Re: [dpdk-dev] [PATCH v2 10/10] kni: add API to set link status on kernel interface

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 29 Aug 2018 18:10:35 -0300
Dan Gora <dg@adax.com> wrote:

> On Wed, Aug 29, 2018 at 8:48 AM, Ferruh Yigit <ferruh.yigit@intel.com> wrote:
> > On 6/29/2018 2:55 AM, Dan Gora wrote:  
> >> Add a new API function to KNI, rte_kni_update_link() to allow DPDK
> >> applications to update the link state for the KNI network interfaces
> >> in the linux kernel.
> >>
> >> Note that the default carrier state is set to off when the interface
> >> is opened.  
> >
> > Why set carrier off when interface opened?  
> 
> A couple of reasons:
> 
> 1) That's the way every other Ethernet driver in the linux kernel does
> it that I've seen.
> 
> 2) The DPDK application may not actually be ready for the interface to
> be used when it is first created.  Things like NetworkManager, etc
> will gladly go trying to assign IP addresses to those interfaces, add
> them to the routing table, etc as soon as the interface is marked
> "up".  By making the default be "down", this allows the application to
> finish any initialization on the DPDK side of the interface before
> allowing it to be used by the kernel.
> 
> > Although I don't see any difference
> > in interface state with or without this call.  
> 
> Previously in the 'ip addr' output, the 'state' would be 'UNKNOWN'
> when the interface was created.  After this patch the 'state' in 'ip
> addr' is 'DOWN'.
> 
> thanks
> dan

There is also a better (richer) API for link status on linux via
the operstate functions. Those might better match the semantics of
a tunnellish interface like KNI.