On Wed, Aug 28, 2019 at 10:26 PM Michal Kubecek [off-list ref] wrote:

On Wed, Aug 28, 2019 at 09:36:41PM -0700, Roopa Prabhu wrote:

quoted

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
(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)