/usr/src/linux-source-3.13.0/debian.master/d-i/modules/multipath-modules is in linux-source-3.13.0 3.13.0-27.50.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | dm-multipath ?
dm-round-robin ?
|