Put the following two lines in /etc/devfs/conf.d/mysymlink and run update-devfsd
and it will create and remove sym-links from /dev/floppy/0 to /dev/fd0.

REGISTER	^floppy/0$	MFUNCTION /usr/local/lib/mysymlink.so mysymlink $devname fd0
UNREGISTER	^floppy/0$	MFUNCTION /usr/local/lib/mysymlink.so myunlink fd0

Use the following two lines instead to achieve a similar effect through the
CFUNCTION interface.  However they will create and remove two links, /etc/fd0
and /dev/fd0u1440, the code can dynamically handle up to 4 sym-links.

REGISTER	^floppy/0$	CFUNCTION /usr/local/lib/mysymlink.so cfdolink EVENT fd0 fd0u1440
UNREGISTER	^floppy/0$	CFUNCTION /usr/local/lib/mysymlink.so cfdolink EVENT fd0 fd0u1440