From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Fri, 30 Oct 2009 14:16:32 -0400

On Fri, Oct 30, 2009 at 11:10:27AM -0700, David Miller wrote:
. 

quoted

Because the driver must start in state with carrier off anyways,
so that we get the transition event when the device comes up
from link down to link up.

Well we want all drivers to start in state NOCARRIER.  However,
a freshly allocated netdev has the NOCARRIER bit off.  This means
every single driver has to set the NOCARRIER bit.

It would seem much easier to ensure that the NOCARRIER bit is set
in a newly allocated netdev.

Since many drivers (especially virtual software ones) do not manage
carrier state and therefore that's why we start in state carrier on.

We've had this discussion a few times before, most recently with
Rusty wrt. virtio :-)