Re: [PATCH net] rtnetlink: Restore RTM_NEW/DELLINK notification behavior

[Hangbin Liu <liuhangbin@gmail.com>]

On Tue, Apr 11, 2023 at 09:43:19AM +0200, Martin Willi wrote:
> The commits referenced below allows userspace to use the NLM_F_ECHO flag
> for RTM_NEW/DELLINK operations to receive unicast notifications for the
> affected link. Prior to these changes, applications may have relied on
> multicast notifications to learn the same information without specifying
> the NLM_F_ECHO flag.
> 
> For such applications, the mentioned commits changed the behavior for
> requests not using NLM_F_ECHO. Multicast notifications are still received,
> but now use the portid of the requester and the sequence number of the
> request instead of zero values used previously. For the application, this
> message may be unexpected and likely handled as a response to the
> NLM_F_ACKed request, especially if it uses the same socket to handle
> requests and notifications.
> 
> To fix existing applications relying on the old notification behavior,
> set the portid and sequence number in the notification only if the
> request included the NLM_F_ECHO flag. This restores the old behavior
> for applications not using it, but allows unicasted notifications for
> others.
> 
> Fixes: f3a63cce1b4f ("rtnetlink: Honour NLM_F_ECHO flag in rtnl_delete_link")
> Fixes: d88e136cab37 ("rtnetlink: Honour NLM_F_ECHO flag in rtnl_newlink_create")
> Signed-off-by: Martin Willi <martin@strongswan.org>

Not sure if the Fixes tag should be
1d997f101307 ("rtnetlink: pass netlink message header and portid to rtnl_configure_link()")

Others looks good to me.

Thanks
Hangbin