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

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Date:   Thu, 29 Aug 2019 07:26:20 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     netdev@...r.kernel.org
Cc:     Roopa Prabhu <roopa@...ulusnetworks.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        David Ahern <dsahern@...il.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 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.

Michal