Re: [PATCH RFC net-next] net: Allow name change of IFF_UP interfaces

Eric Dumazet [off-list ref] writes:

On Thu, 2017-08-10 at 10:41 +0200, Vitaly Kuznetsov wrote:

quoted

Andrew Lunn [off-list ref] writes:

quoted

quoted

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 ?

We are - rtnetlink_event() does the job. We, however, don't have a
special IFLA_EVENT_* for name change and end up with IFLA_EVENT_NONE.

If yes, your patch is fine.

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

Yes but AFAIU daemons may need to do the same refresh when the interface
is down too (and, hopefully, they do it already).

-- 
  Vitaly