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

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Date:   Fri, 31 Aug 2018 10:21:39 -0600
From:   David Ahern <dsahern@...il.com>
To:     Lorenzo Bianconi <lorenzo.bianconi@...hat.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 10:19 AM, Lorenzo Bianconi wrote:
>> 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 

This is in init namespace
$ ip li set veth2 netns foo

$ ip monitor
Deleted 20: veth2@...h1: <BROADCAST,MULTICAST,M-DOWN> mtu 1500 qdisc
noop state DOWN group default
    link/ether c6:d0:d6:c5:23:7d brd ff:ff:ff:ff:ff:ff new-netns foo
new-ifindex 20

It shows the new namespace in the delete message.