Xen devel - Sep 2013 - [PATCH net-next v2 2/2] xen-netback: handle frontends that fail to transition through Closing

Some old Windows frontends fail to transition through the xenbus Closing
state and move directly from Connected to Closed. Handle this case properly.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
---
 drivers/net/xen-netback/xenbus.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index a53782e..684b0f6 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -265,6 +265,13 @@ static void frontend_changed(struct xenbus_device *dev,
 		break;
 
 	case XenbusStateClosed:
+		/*
+		 * Handle frontends which erroneously transition
+		 * directly from Connected to Closed.
+		 */
+		if (dev->state == XenbusStateConnected)
+			disconnect_backend(dev);
+
 		xenbus_switch_state(dev, XenbusStateClosed);
 		if (xenbus_dev_is_online(dev))
 			break;
-- 
1.7.10.4

On Fri, Sep 20, 2013 at 02:57:40PM +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.
What happens in this case? Are there other state changes that will do
unwanted things?

Bastian

-- 
If there are self-made purgatories, then we all have to live in them.
		-- Spock, "This Side of Paradise", stardate 3417.7

> -----Original Message-----
> From: Bastian Blank [mailto:bastian@waldi.eu.org]
> Sent: 20 September 2013 17:15
> To: Paul Durrant
> Cc: netdev@vger.kernel.org; xen-devel@lists.xen.org; Wei Liu; David Vrabel;
> Ian Campbell
> Subject: Re: [Xen-devel] [PATCH net-next v2 2/2] xen-netback: handle
> frontends that fail to transition through Closing
> 
> On Fri, Sep 20, 2013 at 02:57:40PM +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.
> 
> What happens in this case? Are there other state changes that will do
> unwanted things?
> 
Hmm, now you mention it I suspect a transition directly to an unknown state may
also not do the right thing. Perhaps it would be better to go straight to a more
robust state model as suggested by David Vrabel.

  Paul