netdev - net_failover slave udev renaming (was Re: [RFC PATCH net-next v6 4/4] netvsc: refactor notifier/event handling code to use the bypass framework)

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Date:   Thu, 21 Feb 2019 17:14:44 -0800
From:   Siwei Liu <loseweigh@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        Sridhar Samudrala <sridhar.samudrala@...el.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        virtio-dev <virtio-dev@...ts.oasis-open.org>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Jakub Kicinski <kubakici@...pl>,
        Jason Wang <jasowang@...hat.com>, liran.alon@...cle.com,
        si-wei liu <si-wei.liu@...cle.com>
Subject: net_failover slave udev renaming (was Re: [RFC PATCH net-next v6 4/4]
 netvsc: refactor notifier/event handling code to use the bypass framework)

Sorry for replying to this ancient thread. There was some remaining
issue that I don't think the initial net_failover patch got addressed
cleanly, see:

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1815268

The renaming of 'eth0' to 'ens4' fails because the udev userspace was
not specifically writtten for such kernel automatic enslavement.
Specifically, if it is a bond or team, the slave would typically get
renamed *before* virtual device gets created, that's what udev can
control (without getting netdev opened early by the other part of
kernel) and other userspace components for e.g. initramfs,
init-scripts can coordinate well in between. The in-kernel
auto-enslavement of net_failover breaks this userspace convention,
which don't provides a solution if user care about consistent naming
on the slave netdevs specifically.

Previously this issue had been specifically called out when IFF_HIDDEN
and the 1-netdev was proposed, but no one gives out a solution to this
problem ever since. Please share your mind how to proceed and solve
this userspace issue if netdev does not welcome a 1-netdev model.

On Wed, Apr 11, 2018 at 12:53 AM Jiri Pirko <jiri@...nulli.us> wrote:
>
> Tue, Apr 10, 2018 at 11:26:08PM CEST, stephen@...workplumber.org wrote:
> >On Tue, 10 Apr 2018 11:59:50 -0700
> >Sridhar Samudrala <sridhar.samudrala@...el.com> wrote:
> >
> >> Use the registration/notification framework supported by the generic
> >> bypass infrastructure.
> >>
> >> Signed-off-by: Sridhar Samudrala <sridhar.samudrala@...el.com>
> >> ---
> >
> >Thanks for doing this.  Your current version has couple show stopper
> >issues.
> >
> >First, the slave device is instantly taking over the slave.
> >This doesn't allow udev/systemd to do its device rename of the slave
> >device. Netvsc uses a delayed work to workaround this.
>
> Wait. Why the fact a device is enslaved has to affect the udev in any
> way? If it does, smells like a bug in udev.

See above for clarifications.

Thanks,

>
>
> >
> >Secondly, the select queue needs to call queue selection in VF.
> >The bonding/teaming logic doesn't work well for UDP flows.
> >Commit b3bf5666a510 ("hv_netvsc: defer queue selection to VF")
> >fixed this performance problem.
> >
> >Lastly, more indirection is bad in current climate.
> >
> >I am not completely adverse to this but it needs to be fast, simple
> >and completely transparent.