linux-kernel - Re: [PATCH] xen/pci: Deal with toolstack missing an 'XenbusStateClosing'.

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Message-ID: <51B743EA.5020800@eu.citrix.com>
Date:	Tue, 11 Jun 2013 16:36:10 +0100
From:	George Dunlap <george.dunlap@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	<xen-devel@...ts.xensource.com>, <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	<linux-pci@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH] xen/pci: Deal with toolstack missing an 'XenbusStateClosing'.

On 06/10/2013 10:06 PM, Konrad Rzeszutek Wilk wrote:
> There are two tool-stack that can instruct the Xen PCI frontend
> and backend to change states: 'xm' (Python code with a daemon),
> and 'xl' (C library - does not keep state changes).
>
> With the 'xm', the path to disconnect a PCI device (xm pci-detach
> <guest> <BDF>)is:
>
> 4(Connected)->7(Reconfiguring*)-> 8(Reconfigured)-> 4(Connected)->5(Closing*).
>
> The * is for states that the tool-stack sets. For 'xl', it is similar:
>
> 4(Connected)->7(Reconfiguring*)-> 8(Reconfigured)-> 4(Connected)
>
> Both of them also tear down the XenBus structure, so the backend
> state ends up going in the 3(Initialised) and calls pcifront_xenbus_remove.

So I looked a little bit into this; there are actually two different 
states that happen as part of this handshake.  In order to disonnect a 
*device*, xl signals using the *bus* state, like this:
* Wait for the *bus* to be in state 4(Connected)
* Set the *device* state to 5(Closing)
* Set the *bus* state to 7(Reconfiguring)
* Wait for the *bus* state to return to 4(Connected)

So are all of these states you see the *bus* state?  And why would you 
disconnect the whole pci bus if you're only removing one device?

  -George
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