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Re: [Qemu-devel] [PATCH] xen: fix xen-bus state model to allow frontend
From: |
Paul Durrant |
Subject: |
Re: [Qemu-devel] [PATCH] xen: fix xen-bus state model to allow frontend re-connection |
Date: |
Tue, 22 Jan 2019 15:38:26 +0000 |
> -----Original Message-----
> From: Paul Durrant [mailto:address@hidden
> Sent: 22 January 2019 14:40
> To: address@hidden; address@hidden
> Cc: Paul Durrant <address@hidden>; Stefano Stabellini
> <address@hidden>; Anthony Perard <address@hidden>
> Subject: [PATCH] xen: fix xen-bus state model to allow frontend re-
> connection
>
> 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 <address@hidden>
Unfortunately this is still not quite right. Further testing has now shown that
xl block-detach is no longer working properly. I'll send a v2 once that is
fixed.
Paul
> ---
> Cc: Stefano Stabellini <address@hidden>
> Cc: Anthony Perard <address@hidden>
> ---
> hw/xen/xen-bus.c | 27 +++++++++++++++------------
> 1 file changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
> index 3aeccec69c..1b31a1dc50 100644
> --- a/hw/xen/xen-bus.c
> +++ b/hw/xen/xen-bus.c
> @@ -547,20 +547,12 @@ static void xen_device_backend_changed(void *opaque)
> }
>
> /*
> - * If a backend is still 'online' then its state should be cycled
> - * back round to InitWait in order for a new frontend instance to
> - * connect. This may happen when, for example, a frontend driver is
> - * re-installed or updated.
> - * If a backend is not 'online' then the device should be destroyed.
> + * If a backend is still 'online' then we should leave it alone but,
> + * if a backend is not 'online', then the device should be destroyed
> + * once the state is Closed.
> */
> - if (xendev->backend_online &&
> + if (!xendev->backend_online &&
> xendev->backend_state == XenbusStateClosed) {
> - xen_device_backend_set_state(xendev, XenbusStateInitWait);
> - } else if (!xendev->backend_online &&
> - (xendev->backend_state == XenbusStateClosed ||
> - xendev->backend_state == XenbusStateInitialising ||
> - xendev->backend_state == XenbusStateInitWait ||
> - xendev->backend_state == XenbusStateUnknown)) {
> Error *local_err = NULL;
>
> if (!xen_backend_try_device_destroy(xendev, &local_err)) {
> @@ -715,6 +707,17 @@ static void xen_device_frontend_changed(void *opaque)
>
> xen_device_frontend_set_state(xendev, state);
>
> + if (state == XenbusStateInitialising &&
> + xendev->backend_state == XenbusStateClosed &&
> + xendev->backend_online) {
> + /*
> + * The frontend is re-initializing so switch back to
> + * InitWait.
> + */
> + xen_device_backend_set_state(xendev, XenbusStateInitWait);
> + return;
> + }
> +
> if (xendev_class->frontend_changed) {
> Error *local_err = NULL;
>
> --
> 2.20.1.2.gb21ebb6