Re: [PATCH 1/4] [NETLINK]: Handle NLM_F_ECHO in netlink_rcv_skb()

[Thomas Graf <tgraf@suug.ch>]

Hello

* Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> 2006-08-11 00:32
> Nothing! NLM_F_ECHO _is_ listening for notifications without subscription
> to multicast groups and need to figure out what messages are yours.
> But beyond this NLM_F_ECHO is totally subset of this.
> Which still makes much more sense then echoing of a know thing, does not it?

I get your point and I see the value. Unfortunately, probably due to
lack of documentation, this feature isn't used by any applications I
know of. We even put in the hacks to make identification of own caused
notifications easier by storing the netlink pid of the originator in
the notification message.

I will put this back in (document it! :) and hide it behind
nlmsg_notify() so we do it for all notifications for consistency.

I use echoing of the original request for debuging purposes, it allows
to verify what is actually being parsed at the netlink family specific
parsing function. Using libnl a flag enables NLM_F_ECHO in all messages
and it gets simple to verify what exactly is being seen in the kernel side
parser by looking at the messages log. I agree, there is no functional
value besides the possibility to implement a netlink ping with NLMSG_NOOP.