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

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Date:   Fri, 30 Aug 2019 08:47:41 -0600
From:   David Ahern <dsahern@...il.com>
To:     Roopa Prabhu <roopa@...ulusnetworks.com>,
        Michal Kubecek <mkubecek@...e.cz>
Cc:     netdev <netdev@...r.kernel.org>, Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>, dcbw@...hat.com,
        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 8/30/19 8:35 AM, Roopa Prabhu wrote:
> On Wed, Aug 28, 2019 at 10:26 PM Michal Kubecek <mkubecek@...e.cz> wrote:
>>
>> On Wed, Aug 28, 2019 at 09:36:41PM -0700, Roopa Prabhu wrote:
>>>
>>> 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 )
>>
>> AFAICS rtnl_dellink() calls nlmsg_parse_deprecated() so that even
>> current code would ignore any future attribute in RTM_DELLINK message
>> (any kernel before the strict validation was introduced definitely will)
>> and it does not seem to check NLM_F_APPEND or NLM_F_UPDATE either. So
>> unless I missed something, such message would result in deleting the
>> network device (if possible) with any kernel not implementing the
>> feature.
> 
> ok, ack. yes today it does. I was hinting if that can be changed to
> support list update with a flag like the RTM_DELLINK AF_BRIDGE does
> for vlan list del.
> 
> so to summarize, i think we have discussed the following options to
> update a netlink list attribute so far:
> (a) encode an optional attribute/flag in the list attribute in
> RTM_SETLINK to indicate if it is a add or del

The ALT_IFNAME attribute could also be a struct that has both the string
and a flag.

> (b) Use a flag in RTM_SETLINK and RTM_DELINK to indicate add/del
> (close to bridge vlan add/del)
> (c) introduce a separate generic msg type to add/del to a list
> attribute (IIUC this does need a separate msg type per subsystem or
> netlink API)
>