xen-bus: reduce scope of backend watch

Currently a single watch on /local/domain/X/backend is registered by each
QEMU process running in service domain X (where X is usually 0). The purpose
of this watch is to ensure that QEMU is notified when the Xen toolstack
creates a new device backend area.
Such a backend area is specific to a single frontend area created for a
specific guest domain and, since each QEMU process is also created to service
a specfic guest domain, it is unnecessary and inefficient to notify all QEMU
processes.
Only the QEMU process associated with the same guest domain need
receive the notification. This patch re-factors the watch registration code
such that notifications are targetted appropriately.

Reported-by: Jerome Leseinne <jerome.leseinne@gmail.com>
Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20201001081500.1026-1-paul@xen.org>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/hw/xen/xen-backend.h b/include/hw/xen/xen-backend.h
index 010d712638..aac2fd454d 100644
--- a/include/hw/xen/xen-backend.h
+++ b/include/hw/xen/xen-backend.h
@@ -31,6 +31,7 @@ void xen_backend_set_device(XenBackendInstance *backend,
 XenDevice *xen_backend_get_device(XenBackendInstance *backend);
 
 void xen_backend_register(const XenBackendInfo *info);
+const char **xen_backend_get_types(unsigned int *nr);
 
 void xen_backend_device_create(XenBus *xenbus, const char *type,
                                const char *name, QDict *opts, Error **errp);