[libvirt] [PATCH 2/3] qemu: remove unnecessary setting of tap device online state

[Laine Stump]

On 08/25/2016 05:42 AM, Vasiliy Tolstov wrote:
>
> 25 Авг 2016 г. 12:34 пользователь Vasiliy Tolstov <v.tolstov at selfip.ru 
> <mailto:v.tolstov at selfip.ru>> написал:
> >
> > 25 Авг 2016 г. 8:58 пользователь "Laine Stump" <laine at laine.org 
> <mailto:laine at laine.org>> написал:
> > >
> > > The linkstate setting of an <interface> is only meant to change the
> > > online status reported to the guest system by the emulated network
> > > device driver in qemu,
> >
> I need to set host side status of interface. Without this live 
> migration with dinamic routing software (ospf with quagga or bird) 
> bring packet drops. Because on dest interface in up state and kernel 
> try to forward packets to it, but guest  CPU is not running.
>

That shouldn't be a problem, since the IPInfo isn't added to the tap 
device until immediately before the guest CPU is started on the 
destination (that's the purpose of qemuInterfaceStartDevice()).


> Also host side status needed for easy blackhole traffic to guest ip.
>

Is this something you need to do while the guest is already running? If 
not, then I think we don't need anything extra.


> May be create inside the source link state attribute for host side 
> link status? So it consistent with ip and route elements?
>

If necessary, that might be the right solution, although I still think 
it's better to not set the tap device offline, in case it's connected to 
a bridge - we wouldn't want to trigger an STP forward delay. Maybe just 
delete (and later re-add) the IPInfo would be less disruptive? (Or it 
might be *more* disruptive, we'd have to try both).


> >
> > > but when support for auto-creating tap devices
> > > for <interface type='ethernet'> was added in commit 9717d6, a chunk of
> > > code was also added to qemuDomainChangeNetLinkState() that sets the
> > > online status of the tap device (i.e. the *host* side of the
> > > interface) for type='ethernet'. This was never done for tap devices
> > > used in type='bridge' or type='network' interfaces, nor was it done in
> > > the past for tap devices created by external scripts for
> > > type='ethernet', so we shouldn't be doing it now.
> > >
> > > This patch removes the bit of code in qemuDomainChangeNetLinkState()
> > > that modifies online status of the tap device.
> > > ---
> > >  src/qemu/qemu_hotplug.c | 15 ---------------
> > >  1 file changed, 15 deletions(-)
> > >
> > > diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
> > > index 00e4a75..5300bc1 100644
> > > --- a/src/qemu/qemu_hotplug.c
> > > +++ b/src/qemu/qemu_hotplug.c
> > > @@ -2324,21 +2324,6 @@ int 
> qemuDomainChangeNetLinkState(virQEMUDriverPtr driver,
> > >      if (ret < 0)
> > >          goto cleanup;
> > >
> > > -    if (virDomainNetGetActualType(dev) == 
> VIR_DOMAIN_NET_TYPE_ETHERNET) {
> > > -        switch (linkstate) {
> > > -            case VIR_DOMAIN_NET_INTERFACE_LINK_STATE_UP:
> > > -            case VIR_DOMAIN_NET_INTERFACE_LINK_STATE_DEFAULT:
> > > -                if ((ret = virNetDevSetOnline(dev->ifname, true)) 
> < 0)
> > > -                    goto cleanup;
> > > -                break;
> > > -
> > > -            case VIR_DOMAIN_NET_INTERFACE_LINK_STATE_DOWN:
> > > -                if ((ret = virNetDevSetOnline(dev->ifname, 
> false)) < 0)
> > > -                    goto cleanup;
> > > -                break;
> > > -            }
> > > -    }
> > > -
> > >      /* modify the device configuration */
> > >      dev->linkstate = linkstate;
> > >
> > > --
> > > 2.7.4
> > >
>

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