conf: give each hostdevdef a parent pointer

The parent can be any type of device. It defaults to type=none, and a
NULL pointer. The intent is that if a hostdevdef is contained in the
def for a higher level device (e.g. virDomainNetDef), hostdev->parent
will point to the higher level device, and type will be set to that
type of device. This way, during attach and detach of the device,
parent can be checked, and appropriate callouts made to do higher
level device initialization (e.g. setting MAC address).

Also, although these hostdevs with parents will be added to a domain's
hostdevs list, they will be treated slightly differently when
traversing the list, e.g. virDomainHostdefDefFree for a hostdev that
has a parent doesn't need to be called (and will be a NOP); it will
simply be removed from the list (since the parent device object is in
its own type-specific list, and will be freed from there).

src/conf/domain_conf.c

@@ -1328,7 +1328,11 @@ void virDomainHostdevDefClear(virDomainHostdevDefPtr def)
      * such resource is the virDomainDeviceInfo.
      */
 
-    virDomainDeviceInfoFree(def->info);
+    /* If there is a parent device object, it will handle freeing
+     * def->info.
+     */
+    if (def->parent.type == VIR_DOMAIN_DEVICE_NONE)
+        virDomainDeviceInfoFree(def->info);
 }
 
 void virDomainHostdevDefFree(virDomainHostdevDefPtr def)
@@ -1339,7 +1343,11 @@ void virDomainHostdevDefFree(virDomainHostdevDefPtr def)
     /* free all subordinate objects */
     virDomainHostdevDefClear(def);
 
-    VIR_FREE(def);
+    /* If there is a parent device object, it will handle freeing
+     * the memory.
+     */
+    if (def->parent.type == VIR_DOMAIN_DEVICE_NONE)
+        VIR_FREE(def);
 }
 
 void virDomainHubDefFree(virDomainHubDefPtr def)

src/conf/domain_conf.h

@@ -356,6 +356,7 @@ enum virDomainHostdevSubsysType {
 
 /* basic device for direct passthrough */
 struct _virDomainHostdevDef {
+    virDomainDeviceDef parent; /* higher level Def containing this */
     int mode; /* enum virDomainHostdevMode */
     unsigned int managed : 1;
     union {