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

[Dan Gora <dg@adax.com>]

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