linux: Use inhibitor lock to guard poll pausing

Use an inhibitor lock obtained via logind to make sure the polling
is paused before the system is put to sleep, rather than racing with
the suspension.

https://bugs.freedesktop.org/show_bug.cgi?id=99763

src/linux/Makefile.am

@@ -9,6 +9,7 @@ AM_CPPFLAGS = \
 	-I$(top_srcdir)/libupower-glib				\
 	$(USB_CFLAGS)						\
 	$(GIO_CFLAGS)						\
+	$(GIO_UNIX_CFLAGS)					\
 	$(GUDEV_CFLAGS)						\
 	$(POLKIT_CFLAGS)					\
 	$(GLIB_CFLAGS)						\
@@ -56,7 +57,9 @@ hidpp_test_SOURCES =						\
 hidpp_test_LDADD =						\
 	-lm							\
 	$(GLIB_LIBS)						\
-	$(GIO_LIBS)
+	$(GIO_LIBS)						\
+	$(GIO_UNIX_LIBS)
+
 hidpp_test_CFLAGS = $(AM_CFLAGS) $(WARNINGFLAGS_C)
 
 EXTRA_DIST = $(libupshared_la_SOURCES) 			\

src/linux/up-backend.c

@@ -27,6 +27,7 @@
 #include <sys/wait.h>
 #include <glib/gi18n.h>
 #include <gio/gio.h>
+#include <gio/gunixfdlist.h>
 #include <gudev/gudev.h>
 
 #include "up-backend.h"
@@ -63,6 +64,7 @@ struct UpBackendPrivate
 	UpConfig		*config;
 	GDBusProxy		*logind_proxy;
 	guint                    logind_sleep_id;
+	int                      logind_inhibitor_fd;
 };
 
 enum {
@@ -460,6 +462,78 @@ up_backend_take_action (UpBackend *backend)
 			   NULL);
 }
 
+/**
+ * up_backend_inhibitor_lock_take:
+ * @backend: The %UpBackend class instance
+ *
+ * Acquire a sleep 'delay lock' via systemd's logind that will
+ * inhibit going to sleep until the lock is released again via
+ * up_backend_inhibitor_lock_release().
+ * Does nothing if the lock was already acquired.
+ */
+static void
+up_backend_inhibitor_lock_take (UpBackend *backend)
+{
+	GVariant *out, *input;
+	GUnixFDList *fds;
+	GError *error = NULL;
+
+	if (backend->priv->logind_inhibitor_fd > -1) {
+		return;
+	}
+
+	input = g_variant_new ("(ssss)",
+			       "sleep",                /* what */
+			       "UPower",               /* who */
+			       "Pause device polling", /* why */
+			       "delay");               /* mode */
+
+	out = g_dbus_proxy_call_with_unix_fd_list_sync (backend->priv->logind_proxy,
+							"Inhibit",
+							input,
+							G_DBUS_CALL_FLAGS_NONE,
+							-1,
+							NULL,
+							&fds,
+							NULL,
+							&error);
+	if (out == NULL) {
+		g_warning ("Could not acquire inhibitor lock: %s", error->message);
+		return;
+	}
+
+	if (g_unix_fd_list_get_length (fds) != 1) {
+		g_warning ("Unexpected values returned by logind's 'Inhibit'");
+		g_variant_unref (out);
+		return;
+	}
+
+	backend->priv->logind_inhibitor_fd = g_unix_fd_list_get (fds, 0, NULL);
+	g_variant_unref (out);
+
+	g_debug ("Acquired inhibitor lock (%i)", backend->priv->logind_inhibitor_fd);
+}
+
+/**
+ * up_backend_inhibitor_lock_release:
+ * @backend: The %UpBackend class instance
+ *
+ * Releases a previously acquired inhibitor lock or does nothing
+ * if no lock is held;
+ */
+static void
+up_backend_inhibitor_lock_release (UpBackend *backend)
+{
+	if (backend->priv->logind_inhibitor_fd == -1) {
+		return;
+	}
+
+	close (backend->priv->logind_inhibitor_fd);
+	backend->priv->logind_inhibitor_fd = -1;
+
+	g_debug ("Released inhibitor lock");
+}
+
 /**
  * up_backend_prepare_for_sleep:
  *
@@ -493,9 +567,12 @@ up_backend_prepare_for_sleep (GDBusConnection *connection,
 
 	if (will_sleep) {
 		up_daemon_pause_poll (backend->priv->daemon);
+		up_backend_inhibitor_lock_release (backend);
 		return;
 	}
 
+	up_backend_inhibitor_lock_take (backend);
+
 	/* we are waking up, lets refresh all battery devices */
 	g_debug ("Woke up from sleep; about to refresh devices");
 	array = up_device_list_get_array (backend->priv->device_list);
@@ -570,6 +647,9 @@ up_backend_init (UpBackend *backend)
 						       backend,
 						       NULL);
 	backend->priv->logind_sleep_id = sleep_id;
+	backend->priv->logind_inhibitor_fd = -1;
+
+	up_backend_inhibitor_lock_take (backend);
 }
 
 /**
@@ -597,6 +677,8 @@ up_backend_finalize (GObject *object)
 	g_dbus_connection_signal_unsubscribe (bus,
 					      backend->priv->logind_sleep_id);
 
+	up_backend_inhibitor_lock_release (backend);
+
 	g_clear_object (&backend->priv->logind_proxy);
 
 	g_object_unref (backend->priv->managed_devices);