netdev - netlink, RTM_NEWTCLASS, nested attributes

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Date:	Tue, 19 Feb 2013 23:45:25 +0200
From:	Denys Fedoryshchenko <denys@...p.net.lb>
To:	<netdev@...r.kernel.org>, <pablo@...filter.org>,
	<jhs@...atatu.com>, <davem@...emloft.net>,
	<linux-kernel@...r.kernel.org>
Subject: netlink, RTM_NEWTCLASS, nested attributes

Hi

I tried recently to write my own tool based on amazing libmnl (which 
makes understanding of netlink - easy), written
by Pablo Neira Ayuso, to manage QoS in Linux and faced problem, which i 
think probably
a bug in handling netlink messages in kernel.

For example if i send message, RTM_NEWTCLASS, after attribute 
TCA_OPTIONS i have nested attributes,
for example in HTB: TCA_HTB_PARMS, TCA_HTB_RTAB, TCA_HTB_CTAB.
libmnl, if i use nested attribute, adding a bit to it, by OR -  
NLA_F_NESTED(1 << 15).
If i remove this flag - everything works fine. And here is the case, 
iproute2 tools
just update length of TCA_OPTIONS, without setting flag, and it works 
because of that fine too.

So there is basically 3 solutions:
1)New function in libmnl to do nested attributes without setting by OR 
flag
2)AND-ing attribute type in kernel to ignore nested flag
3)Keeping as is, who cares?

Thank you for your attention.

---
Denys Fedoryshchenko, Network Engineer, Virtual ISP S.A.L.
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