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Date:   Mon, 25 Sep 2023 13:50:22 +0200
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Subject: Re: [PATCH net-next v4 09/18] net/smc: introduce SMC-D loopback
 device
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To:     Wen Gu <guwen@linux.alibaba.com>, kgraul@linux.ibm.com,
        wenjia@linux.ibm.com, jaka@linux.ibm.com, davem@davemloft.net,
        edumazet@google.com, kuba@kernel.org, pabeni@redhat.com
Cc:     schnelle@linux.ibm.com, gbayer@linux.ibm.com, pasic@linux.ibm.com,
        alibuda@linux.alibaba.com, tonylu@linux.alibaba.com,
        dust.li@linux.alibaba.com, linux-s390@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
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 <1695568613-125057-10-git-send-email-guwen@linux.alibaba.com>
From:   Alexandra Winter <wintera@linux.ibm.com>
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On 24.09.23 17:16, Wen Gu wrote:
> This patch introduces a kind of loopback device for SMC-D. The device
> is created when SMC module is loaded and destroyed when the SMC module
> is unloaded. The loopback device is a kernel device used only by the
> SMC module and is not restricted by net namespace, so it can be used
> for local inter-process or inter-container communication.
> 
> Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
> ---
>  net/smc/Kconfig        |  13 ++++
>  net/smc/Makefile       |   2 +-
>  net/smc/af_smc.c       |  12 +++-
>  net/smc/smc_loopback.c | 165 +++++++++++++++++++++++++++++++++++++++++++++++++
>  net/smc/smc_loopback.h |  33 ++++++++++
>  5 files changed, 223 insertions(+), 2 deletions(-)
>  create mode 100644 net/smc/smc_loopback.c
>  create mode 100644 net/smc/smc_loopback.h


Hello Wen Gu,

thank you for adding the Kconfig, so the distributions can decide when to offer this feature.

I propose you add some kind of runtime switch as well. Not every user who loads the SMC module
may want to exploit smcd-loopback. Especially in native environements without containers.

If no RoCE interfaces or no ISM interfaces exist, the respective handling is skipped in SMC.
If loopback is always created unconditionally, there is no way to opt-out.