util: add helper APIs for dealing with inotify in portable manner

The inotify userspace API for reading events is quite horrible, so it is
useful to wrap it in a more friendly API to avoid duplicating code
across many users in QEMU. Wrapping it also allows introduction of a
platform portability layer, so that we can add impls for non-Linux based
equivalents in future.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

util/filemonitor-stub.c

@@ -0,0 +1,59 @@
+/*
+ * QEMU file monitor stub impl
+ *
+ * Copyright (c) 2018 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/filemonitor.h"
+#include "qemu/error-report.h"
+#include "qapi/error.h"
+
+
+QFileMonitor *
+qemu_file_monitor_new(Error **errp)
+{
+    error_setg(errp, "File monitoring not available on this platform");
+    return NULL;
+}
+
+
+void
+qemu_file_monitor_free(QFileMonitor *mon G_GNUC_UNUSED)
+{
+}
+
+
+int
+qemu_file_monitor_add_watch(QFileMonitor *mon G_GNUC_UNUSED,
+                            const char *dirpath G_GNUC_UNUSED,
+                            const char *filename G_GNUC_UNUSED,
+                            QFileMonitorHandler cb G_GNUC_UNUSED,
+                            void *opaque G_GNUC_UNUSED,
+                            Error **errp)
+{
+    error_setg(errp, "File monitoring not available on this platform");
+    return -1;
+}
+
+
+void
+qemu_file_monitor_remove_watch(QFileMonitor *mon G_GNUC_UNUSED,
+                               const char *dirpath G_GNUC_UNUSED,
+                               int id G_GNUC_UNUSED)
+{
+}