Re: [Qemu-devel] [PATCH v2] xen: fix xen-bus state model to allow frontend re-connection

[Anthony PERARD <anthony.perard@citrix.com>]

On Tue, Jan 22, 2019 at 03:53:46PM +0000, Paul Durrant wrote:
> There is a flaw in the xen-bus state model. To allow a frontend to re-
> connect the backend state of an online XenDevice is transitioned from
> Closed to InitWait, but this is currently done unilaterally which is
> incorrect. The backend state should remain Closed until the frontend state
> transitions to Initialising.
> 
> This patch removes the automatic backend state transition from
> xen_device_backend_state_changed() and, instead, adds an extra check in
> xen_device_frontend_state_changed() to determine whether a frontend is
> trying to re-connect to a previously Closed XenDevice. Only if this is
> found to be the case is the backend state transitioned from Closed to
> InitWait. Note that this transition will be common amongst all XenDevice
> classes and hence xen_device_frontend_state_changed() returns immediately
> afterwards without calling into the XenDeviceClass frontend_changed()
> method.
> 
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>

I've tested OVMF with that patch, and states transitions looks better
when transitionning from ovmf to linux.
(Less Closed->InitWait->Closed..., and ovmf trying to win a race at
reading the backend state at the right time).

Acked-by: Anthony PERARD <anthony.perard@citrix.com>

Thanks,

-- 
Anthony PERARD