Re: [dpdk-dev] [RFT] net/netvsc: initialize link state

[Mohammed Gamal <mgamal@redhat.com>]

On Fri, 2020-02-07 at 08:12 -0800, Stephen Hemminger wrote:
> On Fri, 07 Feb 2020 15:22:23 +0200
> Mohammed Gamal <mgamal@redhat.com> wrote:
> 
> > On Thu, 2020-02-06 at 16:10 -0800, Stephen Hemminger wrote:
> > > If application is using link state interrupt, the correct link
> > > state
> > > needs to be filled in when device is started. This is similar to
> > > how virtio updates link information.
> > > 
> > > Reported-by: Mohammed Gamal <mgamal@redhat.com>
> > > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > > ---
> > > This version marked RFT because am in airport without access to a
> > > machine to test it.
> > > 
> > >  drivers/net/netvsc/hn_ethdev.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/drivers/net/netvsc/hn_ethdev.c
> > > b/drivers/net/netvsc/hn_ethdev.c
> > > index c79f924379fe..564620748daf 100644
> > > --- a/drivers/net/netvsc/hn_ethdev.c
> > > +++ b/drivers/net/netvsc/hn_ethdev.c
> > > @@ -823,6 +823,10 @@ hn_dev_start(struct rte_eth_dev *dev)
> > >  	if (error)
> > >  		hn_rndis_set_rxfilter(hv, 0);
> > >  
> > > +	/* Initialize Link state */
> > > +	if (error == 0)
> > > +		hn_dev_link_update(dev, 0);
> > > +
> > >  	return error;
> > >  }
> > >    
> > 
> > I tested this and I always get the link status as UP, regardless of
> > whether I start the interface on the guest in UP or DOWN state.
> > Looking
> > at hn_dev_link_update() code, I see that the link status depends on
> > the
> > NDIS status that the driver gets from the host if my understanding
> > is
> > correct.
> > The question is whether if I use 'ip li set dev $IF_NAME down' on
> > the
> > guest affects the status the host sees, or would the host set the
> > state
> > to NDIS_MEDIA_STATE_CONNECTED of the device is physcially connected
> > regardless of what the guest tries to do?
> > 
> 
> Are you confused about admin state vs link state?  Admin state is the
> up/down state in software, and link state is the (virtual) hardware
> link
> status.  In traditional Linux, admin state is controlled by ip link
> set up/down; in DPDK the admin state is implied by whether the DPDK
> device is started or stopped.  The link state for hardware devices is
> determined by whether the hardware link has synchronized with the
> switch.
> In virtual environments this is synchronized. In Linux link state
> is reported as NOCARRIER (IFF_RUNNING). In DPDK it is reported in
> via the link info get.
> 
> The device visible to the kernel is the accelerated networking
> (Mellanox)
> device and is not related directly to the netvsc device.
> 
> To test link up/down is not easy on Azure. You would have to use
> Azure CLI
> to disconnect the NIC from VM.  On native Hyper-V you can test by
> setting up a virtual switch with an external network device; then
> unplug the network device.
> 
> 

I see. Thanks for the explanation. In this case this does work as
expected.

Tested-by: Mohammed Gamal <mgamal@redhat.com>