[openib-general] [RFC] [PATCH v2] rdma/ib_cm: fix APM support

[Or Gerlitz]

Michael S. Tsirkin wrote:
> Quoting r. Sean Hefty <sean.hefty at intel.com>:
>> Subject: RE: [RFC] [PATCH v2] rdma/ib_cm: fix APM support
>>
>>> BTW, just to clarify, in CMA pieces are still missing for APM support.
>>> Is that right?
>> Correct - the CMA does not provide path failover capabilities.
>>
>> Is this something that you're wanting in the CMA?
> 
> Yes - I am hearing this is as a requirement from SDP.

Few comments on CMA / APM / fail-over:

to start with IB/APM is limited only to the case of both ports of the 
same HCA hence it does not provide general purpose solution for IB ULP 
HA, specifically costumers want to be protected against IB port / hca / 
cable / switch failure and APM does not address the hca case.

more over, the CMA API addressing is based on **IP** addresses, so when 
a client connects it provides the IP address of the server and 
optionally the its src IP as well. The IP2GID resolution is done by the 
the linux netstack ARP api and neighboring subsystem. I don't see a 
robust way within this framework to have a single destination IP being 
resolved to two destination GIDs. And i strongly disagree to stop using 
this framework.

Again, even with the second point being somehow solved, the apm nature 
makes it a very limited in power feature of IB.

Or.