netdev - Re: [net-next PATCH] net: rtnetlink: Enslave device before bringing it up

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Message-ID: <20190529172158.GE31548@orbyte.nwl.cc>
Date:   Wed, 29 May 2019 19:21:58 +0200
From:   Phil Sutter <phil@....cc>
To:     David Ahern <dsahern@...il.com>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [net-next PATCH] net: rtnetlink: Enslave device before bringing
 it up

On Wed, May 29, 2019 at 09:41:07AM -0600, David Ahern wrote:
> On 5/29/19 7:51 AM, Phil Sutter wrote:
> > Unlike with bridges, one can't add an interface to a bond and set it up
> > at the same time:
> > 
> > | # ip link set dummy0 down
> > | # ip link set dummy0 master bond0 up
> > | Error: Device can not be enslaved while up.
> > 
> > Of all drivers with ndo_add_slave callback, bond and team decline if
> > IFF_UP flag is set, vrf cycles the interface (i.e., sets it down and
> > immediately up again) and the others just don't care.
> > 
> > Support the common notion of setting the interface up after enslaving it
> > by sorting the operations accordingly.
> > 
> > Signed-off-by: Phil Sutter <phil@....cc>
> > ---
> >  net/core/rtnetlink.c | 14 +++++++-------
> >  1 file changed, 7 insertions(+), 7 deletions(-)
> > 
> 
> I agree with the intent - enslave before up.
> 
> Not sure how likely this is, but it does break the case:
> ip li set dummy0 master bond0 down

That's right. I could allow for that by ordering the enslave and state
change dynamically, but doubt it's worth the effort. Instead of the
above I'd rather expect 'ip l s d0 nomaster down' to be a more common
use-case (which is not affected by my patch).

Thanks, Phil