Re: [Xen-devel] [Xen-unstable] XenbusState signaling with regard to pci-detach on HVM guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.08.14 at 00:04, <linux@xxxxxxxxxxxxxx> wrote:
> Here are both a crude patch for xen/libxl and pciback that change the 
> signaling 
> and now allow the removal of an individual pci device from a HVM guest.
> I hope i took the right states based on the descriptions and code i found.
> 
> What these patches try to do on remove of a pci device (and when everything 
> goes well) is:
> - after libxl has removed the device from the guest with a qmp command
> - let libxl set the pci-device-state to XenbusStateClosing AND 
>   set pci-root-state to XenbusStateReconfiguring
> - libxl waits for the pci-root-state to change to XenbusStateReconfigured
> 
> - pciback has a watch on the pci-root-state and removes the device and resets 
> in 
>   pci config space, after that it sets the pci-device-state to 
> XenbusStateClosed AND
>   set pci-root-state to XenbusStateReconfigured
> 
> - libxl now continues from the on XenbusStateReconfigured, cleans up the 
> xenstore entries for 
>   the device and finally sets pci-root-state back to XenbusStateConnected

A fundamental question: Will the changed libxl work with an
unchanged pciback no worse than the unchanged libxl does in
all possible scenarios? The thing is that extending the required
protocol between two components may only be done in a fully
backward compatible way.

Jan


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