I am not certain but I believe this is what was intended, this I do know
authorRobert Garrett <rob@dragonflybsd.org>
Wed, 3 Sep 2003 23:51:48 +0000 (23:51 +0000)
committerRobert Garrett <rob@dragonflybsd.org>
Wed, 3 Sep 2003 23:51:48 +0000 (23:51 +0000)
commit630a348c46cd65e810bf8a4999bb66606461d2b7
treecf1b3d6fb17ef07198fb372b9294658b7f3233c6
parentd99a0cbecc6cc22bb2594cea653a4c582d465c0d
I am not certain but I believe this is what was intended, this I do know
it fixes the generic kernel build.

basically changed

-       events = ap_events &
+       events = ap->a_events &
sys/vfs/fifofs/fifo_vnops.c