netdev - Re: [PATCH net] failover: eliminate callback hell

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Date:   Fri, 8 Jun 2018 18:29:33 -0700
From:   Jakub Kicinski <kubakici@...pl>
To:     Siwei Liu <loseweigh@...il.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jiri Pirko <jiri@...nulli.us>, kys@...rosoft.com,
        haiyangz@...rosoft.com, David Miller <davem@...emloft.net>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        Netdev <netdev@...r.kernel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>
Subject: Re: [PATCH net] failover: eliminate callback hell

On Fri, 8 Jun 2018 16:44:12 -0700, Siwei Liu wrote:
> >> I have a somewhat different view regarding IFF_HIDDEN. The purpose of
> >> that flag, as well as the 1-netdev model, is to have a means to
> >> inherit the interface name from the VF, and to eliminate playing hacks
> >> around renaming devices, customizing udev rules and et al. Why
> >> inheriting VF's name important? To allow existing config/setup around
> >> VF continues to work across kernel feature upgrade. Most of network
> >> config files in all distros are based on interface names. Few are MAC
> >> address based but making lower slaves hidden would cover the rest. And
> >> most importantly, preserving the same level of user experience as
> >> using raw VF interface once getting all ndo_ops and ethtool_ops
> >> exposed. This is essential to realize transparent live migration that
> >> users dont have to learn and be aware of the undertaken.  
> >
> > Inheriting the VF name will fail in the migration scenario.
> > It is perfectly reasonable to migrate a guest to another machine where
> > the VF PCI address is different. And since current udev/systemd model
> > is to base network device name off of PCI address, the device will change
> > name when guest is migrated.
> >  
> The scenario of having VF on a different PCI address on post migration
> is essentially equal to plugging in a new NIC. Why it has to pair with
> the original PV? A sepearte PV device should be in place to pair the
> new VF.

IMHO it may be a better idea to look at the VF as acceleration for the
PV rather than PV a migration vehicle from the VF.  Hence we should
continue to follow the naming of PV, like the current implementation
does implicitly by linking to PV's struct device.