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).

1 files changed, 143 insertions, 0 deletions

diff --git a/backend/session/logind.c b/backend/session/logind.c
index 39143a2f..b86cf3dc 100644
--- a/backend/session/logind.c
+++ b/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;
 }