backend: support creating DRM and libinput via WLR_BACKENDS

backend/backend.c

@@ -118,7 +118,33 @@ static struct wlr_backend *attempt_headless_backend(
 	return backend;
 }
 
+static struct wlr_backend *attempt_drm_backend(struct wl_display *display,
+		struct wlr_backend *backend, struct wlr_session *session) {
+	int gpus[8];
+	size_t num_gpus = wlr_session_find_gpus(session, 8, gpus);
+	struct wlr_backend *primary_drm = NULL;
+	wlr_log(L_INFO, "Found %zu GPUs", num_gpus);
+
+	for (size_t i = 0; i < num_gpus; ++i) {
+		struct wlr_backend *drm = wlr_drm_backend_create(display, session,
+			gpus[i], primary_drm);
+		if (!drm) {
+			wlr_log(L_ERROR, "Failed to open DRM device %d", gpus[i]);
+			continue;
+		}
+
+		if (!primary_drm) {
+			primary_drm = drm;
+		}
+
+		wlr_multi_backend_add(backend, drm);
+	}
+
+	return primary_drm;
+}
+
 static struct wlr_backend *attempt_backend_by_name(struct wl_display *display,
+		struct wlr_backend *backend, struct wlr_session **session,
 		const char *name) {
 	if (strcmp(name, "wayland") == 0) {
 		return attempt_wl_backend(display);
@@ -128,7 +154,22 @@ static struct wlr_backend *attempt_backend_by_name(struct wl_display *display,
 #endif
 	} else if (strcmp(name, "headless") == 0) {
 		return attempt_headless_backend(display);
+	} else if (strcmp(name, "drm") == 0 || strcmp(name, "libinput") == 0) {
+		// DRM and libinput need a session
+		*session = wlr_session_create(display);
+		if (!*session) {
+			wlr_log(L_ERROR, "failed to start a session");
+			return NULL;
 		}
+
+		if (strcmp(name, "libinput") == 0) {
+			return wlr_libinput_backend_create(display, *session);
+		} else {
+			return attempt_drm_backend(display, backend, *session);
+		}
+	}
+
+	wlr_log(L_ERROR, "unrecognized backend '%s'", name);
 	return NULL;
 }
 
@@ -139,11 +180,14 @@ struct wlr_backend *wlr_backend_autocreate(struct wl_display *display) {
 		return NULL;
 	}
 
+	struct wlr_session *session = NULL;
+
 	char *names = getenv("WLR_BACKENDS");
 	if (names) {
 		names = strdup(names);
 		if (names == NULL) {
 			wlr_log(L_ERROR, "allocation failed");
+			wlr_backend_destroy(backend);
 			return NULL;
 		}
 
@@ -151,13 +195,18 @@ struct wlr_backend *wlr_backend_autocreate(struct wl_display *display) {
 		char *name = strtok_r(names, ",", &saveptr);
 		while (name != NULL) {
 			struct wlr_backend *subbackend =
-				attempt_backend_by_name(display, name);
+				attempt_backend_by_name(display, backend, &session, name);
 			if (subbackend == NULL) {
-				wlr_log(L_ERROR, "unrecognized backend '%s'", name);
+				wlr_log(L_ERROR, "failed to start backend '%s'", name);
+				wlr_backend_destroy(backend);
+				wlr_session_destroy(session);
 				return NULL;
 			}
 
 			if (!wlr_multi_backend_add(backend, subbackend)) {
+				wlr_log(L_ERROR, "failed to add backend '%s'", name);
+				wlr_backend_destroy(backend);
+				wlr_session_destroy(session);
 				return NULL;
 			}
 
@@ -189,7 +238,7 @@ struct wlr_backend *wlr_backend_autocreate(struct wl_display *display) {
 #endif
 
 	// Attempt DRM+libinput
-	struct wlr_session *session = wlr_session_create(display);
+	session = wlr_session_create(display);
 	if (!session) {
 		wlr_log(L_ERROR, "Failed to start a DRM session");
 		wlr_backend_destroy(backend);
@@ -197,40 +246,21 @@ struct wlr_backend *wlr_backend_autocreate(struct wl_display *display) {
 	}
 
 	struct wlr_backend *libinput = wlr_libinput_backend_create(display, session);
-	if (libinput) {
+	if (!libinput) {
-		wlr_multi_backend_add(backend, libinput);
-	} else {
 		wlr_log(L_ERROR, "Failed to start libinput backend");
 		wlr_backend_destroy(backend);
 		wlr_session_destroy(session);
 		return NULL;
 	}
+	wlr_multi_backend_add(backend, libinput);
 
-	int gpus[8];
+	struct wlr_backend *primary_drm =
-	size_t num_gpus = wlr_session_find_gpus(session, 8, gpus);
+		attempt_drm_backend(display, backend, session);
-	struct wlr_backend *primary_drm = NULL;
-	wlr_log(L_INFO, "Found %zu GPUs", num_gpus);
-
-	for (size_t i = 0; i < num_gpus; ++i) {
-		struct wlr_backend *drm = wlr_drm_backend_create(display, session,
-			gpus[i], primary_drm);
-		if (!drm) {
-			wlr_log(L_ERROR, "Failed to open DRM device");
-			continue;
-		}
-
-		if (!primary_drm) {
-			primary_drm = drm;
-		}
-
-		wlr_multi_backend_add(backend, drm);
-	}
-
 	if (!primary_drm) {
 		wlr_log(L_ERROR, "Failed to open any DRM device");
 		wlr_backend_destroy(libinput);
-		wlr_session_destroy(session);
 		wlr_backend_destroy(backend);
+		wlr_session_destroy(session);
 		return NULL;
 	}