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 21:36:41 -0700
From:   Roopa Prabhu <roopa@...ulusnetworks.com>
To:     Jiri Pirko <jiri@...nulli.us>
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

On Wed, Aug 28, 2019 at 12:07 AM Jiri Pirko <jiri@...nulli.us> wrote:
>
> 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.

yes, so far it was not needed.
No other future possible examples in mind...but I wont be surprised if
we see such cases in the future.
Having a consistent API to extend a list attribute will help.

>
>
> >
> >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).

yes,  correct. I mentioned that because I was wondering if we can
think along the same lines for this API.
eg
(a) RTM_NEWLINK always replaces the list attribute
(b) RTM_SETLINK with NLM_F_APPEND always appends to the list attribute
(c) RTM_DELLINK with NLM_F_APPEND updates the list attribute

(It could be NLM_F_UPDATE if NLM_F_APPEND sounds weird in the del
case. I have not looked at the full dellink path if it will work
neatly..its been a busy day )


>
>
> >
> >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?

This seems fine but it does introduce a new type. If we can avoid a
new msg type with a flag that would be nice (like the NLM_F_APPEND eg
above).
The reason for that is to see if we can use it else where too (eg some
random future list attribute in the route subsystem. If a flag works
then we don't have to add a RTM_NEWROUTE variant of CMD SETLISTS and
CMD DELLISTS)