An action block that lists mounted storage media/volumes.
The fiber will pause until the listing has completed.
Since Android 5, removable SD cards, USB drives and other kind of storage volumes are usually
accessible through, i.e. “mounted” in, the
/storage directory, but the directory
itself is inaccessible and can’t be listed by regular apps due to lack of file permissions.
Note! Android 4.4 and lower don’t officially support removable storage and therefore only list primary external storage.