netdev - Re: [RFC PATCH net-next] failover: allow name change on IFF

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Date:   Tue, 5 Mar 2019 19:36:18 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     si-wei liu <si-wei.liu@...cle.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        Sridhar Samudrala <sridhar.samudrala@...el.com>,
        Jakub Kicinski <kubakici@...pl>, Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org, liran.alon@...cle.com,
        boris.ostrovsky@...cle.com, vijay.balakrishna@...cle.com
Subject: Re: [RFC PATCH net-next] failover: allow name change on IFF_UP slave
 interfaces

On Tue, Mar 05, 2019 at 04:20:50PM -0800, si-wei liu wrote:
> 
> 
> On 3/5/2019 4:06 PM, Michael S. Tsirkin wrote:
> > On Tue, Mar 05, 2019 at 11:35:50AM -0800, si-wei liu wrote:
> > > 
> > > On 3/5/2019 11:24 AM, Stephen Hemminger wrote:
> > > > On Tue, 5 Mar 2019 11:19:32 -0800
> > > > si-wei liu <si-wei.liu@...cle.com> wrote:
> > > > 
> > > > > > I have a vague idea: would it work to *not* set
> > > > > > IFF_UP on slave devices at all?
> > > > > Hmm, I ever thought about this option, and it appears this solution is
> > > > > more invasive than required to convert existing scripts, despite the
> > > > > controversy of introducing internal netdev state to differentiate user
> > > > > visible state. Either we disallow slave to be brought up by user, or to
> > > > > not set IFF_UP flag but instead use the internal one, could end up with
> > > > > substantial behavioral change that breaks scripts. Consider any admin
> > > > > script that does `ip link set dev ... up' successfully just assumes the
> > > > > link is up and subsequent operation can be done as usual.
> > How would it work when carrier is off?
> > 
> > > While it *may*
> > > > > work for dracut (yet to be verified), I'm a bit concerned that there are
> > > > > more scripts to be converted than those that don't follow volatile
> > > > > failover slave names. It's technically doable, but may not worth the
> > > > > effort (in terms of porting existing scripts/apps).
> > > > > 
> > > > > Thanks
> > > > > -Siwei
> > > > Won't work for most devices.  Many devices turn off PHY and link layer
> > > > if not IFF_UP
> > > True, that's what I said about introducing internal state for those driver
> > > and other kernel component. Very invasive change indeed.
> > > 
> > > -Siwei
> > Well I did say it's vague.
> > How about hiding IFF_UP from dev_get_flags (and probably
> > __dev_change_flags)?
> > 
> Any different? This has small footprint for the kernel change for sure,
> while the discrepancy is still there. Anyone who writes code for IFF_UP will
> not notice IFF_FAILOVER_SLAVE.
> 
> Not to mention more userspace "fixup" work has to be done due to this
> change.
> 
> -Siwei
> 
> 

Point is it's ok since most userspace should just ignore slaves
- hopefully it will just ignore it since it already
ignores interfaces that are down.

-- 
MST