netdev - Re: network status

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Message-ID: <CAM_iQpUjkWcHk+3MLiw=xSbRq0MaLKarNZoX2KBcFyTNBZsSiw@mail.gmail.com>
Date:   Wed, 25 Jan 2017 14:05:30 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Sriram V <vshrirama@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: network status

On Tue, Jan 24, 2017 at 11:39 AM, Sriram V <vshrirama@...il.com> wrote:
> Hello,
>
> Apologies in case, this is not the right list of this question.
>
> I wanted to check, How can i find out if a network status has changed
>
> 1. How can the user application find out if the link status has changed?

There are some flags per netdevice for its link status, IFF_LOWER_UP
etc., they are sent to user-space via rtnetlink message, ->ifi_flags.


> 2. what changes do i need to add in the driver to indicate to the user
> applications that ethernet cable has been plugged in or unplugged.
>

Probably nothing but calling netif_carrier_on/off() API's.


> 3. How should a user application know the status change (Should the
> userapp poll on the interface/is there an uevent interface to indicate
> the link status change)
>

It needs to subscribe to the rtnetlink group RTNLGRP_LINK to receive
the broadcasts from kernel.