isp(4) doppleganger disk devices

[Ade Lovett]

Hi folks,

I have a number of JBODs that have a bunch of SATA drives in them,  
presented to the outside world as 2*FCAL connectors, hooked up to a  
Qlogic 2312 HBA.

The first issue I had was that each of the 16 drives in the bay  
presented themselves on each of luns 0-31 during the initial loop  
scan, resulting in 1024 'da' devices, which, when it came later on to  
attach, confused the system somewhat -- of course, it also meant the  
machine took over 30 minutes to boot, being attached to a slow serial  
console.  This was hackable by forcibly setting isp->isp_maxluns to 1,  
rather than the existing code which set maxluns based on the type of  
hardware.

This ensured that each disk was only seen once (on lun 0), but still  
resulted in each of the 16 drives being presented to the FreeBSD box  
on both of the channels of Qlogic card.  Not unreasonable in and of  
itself, given the potential for multipathing, but since that doesn't  
appear to work -- dinking first with daX, then daY, which correspond  
to the same drive, but on isp0 and isp1, results in somewhat  
entertaining behavior, we decided to go for a simple hack to hide  
certain devices on a per-controller basis, presenting the first half  
of the array only on channel 0, and the second on channel 1.

With revision 1.113.2.4 (RELENG_6) of sys/dev/isp/isp.c, this was  
achieved with the following patch:

@@ -2474,2 +2492,8 @@
                 fcp->portdb[i].portid = fcp->tport[loopid].portid;
+
+               /* XXX: Supernews */
+               if (isp_ignore_target(isp, i)) {
+                       fcp->portdb[i].valid = 0;
+                       continue;
+               }
                 fcp->portdb[i].valid = 1;

and a suitably defined local isp_ignore_target() function that grabbed  
the device unit and target number and said 'yay' or 'nay'.  With a  
convenient device.hints, I ended up with the first half of the array  
being presented as da10-da17 on isp0, and the second half as da20-27  
on isp1.

Attempts to do this with the new isp(4) driver have proven  
unsuccessful so far (mainly down to my lack of full understanding of  
the new code).  I realize of course that what I'm trying to accomplish  
is the result of, at best, iffy hardware, but nonetheless, is there a  
way to solve this as I currently have it, or an alternate approach  
that I haven't thought about?

Help!

-aDe