Rework session handling

Sessions can now be retrieved from a backend in a more general manner.
Multi-backend gets back its `session` field that contains the session
if one was created, removing the interfacing from multi backend with the
drm backend directly. This adds the possibility to use sessions even
without the drm backend.

It additionally fixes the bug that 2 session objects got created when
WLR_BACKENDS were set to "libinput,drm".

To allow vt switching without drm backend (and drm fd) on logind, start
listening to PropertiesChanged signals from dbus and parse the session
"Active" property when no master fd was created (this does not change
current drm backend behaviour in any way).

backend/backend.c

@@ -15,6 +15,7 @@
 #include <wlr/backend/wayland.h>
 #include <wlr/config.h>
 #include <wlr/util/log.h>
+#include "backend/multi.h"
 
 /* WLR_HAS_X11_BACKEND needs to be after wlr/config.h */
 #ifdef WLR_HAS_X11_BACKEND
@@ -56,6 +57,13 @@ struct wlr_renderer *wlr_backend_get_renderer(struct wlr_backend *backend) {
 	return NULL;
 }
 
+struct wlr_session *wlr_backend_get_session(struct wlr_backend *backend) {
+	if (backend->impl->get_session) {
+		return backend->impl->get_session(backend);
+	}
+	return NULL;
+}
+
 static size_t parse_outputs_env(const char *name) {
 	const char *outputs_str = getenv(name);
 	if (outputs_str == NULL) {
@@ -158,10 +166,12 @@ static struct wlr_backend *attempt_backend_by_name(struct wl_display *display,
 		return attempt_headless_backend(display, create_renderer_func);
 	} 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(WLR_ERROR, "failed to start a session");
-			return NULL;
+			*session = wlr_session_create(display);
+			if (!*session) {
+				wlr_log(WLR_ERROR, "failed to start a session");
+				return NULL;
+			}
 		}
 
 		if (strcmp(name, "libinput") == 0) {
@@ -178,13 +188,12 @@ static struct wlr_backend *attempt_backend_by_name(struct wl_display *display,
 struct wlr_backend *wlr_backend_autocreate(struct wl_display *display,
 		wlr_renderer_create_func_t create_renderer_func) {
 	struct wlr_backend *backend = wlr_multi_backend_create(display);
+	struct wlr_multi_backend *multi = (struct wlr_multi_backend *)backend;
 	if (!backend) {
 		wlr_log(WLR_ERROR, "could not allocate multibackend");
 		return NULL;
 	}
 
-	struct wlr_session *session = NULL;
-
 	char *names = getenv("WLR_BACKENDS");
 	if (names) {
 		names = strdup(names);
@@ -197,12 +206,12 @@ struct wlr_backend *wlr_backend_autocreate(struct wl_display *display,
 		char *saveptr;
 		char *name = strtok_r(names, ",", &saveptr);
 		while (name != NULL) {
-			struct wlr_backend *subbackend =
-				attempt_backend_by_name(display, backend, &session, name, create_renderer_func);
+			struct wlr_backend *subbackend = attempt_backend_by_name(display,
+				backend, &multi->session, name, create_renderer_func);
 			if (subbackend == NULL) {
 				wlr_log(WLR_ERROR, "failed to start backend '%s'", name);
 				wlr_backend_destroy(backend);
-				wlr_session_destroy(session);
+				wlr_session_destroy(multi->session);
 				free(names);
 				return NULL;
 			}
@@ -210,7 +219,7 @@ struct wlr_backend *wlr_backend_autocreate(struct wl_display *display,
 			if (!wlr_multi_backend_add(backend, subbackend)) {
 				wlr_log(WLR_ERROR, "failed to add backend '%s'", name);
 				wlr_backend_destroy(backend);
-				wlr_session_destroy(session);
+				wlr_session_destroy(multi->session);
 				free(names);
 				return NULL;
 			}
@@ -245,29 +254,30 @@ struct wlr_backend *wlr_backend_autocreate(struct wl_display *display,
 #endif
 
 	// Attempt DRM+libinput
-	session = wlr_session_create(display);
-	if (!session) {
+	multi->session = wlr_session_create(display);
+	if (!multi->session) {
 		wlr_log(WLR_ERROR, "Failed to start a DRM session");
 		wlr_backend_destroy(backend);
 		return NULL;
 	}
 
