netdev - Re: question about nla_nest

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Message-ID: <Pine.LNX.4.64.1101271918250.13796@pc-004.diku.dk>
Date:	Thu, 27 Jan 2011 19:18:35 +0100 (CET)
From:	Julia Lawall <julia@...u.dk>
To:	Ben Pfaff <blp@...stanford.edu>
Cc:	hadi@...erus.ca, netdev@...r.kernel.org
Subject: Re: question about nla_nest_cancel

On Thu, 27 Jan 2011, Ben Pfaff wrote:

> Julia Lawall <julia@...u.dk> writes:
> 
> > 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 think that you are missing that NLA_PUT() contains an internal
> "goto nla_put_failure;".  If that branch is taken, then
> nla_nest_cancel() trims off the nested attribute.  So just
> removing the call to nla_nest_cancel() would change behavior in
> that case.

Indeed.  Thank you for the explanation.

julia
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