hw/xen: do not repeatedly try to create a failing backend device

If xen_backend_device_create() fails to instantiate a device, the XenBus
code will just keep trying over and over again each time the bus is
re-enumerated, as long as the backend appears online and in
XenbusStateInitialising.

The only thing which prevents the XenBus code from recreating duplicates
of devices which already exist, is the fact that xen_device_realize()
sets the backend state to XenbusStateInitWait. If the attempt to create
the device doesn't get *that* far, that's when it will keep getting
retried.

My first thought was to handle errors by setting the backend state to
XenbusStateClosed, but that doesn't work for XenConsole which wants to
*ignore* any device of type != "ioemu" completely.

So, make xen_backend_device_create() *keep* the XenBackendInstance for a
failed device, and provide a new xen_backend_exists() function to allow
xen_bus_type_enumerate() to check whether one already exists before
creating a new one.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index 12ff782005..3ffd1a5333 100644
--- a/hw/xen/xen-bus.c
+++ b/hw/xen/xen-bus.c
@@ -209,7 +209,8 @@ static void xen_bus_type_enumerate(XenBus *xenbus, const char *type)
                           NULL, "%u", &online) != 1)
             online = 0;
 
-        if (online && state == XenbusStateInitialising) {
+        if (online && state == XenbusStateInitialising &&
+            !xen_backend_exists(type, backend[i])) {
             Error *local_err = NULL;
 
             xen_bus_backend_create(xenbus, type, backend[i], backend_path,