-	struct wlr_backend *libinput = wlr_libinput_backend_create(display, session);
+	struct wlr_backend *libinput = wlr_libinput_backend_create(display,
+		multi->session);
 	if (!libinput) {
 		wlr_log(WLR_ERROR, "Failed to start libinput backend");
 		wlr_backend_destroy(backend);
-		wlr_session_destroy(session);
+		wlr_session_destroy(multi->session);
 		return NULL;
 	}
 	wlr_multi_backend_add(backend, libinput);
 
-	struct wlr_backend *primary_drm =
-		attempt_drm_backend(display, backend, session, create_renderer_func);
+	struct wlr_backend *primary_drm = attempt_drm_backend(display, backend,
+		multi->session, create_renderer_func);
 	if (!primary_drm) {
 		wlr_log(WLR_ERROR, "Failed to open any DRM device");
 		wlr_backend_destroy(libinput);
 		wlr_backend_destroy(backend);
-		wlr_session_destroy(session);
+		wlr_session_destroy(multi->session);
 		return NULL;
 	}
 

backend/drm/backend.c

@@ -193,8 +193,3 @@ error_fd:
 	free(drm);
 	return NULL;
 }
-
-struct wlr_session *wlr_drm_backend_get_session(struct wlr_backend *backend) {
-	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
-	return drm->session;
-}

backend/multi/backend.c

@@ -1,7 +1,6 @@
 #include <assert.h>
 #include <stdbool.h>
 #include <stdlib.h>
-#include <wlr/backend/drm.h>
 #include <wlr/backend/interface.h>
 #include <wlr/backend/session.h>
 #include <wlr/util/log.h>
@@ -72,10 +71,17 @@ static struct wlr_renderer *multi_backend_get_renderer(
 	return NULL;
 }
 
+static struct wlr_session *multi_backend_get_session(
+		struct wlr_backend *_backend) {
+	struct wlr_multi_backend *backend = multi_backend_from_backend(_backend);
+	return backend->session;
+}
+
 struct wlr_backend_impl backend_impl = {
 	.start = multi_backend_start,
 	.destroy = multi_backend_destroy,
 	.get_renderer = multi_backend_get_renderer,
+	.get_session = multi_backend_get_session,
 };
 
 static void handle_display_destroy(struct wl_listener *listener, void *data) {
@@ -191,17 +197,6 @@ void wlr_multi_backend_remove(struct wlr_backend *_multi,
 	}
 }
 
-struct wlr_session *wlr_multi_get_session(struct wlr_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)) {
-			return wlr_drm_backend_get_session(sub->backend);
-		}
-	}
-	return NULL;
-}
-
 bool wlr_multi_is_empty(struct wlr_backend *_backend) {
 	assert(wlr_backend_is_multi(_backend));
 	struct wlr_multi_backend *backend = (struct wlr_multi_backend *)_backend;

backend/session/logind.c

@@ -35,6 +35,11 @@ struct logind_session {
 
 	char *id;
 	char *path;
+
+	// specifies whether a drm device was taken
+	// if so, the session will be (de)activated with the drm fd,
+	// otherwise with the dbus PropertiesChanged on "active" signal
+	bool has_drm;
 };
 
 static struct logind_session *logind_session_from_session(
@@ -43,6 +48,30 @@ static struct logind_session *logind_session_from_session(
 	return (struct logind_session *)base;
 }
 
+static void parse_active(struct logind_session *session,
+		struct sd_bus_message *msg) {
+	int ret;
+	ret = sd_bus_message_enter_container(msg, 'v', "b");
+	if (ret < 0) {
+		wlr_log(WLR_ERROR, "Failed to parse D-Bus active property (1): %s",
+			strerror(-ret));
+		return;
+	}
+
+	bool active;
+	ret = sd_bus_message_read_basic(msg, 'b', &active);
+	if (ret < 0) {
+		wlr_log(WLR_ERROR, "Failed to parse D-Bus active property (2): %s",
+			strerror(-ret));
+		return;
+	}
+
+	if (!session->has_drm) {
+		session->base.active = active;
+		wlr_signal_emit_safe(&session->base.session_signal, session);
+	}
+}
+
 static int logind_take_device(struct wlr_session *base, const char *path) {
 	struct logind_session *session = logind_session_from_session(base);
 
