[PATCH RFC 3/9] memory: Introduce log_sync_global() to memory listener

[Peter Xu <peterx@redhat.com>]

Some of the memory listener may want to do log synchronization without
being able to specify a range of memory to sync but always globally.
Such a memory listener should provide this new method instead of the
log_sync() method.

Obviously we can also achieve similar thing when we put the global
sync logic into a log_sync() handler. However that's not efficient
enough because otherwise memory_global_dirty_log_sync() may do the
global sync N times, where N is the number of flat views.

Make this new method be exclusive to log_sync().

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 include/exec/memory.h | 12 ++++++++++++
 memory.c              | 33 +++++++++++++++++++++++----------
 2 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index e85b7de99a..c4427094bb 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -533,6 +533,18 @@ struct MemoryListener {
      */
     void (*log_sync)(MemoryListener *listener, MemoryRegionSection *section);
 
+    /**
+     * @log_sync_global:
+     *
+     * This is the global version of @log_sync when the listener does
+     * not have a way to synchronize the log with finer granularity.
+     * When the listener registers with @log_sync_global defined, then
+     * its @log_sync must be NULL.  Vice versa.
+     *
+     * @listener: The #MemoryListener.
+     */
+    void (*log_sync_global)(MemoryListener *listener);
+
     /**
      * @log_clear:
      *
diff --git a/memory.c b/memory.c
index aeaa8dcc9e..53828ba00c 100644
--- a/memory.c
+++ b/memory.c
@@ -2016,6 +2016,10 @@ void memory_region_set_dirty(MemoryRegion *mr, hwaddr addr,
                                         memory_region_get_dirty_log_mask(mr));
 }
 
+/*
+ * If memory region `mr' is NULL, do global sync.  Otherwise, sync
+ * dirty bitmap for the specified memory region.
+ */
 static void memory_region_sync_dirty_bitmap(MemoryRegion *mr)
 {
     MemoryListener *listener;
@@ -2029,18 +2033,24 @@ static void memory_region_sync_dirty_bitmap(MemoryRegion *mr)
      * address space once.
      */
     QTAILQ_FOREACH(listener, &memory_listeners, link) {
-        if (!listener->log_sync) {
-            continue;
-        }
-        as = listener->address_space;
-        view = address_space_get_flatview(as);
-        FOR_EACH_FLAT_RANGE(fr, view) {
-            if (fr->dirty_log_mask && (!mr || fr->mr == mr)) {
-                MemoryRegionSection mrs = section_from_flat_range(fr, view);
-                listener->log_sync(listener, &mrs);
+        if (listener->log_sync) {
+            as = listener->address_space;
+            view = address_space_get_flatview(as);
+            FOR_EACH_FLAT_RANGE(fr, view) {
+                if (fr->dirty_log_mask && (!mr || fr->mr == mr)) {
+                    MemoryRegionSection mrs = section_from_flat_range(fr, view);
+                    listener->log_sync(listener, &mrs);
+                }
             }
+            flatview_unref(view);
+        } else if (listener->log_sync_global) {
+            /*
+             * No matter whether MR is specified, what we can do here
+             * is to do a global sync, because we are not capable to
+             * sync in a finer granularity.
+             */
+            listener->log_sync_global(listener);
         }
-        flatview_unref(view);
     }
 }
 
@@ -2727,6 +2737,9 @@ void memory_listener_register(MemoryListener *listener, AddressSpace *as)
 {
     MemoryListener *other = NULL;
 
+    /* Only one of them can be defined for a listener */
+    assert(!(listener->log_sync && listener->log_sync_global));
+
     listener->address_space = as;
     if (QTAILQ_EMPTY(&memory_listeners)
         || listener->priority >= QTAILQ_LAST(&memory_listeners)->priority) {
-- 
2.24.1