Add a hack to fail registration of kq events on a non-ufs filesystem, as

support for those is non-existent at the moment.

sys/kern/vfs_vnops.c

@@ -669,6 +669,14 @@ filt_vnattach(struct knote *kn)
 	    kn->kn_fp->f_type != DTYPE_FIFO)
 		return (EBADF);
 
+	/*
+	 * XXX
+	 * this is a hack simply to cause the filter attach to fail
+	 * for non-ufs filesystems, until the support for them is done.
+	 */
+	if ((vp)->v_tag != VT_UFS)
+		return (EOPNOTSUPP);
+
 	vp = (struct vnode *)kn->kn_fp->f_data;
 
         simple_lock(&vp->v_pollinfo.vpi_lock);