Merge pull request #978 from emersion/wlr-backend-env

backend: add WLR_BACKEND env variable

backend/backend.c

@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 200809L
 #include <assert.h>
 #include <errno.h>
 #include <libinput.h>
@@ -6,6 +7,7 @@
 #include <unistd.h>
 #include <wayland-server.h>
 #include <wlr/backend/drm.h>
+#include <wlr/backend/headless.h>
 #include <wlr/backend/interface.h>
 #include <wlr/backend/libinput.h>
 #include <wlr/backend/multi.h>
@@ -101,6 +103,76 @@ static struct wlr_backend *attempt_x11_backend(struct wl_display *display,
 }
 #endif
 
+static struct wlr_backend *attempt_headless_backend(
+		struct wl_display *display) {
+	struct wlr_backend *backend = wlr_headless_backend_create(display);
+	if (backend == NULL) {
+		return NULL;
+	}
+
+	size_t outputs = parse_outputs_env("WLR_HEADLESS_OUTPUTS");
+	for (size_t i = 0; i < outputs; ++i) {
+		wlr_headless_add_output(backend, 1280, 720);
+	}
+
+	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);
+#ifdef WLR_HAS_X11_BACKEND
+	} else if (strcmp(name, "x11") == 0) {
+		return attempt_x11_backend(display, NULL);
+#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;
+}
+
 struct wlr_backend *wlr_backend_autocreate(struct wl_display *display) {
 	struct wlr_backend *backend = wlr_multi_backend_create(display);
 	if (!backend) {
@@ -108,6 +180,42 @@ 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;
+		}
+
+		char *saveptr;
+		char *name = strtok_r(names, ",", &saveptr);
+		while (name != NULL) {
+			struct wlr_backend *subbackend =
+				attempt_backend_by_name(display, backend, &session, name);
+			if (subbackend == NULL) {
+				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;
+			}
+
+			name = strtok_r(NULL, ",", &saveptr);
+		}
+
+		return backend;
+	}
+
 	if (getenv("WAYLAND_DISPLAY") || getenv("_WAYLAND_DISPLAY") ||
 			getenv("WAYLAND_SOCKET")) {
 		struct wlr_backend *wl_backend = attempt_wl_backend(display);
@@ -130,7 +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);
@@ -138,40 +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;
 	}
 

backend/multi/backend.c

@@ -130,20 +130,29 @@ static struct subbackend_state *multi_backend_get_subbackend(struct wlr_multi_ba
 	return NULL;
 }
 
-void wlr_multi_backend_add(struct wlr_backend *_multi,
+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;
 
 	if (multi_backend_get_subbackend(multi, backend)) {
 		// already added
-		return;
+		return true;
 	}
 
-	struct subbackend_state *sub;
+	struct wlr_renderer *multi_renderer =
-	if (!(sub = calloc(1, sizeof(struct subbackend_state)))) {
+		multi_backend_get_renderer(&multi->backend);
+	struct wlr_renderer *backend_renderer = wlr_backend_get_renderer(backend);
+	if (multi_renderer != NULL && backend_renderer != NULL) {
+		wlr_log(L_ERROR, "Could not add backend: multiple renderers at the "
+			"same time aren't supported");
+		return false;
+	}
+
+	struct subbackend_state *sub = calloc(1, sizeof(struct subbackend_state));
+	if (sub == NULL) {
 		wlr_log(L_ERROR, "Could not add backend: allocation failed");
-		return;
+		return false;
 	}
 	wl_list_insert(&multi->backends, &sub->link);
 
@@ -160,6 +169,7 @@ void wlr_multi_backend_add(struct wlr_backend *_multi,
 	sub->new_output.notify = new_output_reemit;
 
 	wlr_signal_emit_safe(&multi->events.backend_add, backend);
+	return true;
 }
 
 void wlr_multi_backend_remove(struct wlr_backend *_multi,

backend/wayland/backend.c

@@ -87,7 +87,9 @@ static void backend_destroy(struct wlr_backend *wlr_backend) {
 
 	free(backend->seat_name);
 
-	wl_event_source_remove(backend->remote_display_src);
+	if (backend->remote_display_src) {
+		wl_event_source_remove(backend->remote_display_src);
+	}
 	wlr_renderer_destroy(backend->renderer);
 	wlr_egl_finish(&backend->egl);
 	if (backend->pointer) {

docs/env_vars.md

@@ -2,19 +2,26 @@ wlroots reads these environment variables
 
 wlroots specific
 ----------------
-* *WLR_DRM_DEVICES*: specifies the DRM devices (as a colon separated list) instead of auto probing them. The first existing device in this list is considered the primary DRM device.
+* *WLR_DRM_DEVICES*: specifies the DRM devices (as a colon separated list)
-* *WLR_DRM_NO_ATOMIC*: set to 1 to use legacy DRM interface instead of atomic mode setting
+  instead of auto probing them. The first existing device in this list is
+  considered the primary DRM device.
+* *WLR_DRM_NO_ATOMIC*: set to 1 to use legacy DRM interface instead of atomic
+  mode setting
 * *WLR_LIBINPUT_NO_DEVICES*: set to 1 to not fail without any input devices
+* *WLR_BACKENDS*: comma-separated list of backends to use (available backends:
+  wayland, x11, headless)
 * *WLR_WL_OUTPUTS*: when using the wayland backend specifies the number of outputs
 * *WLR_X11_OUTPUTS*: when using the X11 backend specifies the number of outputs
 
 rootston specific
 ------------------
-* *XKB_DEFAULT_RULES*, *XKB_DEFAULT_MODEL*, *XKB_DEFAULT_LAYOUT*, *XKB_DEFAULT_VARIANT*, *XKB_DEFAULT_OPTIONS*: xkb setup
+* *XKB_DEFAULT_RULES*, *XKB_DEFAULT_MODEL*, *XKB_DEFAULT_LAYOUT*,
+  *XKB_DEFAULT_VARIANT*, *XKB_DEFAULT_OPTIONS*: xkb setup
 
 generic
 -------
 * *DISPLAY*: if set probe X11 backend in *wlr_backend_autocreate*
-* *WAYLAND_DISPLAY*, *_WAYLAND_DISPLAY*, *WAYLAND_SOCKET*: if set probe Wayland backend in *wlr_backend_autocreate*
+* *WAYLAND_DISPLAY*, *_WAYLAND_DISPLAY*, *WAYLAND_SOCKET*: if set probe Wayland
+  backend in *wlr_backend_autocreate*
 * *XCURSOR_PATH*: directory where xcursors are located
 * *XDG_RUNTIME_DIR*: used to store non persistent temporary files

include/wlr/backend/multi.h

@@ -13,7 +13,7 @@ struct wlr_backend *wlr_multi_backend_create(struct wl_display *display);
  * Adds the given backend to the multi backend. This should be done before the
  * new backend is started.
  */
-void wlr_multi_backend_add(struct wlr_backend *multi,
+bool wlr_multi_backend_add(struct wlr_backend *multi,
 	struct wlr_backend *backend);
 
 void wlr_multi_backend_remove(struct wlr_backend *multi,