netdev - Re: [RFC] hv_netvsc: automatically name slave VF network device

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Message-ID: <20171219131816.70645a7b@cakuba.netronome.com>
Date:   Tue, 19 Dec 2017 13:18:16 -0800
From:   Jakub Kicinski <kubakici@...pl>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev@...r.kernel.org, Stephen Hemminger <sthemmin@...rosoft.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [RFC] hv_netvsc: automatically name slave VF network device

On Tue, 19 Dec 2017 12:44:25 -0800, Stephen Hemminger wrote:
> On Tue, 19 Dec 2017 12:32:34 -0800
> Jakub Kicinski <kubakici@...pl> wrote:
> 
> > On Tue, 19 Dec 2017 11:35:37 -0800, Stephen Hemminger wrote:  
> > > Rename the VF device to ethX_vf based on the ethX as the
> > > synthetic device.  This eliminates the need for delay on setup,
> > > and the PCI (udev based) naming is not reproducible on Hyper-V
> > > anyway. The name of the VF does not matter since all control
> > > operations take place the primary device. It does make the
> > > user experience better to associate the names.
> > > 
> > > Based on feedback from all.systems.go talk.
> > > The downside is that it requires exporting a symbol from netdev
> > > core which makes it harder to backport.
> > > 
> > > Signed-off-by: Stephen Hemminger <sthemmin@...rosoft.com>    
> > 
> > Why do you have to name the devices in the kernel space in the first
> > place? :/  Why don't upstream the correct change to biosdevname like
> > hardware vendors do?  
> 
> biosdevname is dead, gone and wouldn't work on Azure (it dumpster dives in /dev/mem).

Hm, I haven't worked on biosdevname myself, but AFAIU it also falls 
back to information from the PCI VPD, which could be populated by 
the hypervisor.

> I assume you mean the modern application is udev, and it works but the name is meaningless
> because it based of synthetic PCI information. The PCI host adapter is simulated
> for pass through devices. Names like enp12s0.
> 
> Since every passthrough VF device on Hyper-V/Azure has a matching synthetic
> network device with same mac address. It is best to have the relationship
> shown in the name.

How about we make the VF drivers expose "vf" as phys_port_name?
Then systemd/udev should glue that onto the name regardless of
how the VF is used.

> > Your VF setup is really _not_ special, I don't understand why we are 
> > OK with ignoring the standard practices.  Real enterprise distroes
> > are very careful never to break the naming of interfaces and they keep
> > the naming policy in user space.  Playing tricks in the kernel has every
> > chance of breaking existing user setups.  
> 
> Actually, Systemd folks said "naming policy is in userspace only because
> kernel can't get it right". Also there is no uniformity in userspace
> there are at least 5 systems trying to do network setup. And most of
> them depend on eth0 (yes still). Fixing userspace is impossible.