[ofa-general] Re: [Query] ib add path record cache

[Sean Hefty]

> You'd need to use a vendor class 2 if you wanted to use RMPP as the SA
> does. However, there is some rearranging you would need to do if you
> compare the relevant MAD formats.

Reading into the spec more, it seems our current choice is limited to 
using a vendor class.  Application classes are controlled by the IBTA. 
Of the two vendor classes, class 2 clearly defines that RMPP is used, 
but also adds the OUI field to the MAD.  This throws off using the SA 
MAD class format.  I see a few possibilities:

Use vendor class 1:
There's no restriction on the MAD data.  This would allow us to match 
the SA MAD class format exactly.  The drawback is that we need to modify 
the MAD layer to identify the class as using RMPP.

Use vendor class 2:
Reading the spec, it looks like a reserved field in the MAD header is 
reserved even if using a vendor defined class.  If this is the proper 
interpretation, then we either need to shift the SA data down 4-8 bytes, 
or we drop the first 4 bytes of the SM_Key.

If we ever want to do more than simple path record caching, I think 
we'll want the full SM_Key.  Between the remaining choices, my 
preference would be to adapt a class 1 for our purpose.  Anyone else 
have thoughts on this?

- Sean