netdev - Re: [PATCH net-next 0/1] netvsc: another VF datapath fix

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Date:   Tue, 8 Aug 2017 08:29:27 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        devel@...uxdriverproject.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 0/1] netvsc: another VF datapath fix

On Tue, 08 Aug 2017 17:24:03 +0200
Vitaly Kuznetsov <vkuznets@...hat.com> wrote:

> Stephen Hemminger <stephen@...workplumber.org> writes:
> 
> > On Tue, 08 Aug 2017 16:03:56 +0200
> > Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
> >  
> >> Stephen Hemminger <stephen@...workplumber.org> writes:
> >>   
> >> > Previous fix was incomplete.
> >> >    
> >> 
> >> Not really related to this patch series (which btw fixes my issue,
> >> thanks!), but I found one addition issue. Systemd fails to rename VF
> >> interface:
> >> 
> >>  kernel: mlx4_core 0002:00:02.0 eth2: joined to eth1
> >>  kernel: hv_netvsc 33b7a6f9-6736-451f-8fce-b382eaa50bee eth1: VF registering: eth2
> >>  kernel: hv_netvsc 33b7a6f9-6736-451f-8fce-b382eaa50bee eth1: Data path switched to VF: eth2
> >>  kernel: mlx4_en: eth2: Link Up
> >>  NetworkManager[750]: <info>  [1502200557.0821] device (eth2): link connected
> >>  NetworkManager[750]: <info>  [1502200557.1004] manager: (eth2): new Ethernet device (/org/freedesktop/NetworkManager/Devices/6)
> >>  systemd-udevd[6942]: Error changing net interface name 'eth2' to 'enP2p0s2': Device or resource busy
> >>  systemd-udevd[6942]: could not rename interface '6' from 'eth2' to 'enP2p0s2': Device or resource busy
> >> 
> >> With some debug added I figured out what's wrong: __netvsc_vf_setup()
> >> does dev_open() which sets IFF_UP flag on the interface. When systemd
> >> tries to rename the interface we get into dev_change_name() and this
> >> fails with -EBUSY when (dev->flags & IFF_UP).
> >> 
> >> The issue is of less importance as we're not supposed to configure VF
> >> interface now. However, we may still want to get a stable name for it.
> >> 
> >> Any idea how this can be fixed?  
> >
> > The problem is Network Manager should ignore the VF device. I don't run NM on these
> > interfaces because it causes more issues than it helps (dueling userspace).
> >
> > The driver needs to have slave track the master interface. Relying on userspace
> > to bring interface up leads to all the issues the bonding script had.
> >
> > One option would be to delay the work of bringing up the slave device to allow
> > small window for renaming to run.  
> 
> Actually, I tried removing 'if (dev->flags & IFF_UP)' check from
> dev_change_name() and everything seems to work fine. The history of this
> code predates git so I have no idea why it's forbiden to change names of
> IFF_UP interfaces... I can send an RFC removing the check to figure out
> the truth :-)

That only works because NM by default brings everything up.
Many users don't use NM on servers.