netdev - Re: [PATCH net-next] veth: report NEWLINK event when moving the peer device in a new namespace

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Message-ID: <20180831161902.GD6236@localhost.localdomain>
Date:   Fri, 31 Aug 2018 18:19:03 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
To:     David Ahern <dsahern@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] veth: report NEWLINK event when moving the peer
 device in a new namespace

> On 8/31/18 5:43 AM, Lorenzo Bianconi wrote:
> > When moving a veth device to another namespace, userspace receives a
> > RTM_DELLINK message indicating the device has been removed from current
> > netns. However, the other peer does not receive a netlink event
> > containing new values for IFLA_LINK_NETNSID and IFLA_LINK veth
> > attributes.
> > Fix that behaviour sending to userspace a RTM_NEWLINK message in the peer
> > namespace to report new IFLA_LINK_NETNSID/IFLA_LINK values
> > 
> 
> A newlink message is generated in the new namespace. What information is
> missing from that message?
> 

Hi David,

let's assume we have two veth paired devices (veth0 and veth1) on inet
namespace. When moving a veth1 to another namespace, userspace is notified
with RTM_DELLINK event on inet namespace to indicate that veth1 has been
moved to another namespace. However some userspace applications
(e.g. NetworkManager), listening for events on inet namespace, are interested
in veth1 ifindex in the new namespace. This patch sends a new RTM_NEWLINK event
in inet namespace to provide new values for IFLA_LINK_NETNSID/IFLA_LINK 

Regards,
Lorenzo