backend/session: Remove session_impl

libseat provides all session functionality, so there is no longer need
for a session backend abstraction. The libseat device ID, seat handle
and event loop handle are moved to the main wlr_session and wlr_device
structs.

backend/session/session.c

@@ -1,8 +1,10 @@
 #define _POSIX_C_SOURCE 200809L
 #include <assert.h>
 #include <libudev.h>
+#include <stdarg.h>
 #include <stddef.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -10,7 +12,6 @@
 #include <time.h>
 #include <wayland-server-core.h>
 #include <wlr/backend/session.h>
-#include <wlr/backend/session/interface.h>
 #include <wlr/config.h>
 #include <wlr/util/log.h>
 #include <xf86drm.h>
@@ -18,15 +19,113 @@
 #include "backend/session/session.h"
 #include "util/signal.h"
 
+#include <libseat.h>
+
 #define WAIT_GPU_TIMEOUT 10000 // ms
 
-extern const struct session_impl session_libseat;
+static void handle_enable_seat(struct libseat *seat, void *data) {
+	struct wlr_session *session = data;
+	session->active = true;
+	wlr_signal_emit_safe(&session->events.active, NULL);
+}
 
-static const struct session_impl *const impls[] = {
-	&session_libseat,
-	NULL,
+static void handle_disable_seat(struct libseat *seat, void *data) {
+	struct wlr_session *session = data;
+	session->active = false;
+	wlr_signal_emit_safe(&session->events.active, NULL);
+	libseat_disable_seat(session->seat_handle);
+}
+
+static int libseat_event(int fd, uint32_t mask, void *data) {
+	struct wlr_session *session = data;
+	if (libseat_dispatch(session->seat_handle, 0) == -1) {
+		wlr_log_errno(WLR_ERROR, "Failed to dispatch libseat");
+		wl_display_terminate(session->display);
+	}
+	return 1;
+}
+
+static struct libseat_seat_listener seat_listener = {
+	.enable_seat = handle_enable_seat,
+	.disable_seat = handle_disable_seat,
 };
 
+static enum wlr_log_importance libseat_log_level_to_wlr(
+		enum libseat_log_level level) {
+	switch (level) {
+	case LIBSEAT_LOG_LEVEL_ERROR:
+		return WLR_ERROR;
+	case LIBSEAT_LOG_LEVEL_INFO:
+		return WLR_INFO;
+	default:
+		return WLR_DEBUG;
+	}
+}
+
+static void log_libseat(enum libseat_log_level level,
+		const char *fmt, va_list args) {
+	enum wlr_log_importance importance = libseat_log_level_to_wlr(level);
+
+	static char wlr_fmt[1024];
+	snprintf(wlr_fmt, sizeof(wlr_fmt), "[libseat] %s", fmt);
+
+	_wlr_vlog(importance, wlr_fmt, args);
+}
+
+static int libseat_session_init(struct wlr_session *session, struct wl_display *disp) {
+	libseat_set_log_handler(log_libseat);
+	libseat_set_log_level(LIBSEAT_LOG_LEVEL_INFO);
+
+	// libseat will take care of updating the logind state if necessary
+	setenv("XDG_SESSION_TYPE", "wayland", 1);
+
+	session->seat_handle = libseat_open_seat(&seat_listener, session);
+	if (session->seat_handle == NULL) {
+		wlr_log_errno(WLR_ERROR, "Unable to create seat");
+		return -1;
+	}
+
+	const char *seat_name = libseat_seat_name(session->seat_handle);
+	if (seat_name == NULL) {
+		wlr_log_errno(WLR_ERROR, "Unable to get seat info");
+		goto error;
+	}
+	snprintf(session->seat, sizeof(session->seat), "%s", seat_name);
+
+	struct wl_event_loop *event_loop = wl_display_get_event_loop(disp);
+	session->libseat_event = wl_event_loop_add_fd(event_loop, libseat_get_fd(session->seat_handle),
+		WL_EVENT_READABLE, libseat_event, session);
+	if (session->libseat_event == NULL) {
+		wlr_log(WLR_ERROR, "Failed to create libseat event source");
+		goto error;
+	}
+
+	// We may have received enable_seat immediately after the open_seat result,
+	// so, dispatch once without timeout to speed up activation.
+	if (libseat_dispatch(session->seat_handle, 0) == -1) {
+		wlr_log_errno(WLR_ERROR, "libseat dispatch failed");
+		goto error_dispatch;
+	}
+
+	wlr_log(WLR_INFO, "Successfully loaded libseat session");
+	return 0;
+
+error_dispatch:
+	wl_event_source_remove(session->libseat_event);
+	session->libseat_event = NULL;
+error:
+	libseat_close_seat(session->seat_handle);
+	session->seat_handle = NULL;
+	return -1;
+}
+
+static void libseat_session_finish(struct wlr_session *session) {
+	libseat_close_seat(session->seat_handle);
+	wl_event_source_remove(session->libseat_event);
+	session->seat_handle = NULL;
+	session->libseat_event = NULL;
+}
+
 static bool is_drm_card(const char *sysname) {
 	const char prefix[] = "card";
 	if (strncmp(sysname, prefix, strlen(prefix)) != 0) {
@@ -94,34 +193,21 @@ static void handle_display_destroy(struct wl_listener *listener, void *data) {
 	wlr_session_destroy(session);
 }
 
