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Message-ID: <20080827144122.GT20815@postel.suug.ch>
Date: Wed, 27 Aug 2008 16:41:22 +0200
From: Thomas Graf <tgraf@...g.ch>
To: Alexander Duyck <alexander.duyck@...il.com>
Cc: Stephen Hemminger <shemminger@...tta.com>,
Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
davem@...emloft.net, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
Alexander Duyck <alexander.h.duyck@...el.com>
Subject: Re: [PATCH] IPROUTE: correct nla nested message generated by netem_parse_opt
* Alexander Duyck <alexander.duyck@...il.com> 2008-08-21 19:37
> The problem is the current kernel ABI was changed in commit
> b9a2f2e450b0f770bb4347ae8d48eb2dea701e24 "netlink: Fix
> nla_parse_nested_compat() to call nla_parse() directly" to support a
> format that I have only seen generated in netem_parse_opt. The kernel
> and prio_parse_opt qdisc both generate the other format which includes
> the extra attribute header to contain the nested attributes. This
> patch fixes tc so that netem will use the correct nested attribute
> order for kernels prior to this commit and once this commit has been
> reverted.
How was it ever supposed to work? The code looked like the following
prior to commit b03f4672007e533c8dbf0965f995182586216bf1 which made
it used nla_parse_nested_compat()
- /* Handle nested options after initial queue options.
- * Should have put all options in nested format but too late now.
- */
- if (nla_len(opt) > sizeof(*qopt)) {
- struct nlattr *tb[TCA_NETEM_MAX + 1];
- if (nla_parse(tb, TCA_NETEM_MAX,
- nla_data(opt) + sizeof(*qopt),
- nla_len(opt) - sizeof(*qopt), NULL))
nla_parse_nested_compat() now does exactly what the above code does. So
in what way has the kernel ABI changed?
There is two ways of sending a fixed struct + attributes inside an
attribute:
a) (old and outdated method)
attr foo
fixed struct
[nested attr 1]
[nested attr 2]
This format can be parsed with nla_parse_nested_compat(attr foo)
b) (new method)
attr foo
fixed struct
attr container
[nested attr 1]
[nested attr 2]
This format is parsed with nla_parse_nested(attr container)
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