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xen-bus: Fix backend state transition on device reset 

When a frontend wants to reset its state and the backend one, it
starts with setting "Closing", then waits for the backend (QEMU) to do
the same.

But when QEMU is setting "Closing" to its state, it triggers an event
(xenstore watch) that re-execute xen_device_backend_changed() and set
the backend state to "Closed". QEMU should wait for the frontend to
set "Closed" before doing the same.

Before setting "Closed" to the backend_state, we are also going to
check if there is a frontend. If that the case, when the backend state
is set to "Closing" the frontend should react and sets its state to
"Closing" then "Closed". The backend should wait for that to happen.

Fixes: b6af8926fb
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Message-Id: <20190823101534.465-2-anthony.perard@citrix.com>
stable-4.2
Anthony PERARD 2019-08-23 11:15:33 +01:00
parent ba7fdd64b6
commit cb32314607
1 changed files with 20 additions and 3 deletions
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23
hw/xen/xen-bus.c
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@ -516,6 +516,23 @@ static void xen_device_backend_set_online(XenDevice *xendev, bool online)
xen_device_backend_printf(xendev, "online", "%u", online);
}
/*
* Tell from the state whether the frontend is likely alive,
* i.e. it will react to a change of state of the backend.
*/
static bool xen_device_state_is_active(enum xenbus_state state)
{
switch (state) {
case XenbusStateInitWait:
case XenbusStateInitialised:
case XenbusStateConnected:
case XenbusStateClosing:
return true;
default:
return false;
}
}
static void xen_device_backend_changed(void *opaque)
{
XenDevice *xendev = opaque;
@ -539,11 +556,11 @@ static void xen_device_backend_changed(void *opaque)
/*
* If the toolstack (or unplug request callback) has set the backend
* state to Closing, but there is no active frontend (i.e. the
* state is not Connected) then set the backend state to Closed.
* state to Closing, but there is no active frontend then set the
* backend state to Closed.
*/
if (xendev->backend_state == XenbusStateClosing &&
xendev->frontend_state != XenbusStateConnected) {
!xen_device_state_is_active(state)) {
xen_device_backend_set_state(xendev, XenbusStateClosed);
}