the
 	// proximity out, so we should destroy it
 	if (!tool->unique &&
-			libinput_event_tablet_tool_get_proximity_state(tevent) == LIBINPUT_TABLET_TOOL_PROXIMITY_STATE_OUT) {
+			libinput_event_tablet_tool_get_proximity_state(tevent) ==
+			LIBINPUT_TABLET_TOOL_PROXIMITY_STATE_OUT) {
 		// The tool isn't unique, it can't be on multiple tablets
 		assert(tool->pad_refs == 1);
 		assert(tablet_is_libinput(wlr_dev->tablet));
@@ -305,7 +310,8 @@ void handle_tablet_tool_tip(struct libinput_event *event,
 	struct wlr_input_device *wlr_dev =
 		get_appropriate_device(WLR_INPUT_DEVICE_TABLET_TOOL, libinput_dev);
 	if (!wlr_dev) {
-		wlr_log(WLR_DEBUG, "Got a tablet tool event for a device with no tablet tools?");
+		wlr_log(WLR_DEBUG,
+			"Got a tablet tool event for a device with no tablet tools?");
 		return;
 	}
 	handle_tablet_tool_axis(event, libinput_dev);
@@ -336,7 +342,8 @@ void handle_tablet_tool_button(struct libinput_event *event,
 	struct wlr_input_device *wlr_dev =
 		get_appropriate_device(WLR_INPUT_DEVICE_TABLET_TOOL, libinput_dev);
 	if (!wlr_dev) {
-		wlr_log(WLR_DEBUG, "Got a tablet tool event for a device with no tablet tools?");
+		wlr_log(WLR_DEBUG,
+			"Got a tablet tool event for a device with no tablet tools?");
 		return;
 	}
 	handle_tablet_tool_axis(event, libinput_dev);
diff --git a/backend/multi/backend.c b/backend/multi/backend.c
index e0038955..1665bf28 100644
--- a/backend/multi/backend.c
+++ b/backend/multi/backend.c
@@ -17,8 +17,14 @@ struct subbackend_state {
 	struct wl_list link;
 };
 
+static struct wlr_multi_backend *multi_backend_from_backend(
+		struct wlr_backend *wlr_backend) {
+	assert(wlr_backend_is_multi(wlr_backend));
+	return (struct wlr_multi_backend *)wlr_backend;
+}
+
 static bool multi_backend_start(struct wlr_backend *wlr_backend) {
-	struct wlr_multi_backend *backend = (struct wlr_multi_backend *)wlr_backend;
+	struct wlr_multi_backend *backend = multi_backend_from_backend(wlr_backend);
 	struct subbackend_state *sub;
 	wl_list_for_each(sub, &backend->backends, link) {
 		if (!wlr_backend_start(sub->backend)) {
@@ -38,7 +44,7 @@ static void subbackend_state_destroy(struct subbackend_state *sub) {
 }
 
 static void multi_backend_destroy(struct wlr_backend *wlr_backend) {
-	struct wlr_multi_backend *backend = (struct wlr_multi_backend *)wlr_backend;
+	struct wlr_multi_backend *backend = multi_backend_from_backend(wlr_backend);
 
 	wl_list_remove(&backend->display_destroy.link);
 
@@ -54,7 +60,8 @@ static void multi_backend_destroy(struct wlr_backend *wlr_backend) {
 
 static struct wlr_renderer *multi_backend_get_renderer(
 		struct wlr_backend *backend) {
-	struct wlr_multi_backend *multi = (struct wlr_multi_backend *)backend;
+	struct wlr_multi_backend *multi = multi_backend_from_backend(backend);
+
 	struct subbackend_state *sub;
 	wl_list_for_each(sub, &multi->backends, link) {
 		struct wlr_renderer *rend = wlr_backend_get_renderer(sub->backend);
@@ -132,8 +139,7 @@ static struct subbackend_state *multi_backend_get_subbackend(struct wlr_multi_ba
 
 bool wlr_multi_backend_add(struct wlr_backend *_multi,
 		struct wlr_backend *backend) {
-	assert(wlr_backend_is_multi(_multi));
-	struct wlr_multi_backend *multi = (struct wlr_multi_backend *)_multi;
+	struct wlr_multi_backend *multi = multi_backend_from_backend(_multi);
 
 	if (multi_backend_get_subbackend(multi, backend)) {
 		// already added
@@ -174,8 +180,7 @@ bool wlr_multi_backend_add(struct wlr_backend *_multi,
 
