Re: [PATCH rdma-next 4/4] IB/core: Add IP to GID netlink offload

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Wed, May 04, 2016 at 06:41:58PM +0300, Leon Romanovsky wrote:
> From: Mark Bloch <markb-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> 
> There is an assumption that rdmacm is used only between nodes
> in the same IB subnet, this why ARP resolution can be used to turn
> IP to GID in rdmacm.
> 
> When dealing with IB communication between subnets this assumption
> is no longer valid. ARP resolution will get us the next hop device
> address and not the peer node's device address.
> 
> To overcome this limitation, let's check user space if it can
> provide the GID of the peer node, and fail if not.
> 
> We add a sequence number to identify each request and fill in the GID
> upon answer from user space.

This description doesn't describe what this patch is trying to do.

This patch is delegating IP to GID translation to user space if there
is a route table entry for the destination.

I have to say, I really don't like this at all. If we want to have
proper routing support then the translation needs to be done somehow
in-band. What is user space supposed to do?

Jason
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