netdev - Re: question about nla_nest

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Date:	Thu, 27 Jan 2011 18:25:36 +0100 (CET)
From:	Julia Lawall <julia@...u.dk>
To:	Kurt Van Dijck <kurt.van.dijck@....be>
Cc:	hadi@...erus.ca, netdev@...r.kernel.org
Subject: Re: question about nla_nest_cancel

On Thu, 27 Jan 2011, Kurt Van Dijck wrote:

> On Thu, Jan 27, 2011 at 06:08:34PM +0100, Julia Lawall wrote:
> > 
> > I find numerous occurrences of code like the following, in which nest ends 
> > up with the value NULL and then nla_nest_cancel is called with nest as the 
> > second argument.  But nla_nest_cancel just calls nlmsg_trim with the same 
> > second argument, and nlmsg_trim does nothing if its second argument is 
> > NULL.  Is there any reason to keep these calls?
> I just learned this:
> nla_nest_start() adds data to the skb.
> nla_nest_end() 'commits' the proper length.
> nla_nest_cancel() reverts skb to the state before nla_nest_start(),
> as if nothing happened.

Yes, I can see this as well.  But in this case, it seems to me taht 
nothing has happened, because nla_nest_star has returned NULL?

julia
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