a string containing the attribute's name
a string containing the attribute's new value
a #GFileQueryInfoFlags
optional #GCancellable object, %NULL to ignore
%TRUE if the @attribute was successfully set to @value in the @file, %FALSE otherwise.
GException on failure.
Sets @attribute of type %G_FILE_ATTRIBUTE_TYPE_BYTE_STRING to @value. If @attribute is of a different type, this operation will fail, returning %FALSE.
If @cancellable is not %NULL, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error %G_IO_ERROR_CANCELLED will be returned.