[openib-general] RFC userspace CMA

[Sean Hefty]

Tom Tucker wrote:
>>Something that didn't make sense for the kernel rdma_cm running over IB was 
>>adding a backlog parameter to the listen request.  (The IB CM is callback 
>>driven, so there's not really a backlog.)  I will probably add this to the 
>>userspace API.  Does iWarp need a backlog parameter in the kernel?
> 
> It is needed by some adapters. For the AMSO1100 it's passed down to the
> adapter to reserve syn cache entries for incoming connections. 

There's no problem adding this.  It just that for IB, the user can control the 
backlog themselves, which gives a little more flexibility.  I suppose we can 
define it as the maximum number of unacknowledged connection requests that a 
user can have.  Where acknowledging a connection request is done by accepting or 
rejecting the connection.  I'll work on adding this after getting the userspace 
CMA up.

> Yes it's funky. Basically, the listen in this context is the combination
> of a 'bind' and a 'listen'. If you specify 0 for a port number on bind,
> the stack will allocate one for you. 

I need to think about this more.  I'm not sure how to handle a bind of 0 over 
IB.  Can you handle this on the bind only, as opposed to listen?

- Sean