@@ -57,6 +86,10 @@ static int logind_take_device(struct wlr_session *base, const char *path) {
 		return -1;
 	}
 
+	if (major(st.st_rdev) == DRM_MAJOR) {
+		session->has_drm = true;
+	}
+
 	ret = sd_bus_call_method(session->bus, "org.freedesktop.login1",
 		session->path, "org.freedesktop.login1.Session", "TakeDevice",
 		&error, &msg, "uu", major(st.st_rdev), minor(st.st_rdev));
@@ -262,6 +295,7 @@ static int pause_device(sd_bus_message *msg, void *userdata, sd_bus_error *ret_e
 	}
 
 	if (major == DRM_MAJOR) {
+		assert(session->has_drm);
 		session->base.active = false;
 		wlr_signal_emit_safe(&session->base.session_signal, session);
 	}
@@ -307,6 +341,107 @@ error:
 	return 0;
 }
 
+static int properties_changed(sd_bus_message *msg, void *userdata,
+		sd_bus_error *ret_error) {
+	struct logind_session *session = userdata;
+	int ret = 0;
+
+	// if we have drm fd we don't depend on this
+	if (session->has_drm) {
+		return 0;
+	}
+
+	// PropertiesChanged 1: interface
+	const char *interface;
+	ret = sd_bus_message_read_basic(msg, 's', &interface); // skip path
+	if (ret < 0) {
+		wlr_log(WLR_ERROR, "Failed to parse D-Bus PropertiesChanged (1) %s",
+			strerror(-ret));
+		goto error;
+	}
+
+	if (strcmp(interface, "org.freedesktop.login1.Session") != 0) {
+		// not interesting for us; ignore
+		wlr_log(WLR_DEBUG, "ignoring PropertiesChanged from %s", interface);
+		return 0;
+	}
+
+	// PropertiesChanged 2: changed properties with values
+	ret = sd_bus_message_enter_container(msg, 'a', "{sv}");
+	if (ret < 0) {
+		wlr_log(WLR_ERROR, "Failed to parse D-Bus PropertiesChanged (2) %s",
+			strerror(-ret));
+		goto error;
+	}
+
+	const char *s;
+	while ((ret = sd_bus_message_enter_container(msg, 'e', "sv")) > 0) {
+		ret = sd_bus_message_read_basic(msg, 's', &s);
+		if (ret < 0) {
+			wlr_log(WLR_ERROR, "Failed to parse D-Bus PropertiesChanged (3) %s",
+				strerror(-ret));
+			goto error;
+		}
+
+		if (strcmp(s, "Active") == 0) {
+			parse_active(session, msg);
+			return 0;
+		} else {
+			sd_bus_message_skip(msg, "{sv}");
+		}
+
+		ret = sd_bus_message_exit_container(msg);
+		if (ret < 0) {
+			wlr_log(WLR_ERROR, "Failed to parse D-Bus PropertiesChanged (4) %s",
+				strerror(-ret));
+			goto error;
+		}
+	}
+
+	if (ret < 0) {
+		wlr_log(WLR_ERROR, "Failed to parse D-Bus PropertiesChanged (5) %s",
+			strerror(-ret));
+		goto error;
+	}
+
+	ret = sd_bus_message_exit_container(msg);
+	if (ret < 0) {
+		wlr_log(WLR_ERROR, "Failed to parse D-Bus PropertiesChanged (6) %s",
+			strerror(-ret));
+		goto error;
+	}
+
+	// PropertiesChanged 3: changed properties without values
+	sd_bus_message_enter_container(msg, 'a', "s");
+	while ((ret = sd_bus_message_read_basic(msg, 's', &s)) > 0) {
+		if (strcmp(s, "Active") == 0) {
+			sd_bus_error error = SD_BUS_ERROR_NULL;
+			sd_bus_message *answer = NULL;
+			ret = sd_bus_call_method(session->bus, "org.freedesktop.login1",
+				session->path, "org.freedesktop.DBus.Properties", "Get",
+				&error, &answer, "ss", "org.freedesktop.login1.Session",
+				"Active");
+			if (ret < 0) {
+				wlr_log(WLR_ERROR, "Failed to get active property: '%s' (%s)",
+					error.message, strerror(ret));
+				goto error;
+			}
+
+			parse_active(session, answer);
+			return 0;
+		}
+	}
+
+	if (ret < 0) {
+		wlr_log(WLR_ERROR, "Failed to parse D-Bus PropertiesChanged (7) %s",
+			strerror(-ret));
+		goto error;
+	}
+
+error:
+	return 0;
+}
+
 static bool add_signal_matches(struct logind_session *session) {
 	int ret;
 
