backend/session: introduce wlr_device_change_event

This struct contains additional information for session device
change events, such as the DRM connector ID that has changed.

backend/session/session.c

@@ -139,6 +139,27 @@ static bool is_drm_card(const char *sysname) {
 	return true;
 }
 
+static void read_udev_change_event(struct wlr_device_change_event *event,
+		struct udev_device *udev_dev) {
+	const char *hotplug = udev_device_get_property_value(udev_dev, "HOTPLUG");
+	if (hotplug != NULL && strcmp(hotplug, "1") == 0) {
+		event->type = WLR_DEVICE_HOTPLUG;
+		struct wlr_device_hotplug_event *hotplug = &event->hotplug;
+
+		const char *connector =
+			udev_device_get_property_value(udev_dev, "CONNECTOR");
+		if (connector != NULL) {
+			hotplug->connector_id = strtoul(connector, NULL, 10);
+		}
+
+		const char *prop =
+			udev_device_get_property_value(udev_dev, "PROPERTY");
+		if (prop != NULL) {
+			hotplug->prop_id = strtoul(prop, NULL, 10);
+		}
+	}
+}
+
 static int handle_udev_event(int fd, uint32_t mask, void *data) {
 	struct wlr_session *session = data;
 
@@ -180,7 +201,9 @@ static int handle_udev_event(int fd, uint32_t mask, void *data) {
 
 			if (strcmp(action, "change") == 0) {
 				wlr_log(WLR_DEBUG, "DRM device %s changed", sysname);
-				wlr_signal_emit_safe(&dev->events.change, NULL);
+				struct wlr_device_change_event event = {0};
+				read_udev_change_event(&event, udev_dev);
+				wlr_signal_emit_safe(&dev->events.change, &event);
 			} else if (strcmp(action, "remove") == 0) {
 				wlr_log(WLR_DEBUG, "DRM device %s removed", sysname);
 				wlr_signal_emit_safe(&dev->events.remove, NULL);

include/wlr/backend/session.h

@@ -15,7 +15,7 @@ struct wlr_device {
 	struct wl_list link;
 
 	struct {
-		struct wl_signal change;
+		struct wl_signal change; // struct wlr_device_change_event
 		struct wl_signal remove;
 	} events;
 };
@@ -57,6 +57,22 @@ struct wlr_session_add_event {
 	const char *path;
 };
 
+enum wlr_device_change_type {
+	WLR_DEVICE_HOTPLUG = 1,
+};
+
+struct wlr_device_hotplug_event {
+	uint32_t connector_id;
+	uint32_t prop_id;
+};
+
+struct wlr_device_change_event {
+	enum wlr_device_change_type type;
+	union {
+		struct wlr_device_hotplug_event hotplug;
+	};
+};
+
 /*
  * Opens a session, taking control of the current virtual terminal.
  * This should not be called if another program is already in control