 void wlr_multi_backend_remove(struct wlr_backend *_multi,
 		struct wlr_backend *backend) {
-	assert(wlr_backend_is_multi(_multi));
-	struct wlr_multi_backend *multi = (struct wlr_multi_backend *)_multi;
+	struct wlr_multi_backend *multi = multi_backend_from_backend(_multi);
 
 	struct subbackend_state *sub =
 		multi_backend_get_subbackend(multi, backend);
@@ -187,9 +192,7 @@ void wlr_multi_backend_remove(struct wlr_backend *_multi,
 }
 
 struct wlr_session *wlr_multi_get_session(struct wlr_backend *_backend) {
-	assert(wlr_backend_is_multi(_backend));
-
-	struct wlr_multi_backend *backend = (struct wlr_multi_backend *)_backend;
+	struct wlr_multi_backend *backend = multi_backend_from_backend(_backend);
 	struct subbackend_state *sub;
 	wl_list_for_each(sub, &backend->backends, link) {
 		if (wlr_backend_is_drm(sub->backend)) {
diff --git a/backend/session/direct-freebsd.c b/backend/session/direct-freebsd.c
index cecfb0c1..bce1c871 100644
--- a/backend/session/direct-freebsd.c
+++ b/backend/session/direct-freebsd.c
@@ -1,3 +1,4 @@
+#include <assert.h>
 #include <dev/evdev/input.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -32,8 +33,14 @@ struct direct_session {
 	struct wl_event_source *vt_source;
 };
 
+static struct direct_session *direct_session_from_session(
+		struct wlr_session *base) {
+	assert(base->impl == &session_direct);
+	return (struct direct_session *)base;
+}
+
 static int direct_session_open(struct wlr_session *base, const char *path) {
-	struct direct_session *session = wl_container_of(base, session, base);
+	struct direct_session *session = direct_session_from_session(base);
 
 	int fd = direct_ipc_open(session->sock, path);
 	if (fd < 0) {
@@ -46,7 +53,7 @@ static int direct_session_open(struct wlr_session *base, const char *path) {
 }
 
 static void direct_session_close(struct wlr_session *base, int fd) {
-	struct direct_session *session = wl_container_of(base, session, base);
+	struct direct_session *session = direct_session_from_session(base);
 
 	int ev;
 	struct drm_version dv = {0};
@@ -60,12 +67,12 @@ static void direct_session_close(struct wlr_session *base, int fd) {
 }
 
 static bool direct_change_vt(struct wlr_session *base, unsigned vt) {
-	struct direct_session *session = wl_container_of(base, session, base);
+	struct direct_session *session = direct_session_from_session(base);
 	return ioctl(session->tty_fd, VT_ACTIVATE, (int)vt) == 0;
 }
 
 static void direct_session_destroy(struct wlr_session *base) {
-	struct direct_session *session = wl_container_of(base, session, base);
+	struct direct_session *session = direct_session_from_session(base);
 	struct vt_mode mode = {
 		.mode = VT_AUTO,
 	};
@@ -157,7 +164,8 @@ static bool setup_tty(struct direct_session *session, struct wl_display *display
 	}
 
 	if (ioctl(fd, KDSKBMODE, K_CODE)) {
-		wlr_log_errno(WLR_ERROR, "Failed to set keyboard mode K_CODE on tty %d", tty);
+		wlr_log_errno(WLR_ERROR,
+			"Failed to set keyboard mode K_CODE on tty %d", tty);
 		goto error;
 	}
 
diff --git a/backend/session/direct.c b/backend/session/direct.c
index ed7a0c65..0912cd58 100644
--- a/backend/session/direct.c
+++ b/backend/session/direct.c
@@ -1,4 +1,5 @@
 #define _POSIX_C_SOURCE 200809L
+#include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <linux/input.h>
@@ -33,8 +34,14 @@ struct direct_session {
 	struct wl_event_source *vt_source;
 };
 
