netdev - Re: [patch net-next rfc 3/7] net: rtnetlink: add commands to add and delete alternative ifnames

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Date:   Wed, 28 Aug 2019 09:07:11 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        David Ahern <dsahern@...il.com>,
        netdev <netdev@...r.kernel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>, dcbw@...hat.com,
        Michal Kubecek <mkubecek@...e.cz>,
        Andrew Lunn <andrew@...n.ch>, parav@...lanox.com,
        Saeed Mahameed <saeedm@...lanox.com>,
        mlxsw <mlxsw@...lanox.com>
Subject: Re: [patch net-next rfc 3/7] net: rtnetlink: add commands to add and
 delete alternative ifnames

Tue, Aug 27, 2019 at 05:14:49PM CEST, roopa@...ulusnetworks.com wrote:
>On Tue, Aug 27, 2019 at 2:35 AM Jiri Pirko <jiri@...nulli.us> wrote:
>>
>> Tue, Aug 27, 2019 at 10:22:42AM CEST, davem@...emloft.net wrote:
>> >From: Jiri Pirko <jiri@...nulli.us>
>> >Date: Tue, 27 Aug 2019 09:08:08 +0200
>> >
>> >> Okay, so if I understand correctly, on top of separate commands for
>> >> add/del of alternative names, you suggest also get/dump to be separate
>> >> command and don't fill this up in existing newling/getlink command.
>> >
>> >I'm not sure what to do yet.
>> >
>> >David has a point, because the only way these ifnames are useful is
>> >as ways to specify and choose net devices.  So based upon that I'm
>> >slightly learning towards not using separate commands.
>>
>> Well yeah, one can use it to handle existing commands instead of
>> IFLA_NAME.
>>
>> But why does it rule out separate commands? I think it is cleaner than
>> to put everything in poor setlink messages :/ The fact that we would
>> need to add "OP" to the setlink message just feels of. Other similar
>> needs may show up in the future and we may endup in ridiculous messages
>> like:
>>
>> SETLINK
>>   IFLA_NAME eth0
>>   IFLA_ATLNAME_LIST (nest)
>>       IFLA_ALTNAME_OP add
>>       IFLA_ALTNAME somereallylongname
>>       IFLA_ALTNAME_OP del
>>       IFLA_ALTNAME somereallyreallylongname
>>       IFLA_ALTNAME_OP add
>>       IFLA_ALTNAME someotherreallylongname
>>   IFLA_SOMETHING_ELSE_LIST (nest)
>>       IFLA_SOMETHING_ELSE_OP add
>>       ...
>>       IFLA_SOMETHING_ELSE_OP del
>>       ...
>>       IFLA_SOMETHING_ELSE_OP add
>>       ...
>>
>> I don't know what to think about it. Rollbacks are going to be pure hell :/
>
>I don't see a huge problem with the above. We need a way to solve this
>anyways for other list types in the future correct ?.
>The approach taken by this series will not scale if we have to add a
>new msg type and header for every such list attribute in the future.

Do you have some other examples in mind? So far, this was not needed.


>
>A good parallel here is bridge vlan which uses RTM_SETLINK and
>RTM_DELLINK for vlan add and deletes. But it does have an advantage of
>a separate
>msg space under AF_BRIDGE which makes it cleaner. Maybe something
>closer to that  can be made to work (possibly with a msg flag) ?.

1) Not sure if AF_BRIDGE is the right example how to do things
2) See br_vlan_info(). It is not an OP-PER-VLAN. You either add or
delete all passed info, depending on the cmd (RTM_SETLINK/RTM_DETLINK).


>
>Would be good to have a consistent way to update list attributes for
>future needs too.

Okay. Do you suggest to have new set of commands to handle
adding/deleting lists of items? altNames now, others (other nests) later?

Something like:

CMD SETLISTS
     IFLA_NAME eth0
     IFLA_ATLNAME_LIST (nest)
       IFLA_ALTNAME somereallylongname
       IFLA_ALTNAME somereallyreallylongname
       IFLA_ALTNAME someotherreallylongname
     IFLA_SOMETHING_ELSE_LIST (nest)
       IFLA_SOMETHING_ELSE
       IFLA_SOMETHING_ELSE
       IFLA_SOMETHING_ELSE


CMD DELLISTS
     IFLA_NAME eth0
     IFLA_ATLNAME_LIST (nest)
       IFLA_ALTNAME somereallylongname
       IFLA_ALTNAME somereallyreallylongname
       IFLA_ALTNAME someotherreallylongname
     IFLA_SOMETHING_ELSE_LIST (nest)
       IFLA_SOMETHING_ELSE
       IFLA_SOMETHING_ELSE
       IFLA_SOMETHING_ELSE

How does this sound?