@@ -338,6 +473,14 @@ static bool add_signal_matches(struct logind_session *session) {
 		return false;
 	}
 
+	ret = sd_bus_match_signal(session->bus, NULL, "org.freedesktop.login1",
+		session->path, "org.freedesktop.DBus.Properties", "PropertiesChanged",
+		properties_changed, session);
+	if (ret < 0) {
+		wlr_log(WLR_ERROR, "Failed to add D-Bus match: %s", strerror(-ret));
+		return false;
+	}
+
 	return true;
 }
 

include/backend/multi.h

@@ -8,6 +8,7 @@
 
 struct wlr_multi_backend {
 	struct wlr_backend backend;
+	struct wlr_session *session;
 
 	struct wl_list backends;
 

include/wlr/backend.h

@@ -57,5 +57,10 @@ void wlr_backend_destroy(struct wlr_backend *backend);
  * Obtains the wlr_renderer reference this backend is using.
  */
 struct wlr_renderer *wlr_backend_get_renderer(struct wlr_backend *backend);
+/**
+ * Obtains the wlr_session reference from this backend if there is any.
+ * Might return NULL for backends that don't use a session.
+ */
+struct wlr_session *wlr_backend_get_session(struct wlr_backend *backend);
 
 #endif

include/wlr/backend/drm.h

@@ -34,6 +34,4 @@ bool wlr_output_is_drm(struct wlr_output *output);
 typedef struct _drmModeModeInfo drmModeModeInfo;
 bool wlr_drm_connector_add_mode(struct wlr_output *output, const drmModeModeInfo *mode);
 
-struct wlr_session *wlr_drm_backend_get_session(struct wlr_backend *backend);
-
 #endif

include/wlr/backend/interface.h

@@ -17,6 +17,7 @@ struct wlr_backend_impl {
 	bool (*start)(struct wlr_backend *backend);
 	void (*destroy)(struct wlr_backend *backend);
 	struct wlr_renderer *(*get_renderer)(struct wlr_backend *backend);
+	struct wlr_session *(*get_session)(struct wlr_backend *backend);
 };
 
 /**

rootston/keyboard.c

@@ -5,7 +5,6 @@
 #include <sys/wait.h>
 #include <unistd.h>
 #include <wayland-server.h>
-#include <wlr/backend/multi.h>
 #include <wlr/backend/session.h>
 #include <wlr/types/wlr_input_device.h>
 #include <wlr/types/wlr_pointer.h>
@@ -193,14 +192,13 @@ static bool keyboard_execute_compositor_binding(struct roots_keyboard *keyboard,
 	if (keysym >= XKB_KEY_XF86Switch_VT_1 &&
 			keysym <= XKB_KEY_XF86Switch_VT_12) {
 		struct roots_server *server = keyboard->input->server;
-		if (wlr_backend_is_multi(server->backend)) {
-			struct wlr_session *session =
-				wlr_multi_get_session(server->backend);
-			if (session) {
-				unsigned vt = keysym - XKB_KEY_XF86Switch_VT_1 + 1;
-				wlr_session_change_vt(session, vt);
-			}
+
+		struct wlr_session *session = wlr_backend_get_session(server->backend);
+		if (session) {
+			unsigned vt = keysym - XKB_KEY_XF86Switch_VT_1 + 1;
+			wlr_session_change_vt(session, vt);
 		}
+
 		return true;
 	}