+static struct direct_session *direct_session_from_session(
+		struct wlr_session *base) {
+	assert(base->impl == &session_direct);
+	return (struct direct_session *)base;
+}
+
 static int direct_session_open(struct wlr_session *base, const char *path) {
-	struct direct_session *session = wl_container_of(base, session, base);
+	struct direct_session *session = direct_session_from_session(base);
 
 	int fd = direct_ipc_open(session->sock, path);
 	if (fd < 0) {
@@ -57,7 +64,7 @@ static int direct_session_open(struct wlr_session *base, const char *path) {
 }
 
 static void direct_session_close(struct wlr_session *base, int fd) {
-	struct direct_session *session = wl_container_of(base, session, base);
+	struct direct_session *session = direct_session_from_session(base);
 
 	struct stat st;
 	if (fstat(fd, &st) < 0) {
@@ -76,7 +83,7 @@ static void direct_session_close(struct wlr_session *base, int fd) {
 }
 
 static bool direct_change_vt(struct wlr_session *base, unsigned vt) {
-	struct direct_session *session = wl_container_of(base, session, base);
+	struct direct_session *session = direct_session_from_session(base);
 
 	// Only seat0 has VTs associated with it
 	if (strcmp(session->base.seat, "seat0") != 0) {
@@ -87,7 +94,7 @@ static bool direct_change_vt(struct wlr_session *base, unsigned vt) {
 }
 
 static void direct_session_destroy(struct wlr_session *base) {
-	struct direct_session *session = wl_container_of(base, session, base);
+	struct direct_session *session = direct_session_from_session(base);
 
 	if (strcmp(session->base.seat, "seat0") == 0) {
 		struct vt_mode mode = {
diff --git a/backend/session/logind.c b/backend/session/logind.c
index 2f816b95..39143a2f 100644
--- a/backend/session/logind.c
+++ b/backend/session/logind.c
@@ -37,8 +37,14 @@ struct logind_session {
 	char *path;
 };
 
+static struct logind_session *logind_session_from_session(
+		struct wlr_session *base) {
+	assert(base->impl == &session_logind);
+	return (struct logind_session *)base;
+}
+
 static int logind_take_device(struct wlr_session *base, const char *path) {
-	struct logind_session *session = wl_container_of(base, session, base);
+	struct logind_session *session = logind_session_from_session(base);
 
 	int ret;
 	int fd = -1;
@@ -83,7 +89,7 @@ error:
 }
 
 static void logind_release_device(struct wlr_session *base, int fd) {
-	struct logind_session *session = wl_container_of(base, session, base);
+	struct logind_session *session = logind_session_from_session(base);
 
 	int ret;
 	sd_bus_message *msg = NULL;
@@ -108,7 +114,7 @@ static void logind_release_device(struct wlr_session *base, int fd) {
 }
 
 static bool logind_change_vt(struct wlr_session *base, unsigned vt) {
-	struct logind_session *session = wl_container_of(base, session, base);
+	struct logind_session *session = logind_session_from_session(base);
 
 	// Only seat0 has VTs associated with it
 	if (strcmp(session->base.seat, "seat0") != 0) {
@@ -212,7 +218,7 @@ static void release_control(struct logind_session *session) {
 }
 
 static void logind_session_destroy(struct wlr_session *base) {
-	struct logind_session *session = wl_container_of(base, session, base);
+	struct logind_session *session = logind_session_from_session(base);
 
 	release_control(session);
 
diff --git a/backend/wayland/backend.c b/backend/wayland/backend.c
index 506bcd5e..28f61863 100644
--- a/backend/wayland/backend.c
+++ b/backend/wayland/backend.c
@@ -15,6 +15,12 @@
 #include "util/signal.h"
 #include "xdg-shell-unstable-v6-client-protocol.h"
 
+struct wlr_wl_backend *get_wl_backend_from_backend(
+		struct wlr_backend *wlr_backend) {
+	assert(wlr_backend_is_wl(wlr_backend));
+	return (struct wlr_wl_backend *)wlr_backend;
+}
+
 static int dispatch_events(int fd, uint32_t mask, void *data) {
 	struct wlr_wl_backend *backend = data;
 	int count = 0;
@@ -39,8 +45,8 @@ static int dispatch_events(int fd, uint32_t mask, void *data) {
  * compositor and creates surfaces for each output, then registers globals on
  * the specified display.
  */
-static bool backend_start(struct wlr_backend *_backend) {
-	struct wlr_wl_backend *backend = (struct wlr_wl_backend *)_backend;
+static bool backend_start(struct wlr_backend *wlr_backend) {
+	struct wlr_wl_backend *backend = get_wl_backend_from_backend(wlr_backend);
 	wlr_log(WLR_INFO, "Initializating wayland backend");
 
