Re: netlink, RTM_NEWTCLASS, nested attributes

[Denys Fedoryshchenko]

On 2013-02-21 01:21, Stephen Hemminger wrote:
> On Tue, 19 Feb 2013 23:45:25 +0200
> Denys Fedoryshchenko <denys@xxxxxxxxxxx> wrote:
>
> > 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?
>
> Several legacy netlink interfaces don't use NESTED flag. These are by
> now enshrined in ABI and can't change. In code, that uses libmnl, I 
> just
> manually clear the flag as needed and document why. This could
> be added to libmnl.

Thank you for clarification!

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