linux-kernel - Re: [PATCH net] net/smc: use the correct ndev to find pnetid by pnetid table

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Message-ID: <20250114130747.77a56d9a.pasic@linux.ibm.com>
Date: Tue, 14 Jan 2025 13:07:47 +0100
From: Halil Pasic <pasic@...ux.ibm.com>
To: Guangguan Wang <guangguan.wang@...ux.alibaba.com>
Cc: Paolo Abeni <pabeni@...hat.com>, wenjia@...ux.ibm.com, jaka@...ux.ibm.com,
        alibuda@...ux.alibaba.com, tonylu@...ux.alibaba.com,
        guwen@...ux.alibaba.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, horms@...nel.org, linux-rdma@...r.kernel.org,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Alexandra Winter <wintera@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH net] net/smc: use the correct ndev to find pnetid by
 pnetid table

On Fri, 10 Jan 2025 13:43:44 +0800
Guangguan Wang <guangguan.wang@...ux.alibaba.com> wrote:

> > I think I showed a valid and practical setup that would break with your
> > patch as is. Do you agree with that statement?  
> Did you mean
> "
> Now for something like a bond of two OSA
> interfaces, I would expect the two legs of the bond to probably have a
> "HW PNETID", but the netdev representing the bond itself won't have one
> unless the Linux admin defines a software PNETID, which is work, and
> can't have a HW PNETID because it is a software construct within Linux.
> Breaking for example an active-backup bond setup where the legs have
> HW PNETIDs and the admin did not bother to specify a PNETID for the bond
> is not acceptable.
> " ?
> If the legs have HW pnetids, add pnetid to bond netdev will fail as
> smc_pnet_add_eth will check whether the base_ndev already have HW pnetid.
> 
> If the legs without HW pnetids, and admin add pnetids to legs through smc_pnet.
> Yes, my patch will break the setup. What Paolo suggests(both checking ndev and
> base_ndev, and replace || by && )can help compatible with the setup.

I'm glad we agree on that part. Things are much more acceptable if we
are doing both base and ndev. Nevertheless I would like to understand
your problem better, and talk about it to my team. I will also ask some
questions in another email.

That said having things work differently if there is a HW PNETID on
the base, and different if there is none is IMHO wonky and again
asymmetric.

Imagine the following you have your nice little setup with a PNETID on
a non-leaf and a base_ndev that has no PNETID. Then your HW admin
configures a PNETID to your base_ndev, a different one. Suddenly
your ndev PNETID is ignored for reasons not obvious to you. Yes it is
similar to having a software PNETID on the base_ndev and getting it
overruled by a HW PNETID, but much less obvious IMHO. I also think
a software PNETID of the base should probably take precedence over over
the software pnetid of ndev.

Regards,
Halil