netdev - Re: Requirements for a shutdown function?

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Message-ID: <358a4a6f-5c47-dae8-38bf-67150cba1b07@gmail.com>
Date:   Wed, 10 May 2017 14:47:23 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Timur Tabi <timur@...eaurora.org>, netdev@...r.kernel.org
Subject: Re: Requirements for a shutdown function?

On 05/10/2017 01:17 PM, Timur Tabi wrote:
> On 05/09/2017 02:06 PM, Florian Fainelli wrote:
>> On 05/09/2017 11:51 AM, Timur Tabi wrote:
> 
>>> Is it possible that the network stack detects a kexec and automatically
>>> stops all network devices?
>>
>> No. why would it? However the device driver model does call into your
>> driver's remove function and that one does a right job already because
>> it does an network device unregister, and so on.
> 
> I ran some more tests.  When I launch kexec, the driver's
> net_device_ops.ndo_stop function is called, which already stops the interface.
> 
> So it looks to me as if the network stack does close the interface during a
> kexec.  With the interface closed, there's no point in having a shutdown
> function, is there?

AFAIR kexec takes care of shutting down network devices explicitly
(unless instructed otherwise with -x/--no-ifdown) so this may be where
this is coming from.

Reading through drivers/base/core.c it does not appear that ->remove()
is called and then ->shutdown() gets called, only ->shutdown() gets
called from device_shutdown() called from kernel/reboot.c. It seems to
me like if you want to be on the safe side you would want to implement a
shutdown function that is identical to what your remove function does.

> 
>>> My in-house driver stops the RX and TX queues.  I'm guessing that's good
>>> enough, but I don't have a failing test case to prove it.
>>>
>>
>> That's probably good enough, yes.
> 
> Except that it turns out that the queues are already stopped by then because
> the emac_close() function has already been called.

-- 
Florian