[ofa-general] librdmacm feature request

[Steve Wise]

Just thinking out loud:

What if each cm_id has its own fd?  Then they could be associated with a 
channel, which is just an object that tracks which fds are in the 
channel and uses select()/poll() on the entire set of fds for 
rdma_get_cm_event().

So moving a cm_id to another channel is simple and doesn't involve 
moving the events since they will be queued on the cm_id's fd. You just 
move the fd from one channel to another and events keep flowing as normal...

Steve.


Sean Hefty wrote:
> The only idea I've been able to come up with for moving an rdma_cm_id 
> between fd's is to perform a two-step process.  (The two steps would be 
> done by a single API call.)
> 
> 1. prepare to modify(old_fd, rdma_cm_id)
>    Somehow mark that the rdma_cm_id will migrate to a new fd.
> 2. commit modify(new_fd, rdma_cm_id)
>    Migrates the rdma_cm_id to the new fd and moves the events.
> 
> Using two steps provides the kernel code the file context that it needs, 
> and should protect against the fd's being closed.  The biggest hurdle to 
> this is ensuring that the same user owns both fd's, possibly by 
> validating some sort of key between the two steps.  I just haven't 
> figured out what works as a key.
> 
> - Sean
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