netdev - Re: [PATCH net-next 2/2] xen-netback: handle frontends that fail to transition through Closing

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Date:	Fri, 20 Sep 2013 14:38:46 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	Paul Durrant <paul.durrant@...rix.com>, <netdev@...r.kernel.org>,
	<xen-devel@...ts.xen.org>, Ian Campbell <ian.campbell@...rix.com>
Subject: Re: [PATCH net-next 2/2] xen-netback: handle frontends that fail
 to transition through Closing

On 20/09/13 14:34, Wei Liu wrote:
> On Fri, Sep 20, 2013 at 01:56:31PM +0100, Paul Durrant wrote:
>> Some old Windows frontends fail to transition through the xenbus Closing
>> state and move directly from Connected to Closed. Handle this case properly.
>>
>> --- a/drivers/net/xen-netback/xenbus.c
>> +++ b/drivers/net/xen-netback/xenbus.c
>> @@ -265,6 +265,8 @@ static void frontend_changed(struct xenbus_device *dev,
>>  		break;
>>  
>>  	case XenbusStateClosed:
>> +		if (dev->state == XenbusStateConnected)
>> +			disconnect_backend(dev);
> 
> Could you please add a comment above this change stating that this is a
> workaround for some old frontend that we cannot fix / upgrade.

Handling frontend CONNECTED -> CLOSED is a sensible thing for a backend
to do regardless of whether there are old frontends that do this or not.

> We would still like to later frontend goes through the normal connected
> -> closing -> closed path.

This should be documented as a full description of the two state
machines in public/io/netif.h in Xen.  Not scattered about in comments
in a particular backend implementation.

David
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