GDirectoryModel: Automagically update on filesystem changes.

Use the new watch_file() mechanism to monitor the currently open directory
for changes and refresh the model when notified. This makes FileManager
automagically show newly added files. :^)

Libraries/LibGUI/GDirectoryModel.cpp

@@ -308,7 +308,18 @@ void GDirectoryModel::open(const StringView& a_path)
     if (!dirp)
         return;
     closedir(dirp);
+    if (m_notifier)
+        close(m_notifier->fd());
     m_path = path;
+    int watch_fd = watch_file(path.characters(), path.length());
+    if (watch_fd < 0) {
+        perror("watch_file");
+        ASSERT_NOT_REACHED();
+    }
+    m_notifier = make<CNotifier>(watch_fd, CNotifier::Event::Read);
+    m_notifier->on_ready_to_read = [this] {
+        update();
+    };
     update();
     set_selected_index(index(0, 0));
 }

Libraries/LibGUI/GDirectoryModel.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <AK/HashMap.h>
+#include <LibCore/CNotifier.h>
 #include <LibGUI/GModel.h>
 #include <sys/stat.h>
 
@@ -77,4 +78,6 @@ private:
 
     HashMap<uid_t, String> m_user_names;
     HashMap<gid_t, String> m_group_names;
+
+    OwnPtr<CNotifier> m_notifier;
 };