Re: [PATCH v6 01/26] IB/Verbs: Implement new callback query_transport()

[Dave Goodell (dgoodell)]

On Apr 28, 2015, at 1:14 AM, Hefty, Sean <sean.hefty@xxxxxxxxx> wrote:

>>> Keep in mind that this enum was Liran's response to Michael's original
>>> patch.  In the enum in Michael's patch, there was both USNIC and
>>> USNIC_UDP.
>> 
>> Right! That's why I'm confused. Seems wrong to drop it, right?
> 
> I think the original USNIC protocol is layered directly over Ethernet.  The protocol basically stole an Ethertype (the one used for IBoE/RoCE) and implemented a proprietary protocol instead.  I have no idea how you resolve that, but I also don't think it's used anymore.  USNIC_UDP is just UDP.

Sean is correct. The legacy RDMA_TRANSPORT_USNIC code used a proprietary protocol over plain Ethernet frames.  The newer RDMA_TRANSPORT_USNIC_UDP code is just standard UDP/IP/Ethernet packets exposed to user space via the uverbs stack.  The current kernel module will support both formats, it just depends on which user space requests at create_qp time.  From the kernel point of view there is no common protocol between the two TRANSPORTs (other than sharing partially similar Ethernet frames at L2).

I posted last week to clarify some of this: http://marc.info/?l=linux-rdma&m=142972177830718&w=2

>> Well, if RoCEv2 uses the same protocol enum, that may introduce new
>> confusion, for example there will be some new CM handling for UDP encap,
>> source port selection, and of course vlan/tag assignment, etc. But if
>> there is support under way, and everyone is clear, then, ok.
> 
> RoCEv2/IBoUDP shares the same port space as UDP.  It has a similar issues as iWarp does sharing state with the main network stack.  I'm not aware of any proposal for resolving that.  Does it require using a separate IP address?  Does it use a port mapper function?  Does netdev care for UDP?  I'm not sure what USNIC does for this either, but a common solution between USNIC and IBoUDP seems reasonable.

Is the concern here about CM issues or the UDP ports used by the actual usNIC RQs?  CM is not used/supported for usNIC at this time.

-Dave

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