 	poll_wl_registry(backend);
@@ -66,7 +72,7 @@ static bool backend_start(struct wlr_backend *_backend) {
 }
 
 static void backend_destroy(struct wlr_backend *wlr_backend) {
-	struct wlr_wl_backend *backend = (struct wlr_wl_backend *)wlr_backend;
+	struct wlr_wl_backend *backend = get_wl_backend_from_backend(wlr_backend);
 	if (backend == NULL) {
 		return;
 	}
@@ -118,7 +124,7 @@ static void backend_destroy(struct wlr_backend *wlr_backend) {
 
 static struct wlr_renderer *backend_get_renderer(
 		struct wlr_backend *wlr_backend) {
-	struct wlr_wl_backend *backend = (struct wlr_wl_backend *)wlr_backend;
+	struct wlr_wl_backend *backend = get_wl_backend_from_backend(wlr_backend);
 	return backend->renderer;
 }
 
diff --git a/backend/wayland/output.c b/backend/wayland/output.c
index 2fd35a3a..4eb99a3b 100644
--- a/backend/wayland/output.c
+++ b/backend/wayland/output.c
@@ -15,7 +15,11 @@
 #include "util/signal.h"
 #include "xdg-shell-unstable-v6-client-protocol.h"
 
-int os_create_anonymous_file(off_t size);
+static struct wlr_wl_output *get_wl_output_from_output(
+		struct wlr_output *wlr_output) {
+	assert(wlr_output_is_wl(wlr_output));
+	return (struct wlr_wl_output *)wlr_output;
+}
 
 static struct wl_callback_listener frame_listener;
 
@@ -33,9 +37,9 @@ static struct wl_callback_listener frame_listener = {
 	.done = surface_frame_callback
 };
 
-static bool output_set_custom_mode(struct wlr_output *_output,
+static bool output_set_custom_mode(struct wlr_output *wlr_output,
 		int32_t width, int32_t height, int32_t refresh) {
-	struct wlr_wl_output *output = (struct wlr_wl_output *)_output;
+	struct wlr_wl_output *output = get_wl_output_from_output(wlr_output);
 	wl_egl_window_resize(output->egl_window, width, height, 0, 0);
 	wlr_output_update_custom_mode(&output->wlr_output, width, height, 0);
 	return true;
@@ -44,7 +48,7 @@ static bool output_set_custom_mode(struct wlr_output *_output,
 static bool output_make_current(struct wlr_output *wlr_output,
 		int *buffer_age) {
 	struct wlr_wl_output *output =
-		(struct wlr_wl_output *)wlr_output;
+		get_wl_output_from_output(wlr_output);
 	return wlr_egl_make_current(&output->backend->egl, output->egl_surface,
 		buffer_age);
 }
@@ -52,7 +56,7 @@ static bool output_make_current(struct wlr_output *wlr_output,
 static bool output_swap_buffers(struct wlr_output *wlr_output,
 		pixman_region32_t *damage) {
 	struct wlr_wl_output *output =
-		(struct wlr_wl_output *)wlr_output;
+		get_wl_output_from_output(wlr_output);
 
 	if (output->frame_callback != NULL) {
 		wlr_log(WLR_ERROR, "Skipping buffer swap");
@@ -66,21 +70,22 @@ static bool output_swap_buffers(struct wlr_output *wlr_output,
 		damage);
 }
 
-static void output_transform(struct wlr_output *_output,
+static void output_transform(struct wlr_output *wlr_output,
 		enum wl_output_transform transform) {
-	struct wlr_wl_output *output = (struct wlr_wl_output *)_output;
+	struct wlr_wl_output *output = get_wl_output_from_output(wlr_output);
 	output->wlr_output.transform = transform;
 }
 
 static bool output_set_cursor(struct wlr_output *wlr_output,
 		struct wlr_texture *texture, int32_t scale,
-		enum wl_output_transform transform, int32_t hotspot_x, int32_t hotspot_y,
-		bool update_texture) {
-	struct wlr_wl_output *output = (struct wlr_wl_output *)wlr_output;
+		enum wl_output_transform transform,
+		int32_t hotspot_x, int32_t hotspot_y, bool update_texture) {
+	struct wlr_wl_output *output = get_wl_output_from_output(wlr_output);
 	struct wlr_wl_backend *backend = output->backend;
 
 	struct wlr_box hotspot = { .x = hotspot_x, .y = hotspot_y };
-	wlr_box_transform(&hotspot, wlr_output_transform_invert(wlr_output->transform),
+	wlr_box_transform(&hotspot,
+		wlr_output_transform_invert(wlr_output->transform),
 		output->cursor.width, output->cursor.height, &hotspot);
 
