[openib-general] Specifying subnet prefix to OpenSM?

[Galen Shipman]

I have 2 test machines, each with two HCAs. One HCA on each node is  
plugged into a switch, the other two HCAs are connected back to back.
The goal is to get two different subnets, one for each pair of HCAs.  
Currently I am using "opensm --guid" in order to run OpenSM on the  
each HCA/Port 0. The problem is that I also want these two subnets to  
appear distinct in some fashion. I am querying the subnet via:

     ibv_query_gid(hca->ib_dev_context, port_num, 0, &gid);
     subnet = ntoh64(gid.global.subnet_prefix);


Not sure if this is the correct thing to do, but this is what I am  
doing ;-).

So, is there a way to specify the subnet prefix to OpenSM? Is there  
some other method that I can use to determine that the subnets are  
distinct?


Thanks,

Galen