Most Linux distros symbolically link /dev/fd to /proc/self/fd for
compatibility with other unix-like systems. On Linux this is a subdirectory
containing one entry for each file which the reading the directory process
has open, named by its file descriptor, and which is a symbolic link to the
actual file.
On FreeBSD we have a bit similar interface - fdescfs(5). Unlike Linux opening
our /dev/fd/X (as the most unix-like systems) gives a duplicate of the file
descriptor while on Linux gives a new file. Also fdescfs(5) does not provide
readlink method.

At least newest bash and rm depends on /dev/fd, so add readlink method to
the fdescfs(5).