netdev - Re: [PATCH net-next] net/smc: Introduce TCP ULP support

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Message-ID: <97ea52de-5419-22ee-7f55-b92887dcaada@linux.ibm.com>
Date:   Thu, 30 Dec 2021 16:03:19 +0100
From:   Karsten Graul <kgraul@...ux.ibm.com>
To:     Tony Lu <tonylu@...ux.alibaba.com>
Cc:     kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net-next] net/smc: Introduce TCP ULP support

On 28/12/2021 14:44, Tony Lu wrote:
> This implements TCP ULP for SMC, helps applications to replace TCP with
> SMC protocol in place. And we use it to implement transparent
> replacement.
> 
> This replaces original TCP sockets with SMC, reuse TCP as clcsock when
> calling setsockopt with TCP_ULP option, and without any overhead.

This looks very interesting. Can you provide a simple userspace example about 
how to use ULP with smc?

And how do you make sure that the in-band CLC handshake doesn't interfere with the
previous TCP traffic, is the idea to put some kind of protocol around it so both
sides 'know' when the protocol ended and the CLC handshake starts?