 	// TODO: use output->wlr_output.transform to transform pixels and hotpot
@@ -147,8 +152,7 @@ static bool output_set_cursor(struct wlr_output *wlr_output,
 }
 
 static void output_destroy(struct wlr_output *wlr_output) {
-	struct wlr_wl_output *output =
-		(struct wlr_wl_output *)wlr_output;
+	struct wlr_wl_output *output = get_wl_output_from_output(wlr_output);
 	if (output == NULL) {
 		return;
 	}
@@ -215,7 +219,8 @@ static struct zxdg_surface_v6_listener xdg_surface_listener = {
 	.configure = xdg_surface_handle_configure,
 };
 
-static void xdg_toplevel_handle_configure(void *data, struct zxdg_toplevel_v6 *xdg_toplevel,
+static void xdg_toplevel_handle_configure(void *data,
+		struct zxdg_toplevel_v6 *xdg_toplevel,
 		int32_t width, int32_t height, struct wl_array *states) {
 	struct wlr_wl_output *output = data;
 	assert(output && output->xdg_toplevel == xdg_toplevel);
@@ -228,7 +233,8 @@ static void xdg_toplevel_handle_configure(void *data, struct zxdg_toplevel_v6 *x
 	wlr_output_update_custom_mode(&output->wlr_output, width, height, 0);
 }
 
-static void xdg_toplevel_handle_close(void *data, struct zxdg_toplevel_v6 *xdg_toplevel) {
+static void xdg_toplevel_handle_close(void *data,
+		struct zxdg_toplevel_v6 *xdg_toplevel) {
 	struct wlr_wl_output *output = data;
 	assert(output && output->xdg_toplevel == xdg_toplevel);
 
@@ -240,9 +246,8 @@ static struct zxdg_toplevel_v6_listener xdg_toplevel_listener = {
 	.close = xdg_toplevel_handle_close,
 };
 
-struct wlr_output *wlr_wl_output_create(struct wlr_backend *_backend) {
-	assert(wlr_backend_is_wl(_backend));
-	struct wlr_wl_backend *backend = (struct wlr_wl_backend *)_backend;
+struct wlr_output *wlr_wl_output_create(struct wlr_backend *wlr_backend) {
+	struct wlr_wl_backend *backend = get_wl_backend_from_backend(wlr_backend);
 	if (!backend->started) {
 		++backend->requested_outputs;
 		return NULL;
diff --git a/backend/wayland/wl_seat.c b/backend/wayland/wl_seat.c
index 8fb4aa5f..562d9431 100644
--- a/backend/wayland/wl_seat.c
+++ b/backend/wayland/wl_seat.c
@@ -122,11 +122,11 @@ static void pointer_handle_axis(void *data, struct wl_pointer *wl_pointer,
 }
 
 static void pointer_handle_frame(void *data, struct wl_pointer *wl_pointer) {
-
+	// This space is intentionally left blank
 }
 
-static void pointer_handle_axis_source(void *data, struct wl_pointer *wl_pointer,
-		uint32_t axis_source) {
+static void pointer_handle_axis_source(void *data,
+		struct wl_pointer *wl_pointer, uint32_t axis_source) {
 	struct wlr_wl_backend *backend = data;
 	struct wlr_wl_pointer *pointer = backend->current_pointer;
 	if (pointer == NULL) {
@@ -138,11 +138,11 @@ static void pointer_handle_axis_source(void *data, struct wl_pointer *wl_pointer
 
 static void pointer_handle_axis_stop(void *data, struct wl_pointer *wl_pointer,
 		uint32_t time, uint32_t axis) {
-
+	// This space is intentionally left blank
 }
 
-static void pointer_handle_axis_discrete(void *data, struct wl_pointer *wl_pointer,
-		uint32_t axis, int32_t discrete) {
+static void pointer_handle_axis_discrete(void *data,
+		struct wl_pointer *wl_pointer, uint32_t axis, int32_t discrete) {
 	struct wlr_wl_backend *backend = data;
 	struct wlr_wl_pointer *pointer = backend->current_pointer;
 	if (pointer == NULL) {
@@ -239,9 +239,9 @@ static void keyboard_handle_modifiers(void *data, struct wl_keyboard *wl_keyboar
 		mods_locked, group);
 }
 
