netdev - Re: [PATCH RFC net-next] net: Allow name change of IFF

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Message-ID: <1502355817.4936.9.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 10 Aug 2017 02:03:37 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Andrew Lunn <andrew@...n.ch>, network dev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH RFC net-next] net: Allow name change of IFF_UP interfaces

On Thu, 2017-08-10 at 10:41 +0200, Vitaly Kuznetsov wrote:
> Andrew Lunn <andrew@...n.ch> writes:
> 
> >> I understand the 'legacy' concern but at the same time we don't want to
> >> have aftificial limitations too. Name change, in particular, doesn't
> >> happen 'under the hood' -- someone privileged enough needs to request
> >> the change.
> >> 
> >> Can you think of any particular real world scenarios which are broken by
> >> the change?
> >
> > How about:
> >
> > man 8 dhclient-script
> >
> > The interface name is passed in $interface to the scripts. Do we get
> > the old name or the new name? I suspect scripts are going to break if
> > they are given the old name, which no longer exists.
> 
> Yes but why would anyone change interface name while dhclient-script is
> running? Things will also go wrong if you try bringing interface down
> during the run or do some other configuration, right? Running multiple
> configuration tools at the same moment is a bad idea, you never know
> what you're gonna end up with. 
> 
> As I see it, checks in kernel we have are meant to protect kernel
> itself, not to disallow all user<->kernel interactions leading to
> imperfect result.
> 
> (AFAIU) If we remove the check nothing is going to change: udev will
> still be renaming interfaces before bringing them up. In netvsc case
> users are not supposed to configure the VF interface at all, it just
> becomes a slave of netvsc interface.

Are we sending an event if device name is changed ?

If yes, your patch is fine.

If not, daemons would not be aware the need to refresh their view of the
world.