From: Thomas Graf <tgraf@suug.ch>
Subject: Re: [PATCH 1/4] [NETLINK]: Handle NLM_F_ECHO in netlink_rcv_skb()
Date: Thu, 10 Aug 2006 21:02:10 +0200
Message-ID: <20060810190210.GH14627@postel.suug.ch>
References: <20060809204821.216122988@postel.suug.ch> <20060809205439.434010049@postel.suug.ch> <20060810155120.GA494@ms2.inr.ac.ru>
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Cc: davem@davemloft.net, netdev@vger.kernel.org
To: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
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* Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> 2006-08-10 19:51
> > This patch handles NLM_F_ECHO in netlink_rcv_skb() to
> > handle it in a central point. Most subsystems currently
> > interpret NLM_F_ECHO as to just unicast events to the
> > originator of the change while the real meaning of the
> > flag is to echo the request.
> 
> Do not you think it is useless to echo something back to originator,
> who just sent it?
> 
> Actually, the sense of NLM_F_ECHO was to tell user what happened due to
> his request. The answer is not original request, which can contain
> some incomplete fields etc., but full information about object
> deleted/added/changed. Moreover, the feedback can contain several
> messages (though accurately it is done only in net/sched/), f.e. when
> the request triggered deletion of one object and addition of another.
> 
> Obviously, it cannot be done in a central place.
> 
> Normally, it is not needed, "ip route add" does not tell user, what
> actually was done, so that it suppresses echo. But for multistage
> operation it is absolutely necessary: the answer contains f.e. auto-allocated
> handles, which should be given in subsequent requests.

What's wrong with listening to the notification for that purpose?