-static void keyboard_handle_repeat_info(void *data, struct wl_keyboard *wl_keyboard,
-	int32_t rate, int32_t delay) {
-
+static void keyboard_handle_repeat_info(void *data,
+		struct wl_keyboard *wl_keyboard, int32_t rate, int32_t delay) {
+	// This space is intentionally left blank
 }
 
 static struct wl_keyboard_listener keyboard_listener = {
@@ -253,8 +253,15 @@ static struct wl_keyboard_listener keyboard_listener = {
 	.repeat_info = keyboard_handle_repeat_info
 };
 
+static struct wlr_wl_input_device *get_wl_input_device_from_input_device(
+		struct wlr_input_device *wlr_dev) {
+	assert(wlr_input_device_is_wl(wlr_dev));
+	return (struct wlr_wl_input_device *)wlr_dev;
+}
+
 static void input_device_destroy(struct wlr_input_device *wlr_dev) {
-	struct wlr_wl_input_device *dev = (struct wlr_wl_input_device *)wlr_dev;
+	struct wlr_wl_input_device *dev =
+		get_wl_input_device_from_input_device(wlr_dev);
 	if (dev->resource) {
 		wl_proxy_destroy(dev->resource);
 	}
@@ -399,7 +406,8 @@ static void seat_handle_capabilities(void *data, struct wl_seat *wl_seat,
 	}
 }
 
-static void seat_handle_name(void *data, struct wl_seat *wl_seat, const char *name) {
+static void seat_handle_name(void *data, struct wl_seat *wl_seat,
+		const char *name) {
 	struct wlr_wl_backend *backend = data;
 	assert(backend->seat == wl_seat);
 	// Do we need to check if seatName was previously set for name change?
diff --git a/backend/x11/backend.c b/backend/x11/backend.c
index 0ff2925d..7053e2f0 100644
--- a/backend/x11/backend.c
+++ b/backend/x11/backend.c
@@ -1,4 +1,5 @@
 #define _POSIX_C_SOURCE 200112L
+#include <assert.h>
 #include <limits.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -22,8 +23,8 @@
 #include "backend/x11.h"
 #include "util/signal.h"
 
-struct wlr_x11_output *get_x11_output_from_window_id(struct wlr_x11_backend *x11,
-		xcb_window_t window) {
+struct wlr_x11_output *get_x11_output_from_window_id(
+		struct wlr_x11_backend *x11, xcb_window_t window) {
 	struct wlr_x11_output *output;
 	wl_list_for_each(output, &x11->outputs, link) {
 		if (output->win == window) {
@@ -88,8 +89,14 @@ static int x11_event(int fd, uint32_t mask, void *data) {
 	return 0;
 }
 
+struct wlr_x11_backend *get_x11_backend_from_backend(
+		struct wlr_backend *wlr_backend) {
+	assert(wlr_backend_is_x11(wlr_backend));
+	return (struct wlr_x11_backend *)wlr_backend;
+}
+
 static bool backend_start(struct wlr_backend *backend) {
-	struct wlr_x11_backend *x11 = (struct wlr_x11_backend *)backend;
+	struct wlr_x11_backend *x11 = get_x11_backend_from_backend(backend);
 	x11->started = true;
 
 	struct {
@@ -183,7 +190,7 @@ static void backend_destroy(struct wlr_backend *backend) {
 		return;
 	}
 
-	struct wlr_x11_backend *x11 = (struct wlr_x11_backend *)backend;
+	struct wlr_x11_backend *x11 = get_x11_backend_from_backend(backend);
 
 	struct wlr_x11_output *output, *tmp;
 	wl_list_for_each_safe(output, tmp, &x11->outputs, link) {
@@ -213,7 +220,7 @@ static void backend_destroy(struct wlr_backend *backend) {
 
 static struct wlr_renderer *backend_get_renderer(
 		struct wlr_backend *backend) {
-	struct wlr_x11_backend *x11 = (struct wlr_x11_backend *)backend;
+	struct wlr_x11_backend *x11 = get_x11_backend_from_backend(backend);
 	return x11->renderer;
 }
 
