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

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Date:   Thu, 13 Apr 2023 10:48:03 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Martin Willi <martin@...ongswan.org>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Guillaume Nault <gnault@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net] rtnetlink: Restore RTM_NEW/DELLINK notification
 behavior

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@...ongswan.org>

Acked-by: Hangbin Liu <liuhangbin@...il.com>