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

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Message-ID: <9AAE0902D5BC7E449B7C8E4E778ABCD010EFF2@AMSPEX01CL01.citrite.net>
Date:	Fri, 20 Sep 2013 13:40:59 +0000
From:	Paul Durrant <Paul.Durrant@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xen.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

> -----Original Message-----
> From: David Vrabel
> Sent: 20 September 2013 14:39
> To: Wei Liu
> Cc: Paul Durrant; netdev@...r.kernel.org; xen-devel@...ts.xen.org; Ian
> Campbell
> 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.
> 

Agreed, but probably still worth the comment in case someone gets the wrong idea.

  Paul

> > 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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