@@ -234,7 +241,8 @@ static void handle_display_destroy(struct wl_listener *listener, void *data) {
 }
 
 struct wlr_backend *wlr_x11_backend_create(struct wl_display *display,
-		const char *x11_display, wlr_renderer_create_func_t create_renderer_func) {
+		const char *x11_display,
+		wlr_renderer_create_func_t create_renderer_func) {
 	struct wlr_x11_backend *x11 = calloc(1, sizeof(*x11));
 	if (!x11) {
 		return NULL;
diff --git a/backend/x11/output.c b/backend/x11/output.c
index b678296d..e0210b1a 100644
--- a/backend/x11/output.c
+++ b/backend/x11/output.c
@@ -15,7 +15,8 @@ static int signal_frame(void *data) {
 	return 0;
 }
 
-static void parse_xcb_setup(struct wlr_output *output, xcb_connection_t *xcb_conn) {
+static void parse_xcb_setup(struct wlr_output *output,
+		xcb_connection_t *xcb_conn) {
 	const xcb_setup_t *xcb_setup = xcb_get_setup(xcb_conn);
 
 	snprintf(output->make, sizeof(output->make), "%.*s",
@@ -26,8 +27,14 @@ static void parse_xcb_setup(struct wlr_output *output, xcb_connection_t *xcb_con
 			xcb_setup->protocol_minor_version);
 }
 
+static struct wlr_x11_output *get_x11_output_from_output(
+		struct wlr_output *wlr_output) {
+	assert(wlr_output_is_x11(wlr_output));
+	return (struct wlr_x11_output *)wlr_output;
+}
+
 static void output_set_refresh(struct wlr_output *wlr_output, int32_t refresh) {
-	struct wlr_x11_output *output = (struct wlr_x11_output *)wlr_output;
+	struct wlr_x11_output *output = get_x11_output_from_output(wlr_output);
 
 	if (refresh <= 0) {
 		refresh = X11_DEFAULT_REFRESH;
@@ -41,18 +48,20 @@ static void output_set_refresh(struct wlr_output *wlr_output, int32_t refresh) {
 
 static bool output_set_custom_mode(struct wlr_output *wlr_output,
 		int32_t width, int32_t height, int32_t refresh) {
-	struct wlr_x11_output *output = (struct wlr_x11_output *)wlr_output;
+	struct wlr_x11_output *output = get_x11_output_from_output(wlr_output);
 	struct wlr_x11_backend *x11 = output->x11;
 
 	output_set_refresh(&output->wlr_output, refresh);
 
 	const uint32_t values[] = { width, height };
-	xcb_void_cookie_t cookie = xcb_configure_window_checked(x11->xcb_conn, output->win,
+	xcb_void_cookie_t cookie = xcb_configure_window_checked(
+		x11->xcb_conn, output->win,
 		XCB_CONFIG_WINDOW_WIDTH | XCB_CONFIG_WINDOW_HEIGHT, values);
 
 	xcb_generic_error_t *error;
 	if ((error = xcb_request_check(x11->xcb_conn, cookie))) {
-		wlr_log(WLR_ERROR, "Could not set window size to %dx%d\n", width, height);
+		wlr_log(WLR_ERROR, "Could not set window size to %dx%d\n",
+			width, height);
 		free(error);
 		return false;
 	}
@@ -62,12 +71,12 @@ static bool output_set_custom_mode(struct wlr_output *wlr_output,
 
 static void output_transform(struct wlr_output *wlr_output,
 		enum wl_output_transform transform) {
-	struct wlr_x11_output *output = (struct wlr_x11_output *)wlr_output;
+	struct wlr_x11_output *output = get_x11_output_from_output(wlr_output);
 	output->wlr_output.transform = transform;
 }
 
 static void output_destroy(struct wlr_output *wlr_output) {
-	struct wlr_x11_output *output = (struct wlr_x11_output *)wlr_output;
+	struct wlr_x11_output *output = get_x11_output_from_output(wlr_output);
 	struct wlr_x11_backend *x11 = output->x11;
 
 	wlr_input_device_destroy(&output->pointer_dev);
@@ -80,8 +89,9 @@ static void output_destroy(struct wlr_output *wlr_output) {
 	free(output);
 }
 
