netdev - Re: [PATCH] netlink: fix append of whole original message on negative ack.

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Message-ID: <20081023205543.GA19462@ioremap.net>
Date:	Fri, 24 Oct 2008 00:55:43 +0400
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	David Miller <davem@...emloft.net>
Cc:	michellammertink@...il.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] netlink: fix append of whole original message on negative ack.

Hi.

On Thu, Oct 23, 2008 at 01:45:13PM -0700, David Miller (davem@...emloft.net) wrote:
> > Netlink can return an negative acknowledgement, which AFAICT should include an error code and the whole original message. This patch fixes the size argument given to the __nlmsg_put call. Without this patch only the original header was attached.
> > ---
> > 
> > Can anyone explain to me why struct nlmsgerr contains an int error and the nlmsghdr struct. The comment in netlink_ack states that the whole message should be appended. Why not only include an int error in struct nlmsgerr and just append the original message?

Having header (even seq/pid only) is enough to find a message
for that userspace which cares. Looks like your patch can break
existing applications which are used to work with header only,
even if that was a mistake? Although application is supposed to
check the length, it still can expect only a header. I have to
note, that I do not know any such application though.

-- 
	Evgeniy Polyakov
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