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

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Message-Id: <20140603.152449.715925744030919276.davem@davemloft.net>
Date:	Tue, 03 Jun 2014 15:24:49 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	kumaran.4353@...il.com
Cc:	steve.glendinning@...well.net, netdev@...r.kernel.org
Subject: Re: [PATCH 1/1] driver: net: smsc911x: set NOCARRIER flag in
 driver initialization

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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