-static bool output_make_current(struct wlr_output *wlr_output, int *buffer_age) {
-	struct wlr_x11_output *output = (struct wlr_x11_output *)wlr_output;
+static bool output_make_current(struct wlr_output *wlr_output,
+		int *buffer_age) {
+	struct wlr_x11_output *output = get_x11_output_from_output(wlr_output);
 	struct wlr_x11_backend *x11 = output->x11;
 
 	return wlr_egl_make_current(&x11->egl, output->surf, buffer_age);
@@ -104,8 +114,7 @@ static const struct wlr_output_impl output_impl = {
 };
 
 struct wlr_output *wlr_x11_output_create(struct wlr_backend *backend) {
-	assert(wlr_backend_is_x11(backend));
-	struct wlr_x11_backend *x11 = (struct wlr_x11_backend *)backend;
+	struct wlr_x11_backend *x11 = get_x11_backend_from_backend(backend);
 
 	if (!x11->started) {
 		++x11->requested_outputs;
@@ -198,7 +207,8 @@ void handle_x11_configure_notify(struct wlr_x11_output *output,
 		// Move the pointer to its new location
 		update_x11_pointer_position(output, output->x11->time);
 	} else {
-		wlr_log(WLR_DEBUG,"Ignoring X11 configure event for height=%d, width=%d",
+		wlr_log(WLR_DEBUG,
+			"Ignoring X11 configure event for height=%d, width=%d",
 			ev->width, ev->height);
 	}
 }
diff --git a/include/backend/drm/drm.h b/include/backend/drm/drm.h
index 6fe031e2..ac23cd9a 100644
--- a/include/backend/drm/drm.h
+++ b/include/backend/drm/drm.h
@@ -138,6 +138,8 @@ struct wlr_drm_connector {
 	struct wl_list link;
 };
 
+struct wlr_drm_backend *get_drm_backend_from_backend(
+	struct wlr_backend *wlr_backend);
 bool check_drm_features(struct wlr_drm_backend *drm);
 bool init_drm_resources(struct wlr_drm_backend *drm);
 void finish_drm_resources(struct wlr_drm_backend *drm);
diff --git a/include/backend/headless.h b/include/backend/headless.h
index add4c4e8..35280862 100644
--- a/include/backend/headless.h
+++ b/include/backend/headless.h
@@ -34,4 +34,7 @@ struct wlr_headless_input_device {
 	struct wlr_headless_backend *backend;
 };
 
+struct wlr_headless_backend *headless_backend_from_backend(
+	struct wlr_backend *wlr_backend);
+
 #endif
diff --git a/include/backend/libinput.h b/include/backend/libinput.h
index d1fb3a44..9531091f 100644
--- a/include/backend/libinput.h
+++ b/include/backend/libinput.h
@@ -4,6 +4,7 @@
 #include <libinput.h>
 #include <wayland-server-core.h>
 #include <wlr/backend/interface.h>
+#include <wlr/backend/libinput.h>
 #include <wlr/interfaces/wlr_input_device.h>
 #include <wlr/types/wlr_input_device.h>
 #include <wlr/types/wlr_list.h>
diff --git a/include/backend/wayland.h b/include/backend/wayland.h
index 46f18c84..47585d9e 100644
--- a/include/backend/wayland.h
+++ b/include/backend/wayland.h
@@ -78,6 +78,8 @@ struct wlr_wl_pointer {
 	struct wl_listener output_destroy;
 };
 
+struct wlr_wl_backend *get_wl_backend_from_backend(
+	struct wlr_backend *wlr_backend);
 void poll_wl_registry(struct wlr_wl_backend *backend);
 void update_wl_output_cursor(struct wlr_wl_output *output);
 struct wlr_wl_pointer *pointer_get_wl(struct wlr_pointer *wlr_pointer);
diff --git a/include/backend/x11.h b/include/backend/x11.h
index f5557343..38aaad50 100644
--- a/include/backend/x11.h
+++ b/include/backend/x11.h
@@ -72,8 +72,10 @@ struct wlr_x11_backend {
 	struct wl_listener display_destroy;
 };
 
-struct wlr_x11_output *get_x11_output_from_window_id(struct wlr_x11_backend *x11,
-	xcb_window_t window);
+struct wlr_x11_backend *get_x11_backend_from_backend(
+	struct wlr_backend *wlr_backend);
+struct wlr_x11_output *get_x11_output_from_window_id(
+	struct wlr_x11_backend *x11, xcb_window_t window);
 
 extern const struct wlr_keyboard_impl keyboard_impl;
 extern const struct wlr_pointer_impl pointer_impl;