netdev - Re: Requirements for a shutdown function?

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Date:   Tue, 9 May 2017 12:06:48 -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 05/09/2017 11:51 AM, Timur Tabi wrote:
> On 05/09/2017 01:46 PM, Florian Fainelli wrote:
>> A good test case for exercising a .shutdown() function is kexec'ing a
>> new kernel for instance.
> 
> I tried that.  I run iperf in one window while launching kexec in another.
> Even without a shutdown function, network traffic appear to halt on its own
> and the kexec succeeds.
> 
> 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.

There is no strict requirement for implementing a .shutdown() function
AFAICT and it does not necessarily make sense to have one depending on
the bus type. For platform/MMIO devices, it hardly has any value, but on
e.g: PCI, it could be added as an additional step to perform a full
device shutdown.

> 
>> You should put your HW in a state where it won't be doing DMA, or have
>> any adverse side effects to the system, putting it in a low power state
>> is also a good approach.
> 
> 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.
-- 
Florian