netdev - Re: [PATCH 1/1] driver: net: smsc911x: set NOCARRIER flag in driver initialization

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Message-ID: <CAHPKR9LUOLQgVR6Sz_LB+3ggLCeRPf95cQEs7aP94LAOwfz5gw@mail.gmail.com>
Date:	Wed, 4 Jun 2014 10:35:50 +0530
From:	Balakumaran Kannan <kumaran.4353@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Steve Glendinning <steve.glendinning@...well.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/1] driver: net: smsc911x: set NOCARRIER flag in driver initialization

Thank you very much Florian and David for great explanation.

Regards,
K.Balakumaran

On Wed, Jun 4, 2014 at 3:54 AM, David Miller <davem@...emloft.net> wrote:
> From: Balakumaran Kannan <kumaran.4353@...il.com>
> Date: Tue, 3 Jun 2014 19:45:39 +0530
>
>> On Sat, May 31, 2014 at 2:12 AM, David Miller <davem@...emloft.net> wrote:
>>> From: Balakumaran Kannan <kumaran.4353@...il.com>
>>> Date: Fri, 30 May 2014 18:35:43 +0530
>>>
>>>> All these drivers call netif_carrier_off function after registering
>>>> the network device using register_netdev.
>>>
>>> I can quote more counter-examples than your list, starting with the
>>> Broadcom tg3 driver.
>>
>> Thank you David for this information. I'll send updated patch as version-2.
>>
>> Still I couldn't understand the reason behind this. I should be grateful if you
>> would explain me little bit.
>
> At the moment you call register_netdev() the device is visible, notifications
> are sent to userspace, and userland tools can try to bring the interface up
> and see the incorrect link state, before you do the netif_carrier_off().
>
> Said another way, between the register_netdev() and netif_carrier_off() call,
> userspace can see the device in an inconsistent state.
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