-void session_init(struct wlr_session *session) {
+struct wlr_session *wlr_session_create(struct wl_display *disp) {
+	struct wlr_session *session = calloc(1, sizeof(*session));
+	if (!session) {
+		wlr_log_errno(WLR_ERROR, "Allocation failed");
+		return NULL;
+	}
+
 	wl_signal_init(&session->events.active);
 	wl_signal_init(&session->events.add_drm_card);
 	wl_signal_init(&session->events.destroy);
 	wl_list_init(&session->devices);
-}
 
-struct wlr_session *wlr_session_create(struct wl_display *disp) {
-	struct wlr_session *session = NULL;
-
-	const char *env_wlr_session = getenv("WLR_SESSION");
-	if (env_wlr_session) {
-		if (strcmp(env_wlr_session, "libseat") == 0) {
-			session = session_libseat.create(disp);
-		} else {
-			wlr_log(WLR_ERROR, "Unsupported WLR_SESSION: %s",
-				env_wlr_session);
-		}
-	} else {
-		const struct session_impl *const *iter;
-		for (iter = impls; !session && *iter; ++iter) {
-			session = (*iter)->create(disp);
-		}
-	}
-
-	if (!session) {
+	if (libseat_session_init(session, disp) == -1) {
 		wlr_log(WLR_ERROR, "Failed to load session backend");
-		return NULL;
+		goto error_open;
 	}
 
 	session->udev = udev_new();
@@ -161,7 +247,9 @@ error_mon:
 error_udev:
 	udev_unref(session->udev);
 error_session:
-	session->impl->destroy(session);
+	libseat_session_finish(session);
+error_open:
+	free(session);
 	return NULL;
 }
 
@@ -177,13 +265,16 @@ void wlr_session_destroy(struct wlr_session *session) {
 	udev_monitor_unref(session->mon);
 	udev_unref(session->udev);
 
-	session->impl->destroy(session);
+	libseat_session_finish(session);
+	free(session);
 }
 
 struct wlr_device *wlr_session_open_file(struct wlr_session *session,
 		const char *path) {
-	int fd = session->impl->open(session, path);
-	if (fd < 0) {
+	int fd;
+	int device_id = libseat_open_device(session->seat_handle, path, &fd);
+	if (device_id == -1) {
+		wlr_log_errno(WLR_ERROR, "Failed to open device: '%s'", path);
 		return NULL;
 	}
 
@@ -201,12 +292,14 @@ struct wlr_device *wlr_session_open_file(struct wlr_session *session,
 
 	dev->fd = fd;
 	dev->dev = st.st_rdev;
+	dev->device_id = device_id;
 	wl_signal_init(&dev->events.change);
 	wl_list_insert(&session->devices, &dev->link);
 
 	return dev;
 
 error:
+	libseat_close_device(session->seat_handle, device_id);
 	free(dev);
 	close(fd);
 	return NULL;
@@ -214,7 +307,9 @@ error:
 
 void wlr_session_close_file(struct wlr_session *session,
 		struct wlr_device *dev) {
-	session->impl->close(session, dev->fd);
+	if (libseat_close_device(session->seat_handle, dev->device_id) == -1) {
+		wlr_log_errno(WLR_ERROR, "Failed to close device %d", dev->device_id);
+	}
 	wl_list_remove(&dev->link);
 	free(dev);
 }
@@ -223,8 +318,7 @@ bool wlr_session_change_vt(struct wlr_session *session, unsigned vt) {
 	if (!session) {
 		return false;
 	}
-
-	return session->impl->change_vt(session, vt);
+	return libseat_switch_session(session->seat_handle, vt) == 0;
 }
 
 /* Tests if 'path' is KMS compatible by trying to open it.