node device driver: update driver name during dumpxml

This fixes:

  https://bugzilla.redhat.com/show_bug.cgi?id=979290
  https://bugzilla.redhat.com/show_bug.cgi?id=979330

The node device driver was written with the assumption that udev would
use a "change" event to notify libvirt of any change to device status
(including the name of the driver it was bound to). It turns out this
is not the case (see Comment 4 of BZ 979290). That means that a
dumpxml for a device would always show whatever driver happened to be
bound at the time libvirt was started (when the node device cache was
built).

There was already code in the driver (for the benefit of the HAL
backend) that updated the driver name from sysfs each time a device's
info was retrieved from the cache. This patch just enables that manual
update for the udev backend as well.

diff --git a/src/node_device/node_device_driver.c b/src/node_device/node_device_driver.c
index 67e90a1207be94f0dbdef7444a9322532d93362a..8e6911acdb5ac088bda8c0747995570e80966982 100644 (file)
--- a/src/node_device/node_device_driver.c
+++ b/src/node_device/node_device_driver.c
@@ -60,10 +60,15 @@ static int update_caps(virNodeDeviceObjPtr dev)
 }
 
 
-#if defined (__linux__) && defined (WITH_HAL)
-/* Under libudev changes to the driver name should be picked up as
- * "change" events, so we don't call update driver name unless we're
- * using the HAL backend. */
+#if defined (__linux__) && ( defined (WITH_HAL) || defined(WITH_UDEV))
+/* NB: It was previously believed that changes in driver name were
+ * relayed to libvirt as "change" events by udev, and the udev event
+ * notification is setup to recognize such events and effectively
+ * recreate the device entry in the cache. However, neither the kernel
+ * nor udev sends such an event, so it is necessary to manually update
+ * the driver name for a device each time its entry is used, both for
+ * udev *and* HAL backends.
+ */
 static int update_driver_name(virNodeDeviceObjPtr dev)
 {
     char *driver_link = NULL;