netdev - Re: [PATCH RFC 3/3] RDMA/siw: Require non-zero 6-byte MACs for soft iWARP

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Date: Fri, 5 May 2023 20:03:01 +0000
From: Chuck Lever III <chuck.lever@...cle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
CC: Chuck Lever <cel@...nel.org>,
        "open list:NETWORKING [GENERAL]"
	<netdev@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Bernard
 Metzler <BMT@...ich.ibm.com>, Tom Talpey <tom@...pey.com>
Subject: Re: [PATCH RFC 3/3] RDMA/siw: Require non-zero 6-byte MACs for soft
 iWARP



> On May 5, 2023, at 3:58 PM, Jason Gunthorpe <jgg@...pe.ca> wrote:
> 
> On Fri, May 05, 2023 at 11:43:11AM -0400, Chuck Lever wrote:
>> From: Chuck Lever <chuck.lever@...cle.com>
>> 
>> In the past, LOOPBACK and NONE (tunnel) devices had all-zero MAC
>> addresses. siw_device_create() would fall back to copying the
>> device's name in those cases, because an all-zero MAC address breaks
>> the RDMA core IP-to-device lookup mechanism.
> 
> Why not just make up a dummy address in SIW? It shouldn't need to leak
> out of it.. It is just some artifact of how the iWarp stuff has been
> designed

I've been trying that.

Even though the siw0 device is now registered with a non-zero GID, 
cma_acquire_dev_by_src_ip() still comes up with a zero GID which
matches no device. Address resolution then fails.

I'm still looking into why.


--
Chuck Lever