Re: [PATCH v2] RDMA/CMA: fix iWARP adapter TCP port space usage

Steve Wise
2010-06-23T20:29:35Z

Steve Wise wrote:
> Jason Gunthorpe wrote:
>> On Wed, Jun 23, 2010 at 03:11:27PM -0500, Steve Wise wrote:
>>
>>> The IP address assigned for the cxgb3i iscsi device is _not_
>>> assigned to a netdev interface via ifconfig, as far as I understand
>>> it (by looking at the cxgb3i code). So the host stack doesn't know
>>> about this address. There is an administrative requirement, I
>>> assume, that the secret iscsi ipaddr is within a subnet that is
>>> bound to the T3 ethX interface. Otherwise the routing lookup
>>> wouldn't work.
>>>
>>
>> So who responds to neighbor queries, and how do outgoing queries get
>> sent with the right IP? Sounds odd...
>>
>>
>
> The iscsi hba is only an initiator, so it doesn't need to respond to
> arp queries. I guess the Source Protocol Address in the outgoing ARP
> request will be the ipaddr of the outgoing interface. Its ok though
> because what is needed is the next-hop peer's hwaddr. So the ARP
> reply comes in, updates the host neigh entry, and a NEIGH_EVENT
> callout is performed to the offload device drivers. It is a little
> hackish, but that's the only way the netdev maintainers would allow
> iscsi offload in. They originally tried to use the src address from
> the ethX interface for the offload iscsi connections and that was
> rejected.
>
>

In case you're interested...Here is the tail end of the cxgb3i original
submission thread showing the use of a "private IP address which is
unkown to the OS".