memory: support stateless memory listeners

Current memory listeners are incremental; that is, they are expected to
maintain their own state, and receive callbacks for changes to that state.

This patch adds support for stateless listeners; these work by receiving
a ->begin() callback (which tells them that new state is coming), a
sequence of ->region_add() and ->region_nop() callbacks, and then a
->commit() callback which signifies the end of the new state.  They should
ignore ->region_del() callbacks.

Signed-off-by: Avi Kivity <avi@redhat.com>

kvm-all.c

@@ -680,6 +680,14 @@ static void kvm_set_phys_mem(MemoryRegionSection *section, bool add)
     }
 }
 
+static void kvm_begin(MemoryListener *listener)
+{
+}
+
+static void kvm_commit(MemoryListener *listener)
+{
+}
+
 static void kvm_region_add(MemoryListener *listener,
                            MemoryRegionSection *section)
 {
@@ -692,6 +700,11 @@ static void kvm_region_del(MemoryListener *listener,
     kvm_set_phys_mem(section, false);
 }
 
+static void kvm_region_nop(MemoryListener *listener,
+                           MemoryRegionSection *section)
+{
+}
+
 static void kvm_log_sync(MemoryListener *listener,
                          MemoryRegionSection *section)
 {
@@ -795,8 +808,11 @@ static void kvm_eventfd_del(MemoryListener *listener,
 }
 
 static MemoryListener kvm_memory_listener = {
+    .begin = kvm_begin,
+    .commit = kvm_commit,
     .region_add = kvm_region_add,
     .region_del = kvm_region_del,
+    .region_nop = kvm_region_nop,
     .log_start = kvm_log_start,
     .log_stop = kvm_log_stop,
     .log_sync = kvm_log_sync,