[openib-general] [PATCH] [CM] add private data comparison to match REQs with listens

[Sean Hefty]

Sean Hefty wrote:
> As an update: further testing revealed that there is an issue with this 
> implementation that is also found in the original code.  The issue deals 
> with how listen requests that rely on a data mask are inserted and 
> located in the red/black tree.  I'm trying to come up with a fix for this.

After researching into this, I'm coming to the conclusion that there does not 
exist an efficient way to sort/search for listens without adding some restrictions.

For example, a client listens on id1 with mask1.  A request is matched with the 
listen if its serviceid & mask1 = id1.  If a second client listens on id2 with 
mask2, then a request must check against both requests for a match, or until a 
match is found.  There's no method that I can find that can be used to filter 
checks that works in a generic fashion, resulting in requests needing to walk a 
linear list of listens.  There are several potential fixes for this, with only a 
couple mentioned below.

One solution around this is to have the IB CM only listen on service IDs, and 
remove the mask parameter from the API.  This requires SDP to change to only 
listen on ports that have a listener.

Another alternative is to restrict the type of masks that are supported.  If 
masks are restricted to a series of most significant bits, then the existing 
algorithm can be used.  For instance, we can support masks 0xFF00 and 0xFFF0, 
but not 0x00FF or 0xFF0F.  This restriction would work for both SDP and the CMA. 
  To be clear, the API could change from a mask to the number of bits to match.

Matching on private data can either be done by clients, or restrictions can be 
placed on it as well.  For private data, I believe that a restriction that all 
listen requests on the same service ID use the same mask is sufficient.

Hopefully this makes sense to people.  Thoughts?

- Sean