netdev - Re: [PATCH] Ipvlan should return an error when an address is already in use.

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Message-Id: <20170101.222632.843875843588487678.davem@davemloft.net>
Date:   Sun, 01 Jan 2017 22:26:32 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     kjlx@...pleofstupid.com
Cc:     maheshb@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH] Ipvlan should return an error when an address is
 already in use.

From: Krister Johansen <kjlx@...pleofstupid.com>
Date: Fri, 30 Dec 2016 20:10:58 -0800

> The ipvlan code already knows how to detect when a duplicate address is
> about to be assigned to an ipvlan device.  However, that failure is not
> propogated outward and leads to a silent failure.  This teaches the ip
> address addition functions how to report this error to the user
> applications so that a notifier chain failure during ip address addition
> will not appear to succeed when it actually has not.
> 
> This can be especially useful if it is necessary to provision many
> ipvlans in containers.  The provisioning software (or operator) can use
> this to detect situations where an ip address is unexpectedly in use.
> 
> Signed-off-by: Krister Johansen <kjlx@...pleofstupid.com>

Your patch isn't handling the case of primary address promotions,
which also issue NETDEV_UP events on these notifier chains.

But on a more basic level, it's extremely important that once you
start using the notifier_{from,to}_errno() handling for a notifier,
you must start doing so for all such cases of that notifier.