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