UDA driver query

[eichelbe at nadc.arpa]

---
Here's a problem that asks wizards to test out their long-term memory.
I have a VAX 11/780 under 4.1 BSD UNIX and I have a version of a supposedly
4.1 BSD UNIX uda.c (UDA50/RA81) driver that compiles but for one error.
In the routine udprobe (which is shown below) there is a reference to
a variable uh_lastiv in the uba_hd structure.  This structure is in the header
file /sys/h/ubavar.h, but I don't find a uh_lastiv in the structure.  Here come
the questions:
(1) What is uh_lastiv supposed to do?
(2) Can I (and how if I can) change udprobe to get rid of the uh_lastiv
    reference safely?
(3) If I can't get rid of the reference, how should I change the uba_hd
    structure in /sys/h/ubavar.h so I too can use uh_lastiv, and if I do this
    will I have to change any code anywhere else in the kernel, etc. ?
    (This last part, about changes to other code, is important since I am
     really at a loss here.  If someone could just do a grep for uh_lastiv
     through the system code if you have uh_lastiv in your /sys/h/ubavar.h.)
---
udprobe(reg, ctlr)
	caddr_t reg;
	int ctlr;
{
	register int br, cvec;
	register struct uda_softc *sc = &uda_softc[ctlr];

#ifdef lint
	br = 0; cvec = br; br = cvec;
#endif
	/* SHOULD CHECK THAT IT REALLY IS A UDA */
	br = 0x15;
	cvec = sc->sc_ivec = (uba_hd[numuba].uh_lastiv -= 4);
	return(1);
}
---
	Oh, and here's uba_hd, extracted from /sys/h/ubavar.h.
---
struct	uba_hd {
	struct	uba_regs *uh_uba;	/* virt addr of uba */
	struct	uba_regs *uh_physuba;	/* phys addr of uba */
	int	(**uh_vec)();		/* interrupt vector */
	struct	uba_device *uh_actf;	/* head of queue to transfer */
	struct	uba_device *uh_actl;	/* tail of queue to transfer */
	short	uh_mrwant;		/* someone is waiting for map reg */
	short	uh_bdpwant;		/* someone awaits bdp's */
	int	uh_bdpfree;		/* free bdp's */
	int	uh_hangcnt;		/* number of ticks hung */
	int	uh_zvcnt;		/* number of 0 vectors */
	short	uh_users;		/* transient bdp use count */
	short	uh_xclu;		/* an rk07 is using this uba! */
#define	UAMSIZ	25
	struct	map *uh_map;		/* buffered data path regs free */
};
---
	Thanks.
		Jon Eichelberger
		eichelbe at NADC.ARPA