From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <stephen@networkplumber.org>
Subject: Re: [PATCH iproute2 1/3] vxcan,veth: Forbid "type" for peer device
Date: Tue, 26 Dec 2017 09:05:35 -0800
Message-ID: <20171226090535.51ac43ef@xeon-e3>
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Cc: netdev@vger.kernel.org
To: Serhey Popovych <serhe.popovych@gmail.com>
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On Wed, 20 Dec 2017 09:37:29 +0200
Serhey Popovych <serhe.popovych@gmail.com> wrote:

> It is already given for original device we configure this
> peer for.
> 
> Results from following command before/after change applied
> are shown below:
> 
>   $ ip link add dev veth1a type veth peer name veth1b \
>                            type veth peer name veth1c
> 
> Before:
> -------
> 
> <no output, no netdevs created>
> 
> After:
> ------
> 
> Error: argument "type" is wrong: not supported for peer
> 
> Signed-off-by: Serhey Popovych <serhe.popovych@gmail.com>

This makes a lot of sense.
Maybe the better error message would be to use duparg() since
that is the most likely cause of the user error.