Proposed F19 Feature: systemd/udev Predictable Network Interface Names

[Andy Gospodarek]

On Mon, Mar 04, 2013 at 10:19:14AM -0600, Matt Domsch wrote:
> On Mon, Mar 04, 2013 at 10:03:01AM -0600, Andy Gospodarek wrote:
> > On Mon, Mar 04, 2013 at 09:01:35AM -0600, Matt Domsch wrote:
> > > On Mon, Mar 04, 2013 at 08:44:55AM -0600, Domsch, Matt wrote:
> > > > The challenge here is that because struct netdev is initialized to all
> > > > zeros, code that consumes dev_id can't tell the difference between a
> > > > driver _setting_ the value to 0 because it has 2 ports 0 and 1, and a
> > > > default (unset) value of 0.  I think the only solution here is to make
> > > > sure the kernel drivers, if they need to set it, always set this
> > > > non-zero, so udev, seeing a non-zero value, knows it's a valid value
> > > > to use.
> > > 
> > > These seem to be the 4 drivers currently setting dev_id:
> > > 
> > > drivers/net/ethernet/chelsio/cxgb4/t4_hw.c:             adap->port[i]->dev_id = j;
> > > drivers/net/ethernet/freescale/fec.c:   fep->dev_id = dev_id++;
> > 
> > Look up a few lines:
> > 
> >         /* setup board info structure */
> >         fep = netdev_priv(ndev);
> > 
> > fep is not a pointer to the net_device, but to the private device
> > structure.  This is why I didn't include it in the list.
> 
> Good catch.
>  
> > > drivers/net/ethernet/mellanox/mlx4/en_netdev.c: dev->dev_id =  port - 1;
> > > drivers/net/ethernet/sfc/siena.c:       efx->net_dev->dev_id = EFX_OWORD_FIELD(reg, FRF_CZ_CS_PORT_NUM) - 1;
> > > 
> > > of these, both the mlx4 and siena drivers set them starting at 0.  I
> > > think the fec driver might be doing so as well, but it's not as
> > > obvious.  I'm pretty sure cxgb4 starts numbering at 1 just from
> > > reading the code.  So, as-is in the 3.9rc1 kernel, I wouldn't be
> > > comfortable relying on the value of dev_id.
> > 
> > I agree it looks like some cleanup is needed due to the inconsistency.
> > 
> > This is still only an issue when a single function supports multiple
> > ethernet devices, right?
> 
> I believe so, yes.
> 

Ok, good.  I did like your idea to possibly set this to something other
than 0 in the default case and then make sure that any driver that needs
to set it can do so.