fdserver is used by programs to register file descriptors so they can be shared with other processes in the system. The file descriptors are sent to fdserver through ancilliary data to a UNIX domain socket, and can be requested in a similar fashion. See fdserver.h for the list of functions available to applications, and the examples directory.
The initial implementation of fdserver is found in ODP's code, see odp_fdserver.c.
autoreconf --install
./configure
make
Optionally make check