memory: introduce memory_region_test_and_clear_dirty

This function avoids having to do two calls, one to test the dirty bit, and
other to reset it.
Signed-off-by: Juan Quintela <quintela@redhat.com>

include/exec/memory.h

@@ -453,6 +453,22 @@ bool memory_region_get_dirty(MemoryRegion *mr, hwaddr addr,
 void memory_region_set_dirty(MemoryRegion *mr, hwaddr addr,
                              hwaddr size);
 
+/**
+ * memory_region_test_and_clear_dirty: Check whether a range of bytes is dirty
+ *                                     for a specified client. It clears them.
+ *
+ * Checks whether a range of bytes has been written to since the last
+ * call to memory_region_reset_dirty() with the same @client.  Dirty logging
+ * must be enabled.
+ *
+ * @mr: the memory region being queried.
+ * @addr: the address (relative to the start of the region) being queried.
+ * @size: the size of the range being queried.
+ * @client: the user of the logging information; %DIRTY_MEMORY_MIGRATION or
+ *          %DIRTY_MEMORY_VGA.
+ */
+bool memory_region_test_and_clear_dirty(MemoryRegion *mr, hwaddr addr,
+                                        hwaddr size, unsigned client);
 /**
  * memory_region_sync_dirty_bitmap: Synchronize a region's dirty bitmap with
  *                                  any external TLBs (e.g. kvm)

memory.c

@@ -1081,6 +1081,22 @@ void memory_region_set_dirty(MemoryRegion *mr, hwaddr addr,
     return cpu_physical_memory_set_dirty_range(mr->ram_addr + addr, size, -1);
 }
 
+bool memory_region_test_and_clear_dirty(MemoryRegion *mr, hwaddr addr,
+                                        hwaddr size, unsigned client)
+{
+    bool ret;
+    assert(mr->terminates);
+    ret = cpu_physical_memory_get_dirty(mr->ram_addr + addr, size,
+                                        1 << client);
+    if (ret) {
+        cpu_physical_memory_reset_dirty(mr->ram_addr + addr,
+                                        mr->ram_addr + addr + size,
+                                        1 << client);
+    }
+    return ret;
+}
+
+
 void memory_region_sync_dirty_bitmap(MemoryRegion *mr)
 {
     AddressSpace *as;