diff mbox series

[PULL,4/4] xen-bus: Avoid rewriting identical values to xenstore

Message ID 20190827133259.32084-5-anthony.perard@citrix.com
State New
Headers show
Series [PULL,1/4] xen: Fix ring.h header | expand

Commit Message

Anthony PERARD Aug. 27, 2019, 1:32 p.m. UTC 
When QEMU receives a xenstore watch event suggesting that the "state"
of the frontend changed, it records this in its own state but it also
re-write the value back into xenstore even so there were no change.
This triggers an unnecessary xenstore watch event which QEMU will
process again (and maybe the frontend as well). Also QEMU could
potentially write an already old value.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Message-Id: <20190823101534.465-3-anthony.perard@citrix.com>
---
 hw/xen/xen-bus.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)
diff mbox series

Patch

diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index 62c127b926..a04478ad4f 100644
--- a/hw/xen/xen-bus.c
+++ b/hw/xen/xen-bus.c
@@ -698,7 +698,8 @@  int xen_device_frontend_scanf(XenDevice *xendev, const char *key,
 }
 
 static void xen_device_frontend_set_state(XenDevice *xendev,
-                                          enum xenbus_state state)
+                                          enum xenbus_state state,
+                                          bool publish)
 {
     const char *type = object_get_typename(OBJECT(xendev));
 
@@ -710,7 +711,9 @@  static void xen_device_frontend_set_state(XenDevice *xendev,
                                     xs_strstate(state));
 
     xendev->frontend_state = state;
-    xen_device_frontend_printf(xendev, "state", "%u", state);
+    if (publish) {
+        xen_device_frontend_printf(xendev, "state", "%u", state);
+    }
 }
 
 static void xen_device_frontend_changed(void *opaque)
@@ -726,7 +729,7 @@  static void xen_device_frontend_changed(void *opaque)
         state = XenbusStateUnknown;
     }
 
-    xen_device_frontend_set_state(xendev, state);
+    xen_device_frontend_set_state(xendev, state, false);
 
     if (state == XenbusStateInitialising &&
         xendev->backend_state == XenbusStateClosed &&
@@ -1169,7 +1172,7 @@  static void xen_device_realize(DeviceState *dev, Error **errp)
     xen_device_frontend_printf(xendev, "backend-id", "%u",
                                xenbus->backend_id);
 
-    xen_device_frontend_set_state(xendev, XenbusStateInitialising);
+    xen_device_frontend_set_state(xendev, XenbusStateInitialising, true);
 
     xendev->exit.notify = xen_device_exit;
     qemu_add_exit_notifier(&xendev->exit);