Merge branch 'speed-up-query-exists' into 'main'

gio: Add a query_exists vfunc to GFile

See merge request GNOME/glib!4272

gio/gfile.c

@@ -1192,8 +1192,11 @@ g_file_enumerate_children_finish (GFile         *file,
  * @cancellable: (nullable): optional #GCancellable object,
  *   %NULL to ignore
  *
- * Utility function to check if a particular file exists. This is
+ * Utility function to check if a particular file exists.
- * implemented using g_file_query_info() and as such does blocking I/O.
+ *
+ * The fallback implementation of this API is using [method@Gio.File.query_info]
+ * and therefore may do blocking I/O. To asynchronously query the existence
+ * of a file, use [method@Gio.File.query_info_async].
  *
  * Note that in many cases it is [racy to first check for file existence](https://en.wikipedia.org/wiki/Time_of_check_to_time_of_use)
  * and then execute something based on the outcome of that, because the
@@ -1222,10 +1225,16 @@ gboolean
 g_file_query_exists (GFile        *file,
                      GCancellable *cancellable)
 {
+  GFileIface *iface;
   GFileInfo *info;
 
   g_return_val_if_fail (G_IS_FILE (file), FALSE);
 
+  iface = G_FILE_GET_IFACE (file);
+
+  if (iface->query_exists)
+    return iface->query_exists (file, cancellable);
+
   info = g_file_query_info (file, G_FILE_ATTRIBUTE_STANDARD_TYPE,
                             G_FILE_QUERY_INFO_NONE, cancellable, NULL);
   if (info != NULL)

gio/gfile.h

@@ -148,6 +148,7 @@ typedef struct _GFileIface    		GFileIface;
  * @measure_disk_usage: Recursively measures the disk usage of @file. Since 2.38
  * @measure_disk_usage_async: Asynchronously recursively measures the disk usage of @file. Since 2.38
  * @measure_disk_usage_finish: Finishes an asynchronous recursive measurement of the disk usage of @file. Since 2.38
+ * @query_exists: Queries whether a file exists. Since 2.84
  *
  * An interface for writing VFS file handles.
  **/
@@ -598,6 +599,9 @@ struct _GFileIface
                                                        guint64                       *num_dirs,
                                                        guint64                       *num_files,
                                                        GError                       **error);
+
+  gboolean            (* query_exists)                (GFile                         *file,
+                                                       GCancellable                  *cancellable);
 };
 
 GIO_AVAILABLE_IN_ALL

gio/glocalfile.c

@@ -1259,6 +1259,17 @@ g_local_file_query_info (GFile                *file,
   return info;
 }
 
+#ifdef HAVE_FACCESSAT
+static gboolean
+g_local_file_query_exists (GFile        *file,
+                           GCancellable *cancellable)
+{
+  GLocalFile *local = G_LOCAL_FILE (file);
+
+  return faccessat (0, local->filename, F_OK, AT_EACCESS | AT_SYMLINK_NOFOLLOW) == 0;
+}
+#endif
+
 static GFileAttributeInfoList *
 g_local_file_query_settable_attributes (GFile         *file,
 					GCancellable  *cancellable,
@@ -3142,6 +3153,9 @@ g_local_file_file_iface_init (GFileIface *iface)
   iface->monitor_dir = g_local_file_monitor_dir;
   iface->monitor_file = g_local_file_monitor_file;
   iface->measure_disk_usage = g_local_file_measure_disk_usage;
+#ifdef HAVE_FACCESSAT
+  iface->query_exists = g_local_file_query_exists;
+#endif
 
   iface->supports_thread_contexts = TRUE;
 }

gio/gresourcefile.c

@@ -657,6 +657,15 @@ g_resource_file_set_display_name (GFile         *file,
   return NULL;
 }
 
+static gboolean
+g_resource_file_query_exists (GFile        *file,
+                              GCancellable *cancellable)
+{
+  GResourceFile *resource = G_RESOURCE_FILE (file);
+
+  return g_resources_get_info (resource->path, 0, NULL, NULL, NULL);
+}
+
 static void
 g_resource_file_file_iface_init (GFileIface *iface)
 {
@@ -683,6 +692,7 @@ g_resource_file_file_iface_init (GFileIface *iface)
   iface->query_writable_namespaces = g_resource_file_query_writable_namespaces;
   iface->read_fn = g_resource_file_read;
   iface->monitor_file = g_resource_file_monitor_file;
+  iface->query_exists = g_resource_file_query_exists;
 
   iface->supports_thread_contexts = TRUE;
 }

meson.build

@@ -683,6 +683,7 @@ functions = [
   'endmntent',
   'endservent',
   'epoll_create1',
+  'faccessat',
   'fallocate',
   'fchmod',
   'fchown',