vop_balloc
DO_OPS(ops, error, &ap, vop_balloc);
DO_OPS(ap->a_head.a_ops, error, ap, vop_balloc);
vop_balloc(*(vp)->v_ops, vp, offset, size, cred, flags, bpp)
int (*vop_balloc)(struct vop_balloc_args *);
int vop_balloc(struct vop_ops *ops, struct vnode *vp, off_t startoffset,
.vop_balloc = ffs_balloc,