netdev - Re: [PATCHv3 net-next] rtnetlink: Honour NLM_F_ECHO flag in rtnl

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Message-ID: <YzOz9ePdsIMGg0s+@Laptop-X1>
Date:   Wed, 28 Sep 2022 10:39:49 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Ido Schimmel <idosch@...dia.com>,
        Petr Machata <petrm@...dia.com>,
        Florent Fourcot <florent.fourcot@...irst.fr>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Guillaume Nault <gnault@...hat.com>,
        David Ahern <dsahern@...nel.org>
Subject: Re: [PATCHv3 net-next] rtnetlink: Honour NLM_F_ECHO flag in
 rtnl_{new, set, del}link

On Tue, Sep 27, 2022 at 07:21:30AM -0700, Jakub Kicinski wrote:
> On Tue, 27 Sep 2022 12:13:03 +0800 Hangbin Liu wrote:
> > @@ -3382,6 +3401,12 @@ static int rtnl_newlink_create(struct sk_buff *skb, struct ifinfomsg *ifm,
> >  		if (err)
> >  			goto out_unregister;
> >  	}
> > +
> > +	nskb = rtmsg_ifinfo_build_skb(RTM_NEWLINK, dev, 0, 0, GFP_KERNEL, NULL,
> > +				      0, pid, nlh->nlmsg_seq);
> > +	if (nskb)
> > +		rtnl_notify(nskb, dev_net(dev), pid, RTNLGRP_LINK, nlh, GFP_KERNEL);
> > +
> >  out:
> >  	if (link_net)
> >  		put_net(link_net);
> 
> I'm surprised you're adding new notifications. Does the kernel not
> already notify about new links? I thought rtnl_newlink_create() ->
> rtnl_configure_link() -> __dev_notify_flags() sends a notification,
> already.

I think __dev_notify_flags() only sends notification when dev flag changed.
On the other hand, the notification is sent via multicast, while this patch
is intend to unicast the notification to the user space.

Thanks
Hangbin