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

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Message-ID: <4339aaa1-f2aa-4454-b5b1-6ffb6415f484@linux.alibaba.com>
Date: Mon, 10 Feb 2025 19:16:57 +0800
From: Guangguan Wang <guangguan.wang@...ux.alibaba.com>
To: Halil Pasic <pasic@...ux.ibm.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>
Subject: Re: [PATCH net] net/smc: use the correct ndev to find pnetid by
 pnetid table



On 2025/1/15 19:53, Guangguan Wang wrote:
> 
> 
> On 2025/1/14 20:07, Halil Pasic wrote:
>> 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. 
> It is also acceptable for me.
> 
>> 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.
> Questions are welcome.
> 
>>
>> 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 am wondering if there are any scenarios that require setting different
> pnetids for different net devices in one netdev hierarchy. If no, maybe
> we should limit that only one pnetid can be set to one netdev hierarchy.
> 
>> I also think
>> a software PNETID of the base should probably take precedence over over
>> the software pnetid of ndev.
> Agree!
> 
> Thanks,
> Guangguan Wang
>>
>> Regards,
>> Halil

Hi Halil,

Are there any questions or further discussions about this patch? If no, I will
send a v2 patch, in which software pnetid will be searched in both base_ndev and ndev,
and base_ndev will take precedence over ndev.

Thanks,
Guangguan Wang