changes to cam_xpt to support sequential scanning (!parallel)

[Scott Long]

Matt Jacob wrote:

> One solution that Scott suggested to some of the negotiation issues for
> the MPT was to not do parallel problem, i.e., all targets in parallel.
> 
> The patch at http://people.freebsd.org/~mjacob/CAM_PATCHES_FOR_SEQSCAN
> 
> does just that and I've had quite good success with it so far. I add
> a new flat, PIM_SEQSCAN, which cases xpt_scan_bus to *not* scan all
> targets in parallel but rather to scan them sequentially.
> 
> Comments?
> 
> The code also does some cleanups under failure conditions.
> 
> After a bit more testing I'd like to put this in if there are no
> objections so I can get the mpt U320 stuff off my back for a while.

I think that this is a good idea.  It's a shame that we have to emulate
Windows and Linux behaviour, but if it's needed then it's needed.  Good
job getting it figured out.

Scott