GtkFileChooser: How to get names of files that are inside subfolders?

[Phong Cao <phngcv gmail com>]

Hello everybody,

I am trying to develop a music manager that lets the users import all audio
files from a folder. That folder may contain many subfolders, and each
subfolder may contain many files. I know that I need to create a
GtkFileChooser Dialog with GTK_FILE_CHOOSER_ACTION_SELECT_FOLDER enabled so
that the user can choose folders instead of files.

However, I do not know how to make this GtkFileChooser selects/imports all
the files available in that directory (not only the files that are shown in
the GtkFileChooser but the files that are deeply contained inside
subfolders).

Thank you for reading my questions! I hope you guys have a good day!