librbd: only send non-zero copyup data

If the parent image is logically zero for the range of a child object,
it's equivalent to the object not existing. Save some I/O and network
bandwidth and don't send the useless zeroes.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>

diff --git a/src/librbd/AioRequest.cc b/src/librbd/AioRequest.cc
index 8d4d98c0bd0f150194d551e050be1dfd51ac552a..83e19272f8d2fbc44d8aa7f0caa10b5aaa5176be 100644 (file)
--- a/src/librbd/AioRequest.cc
+++ b/src/librbd/AioRequest.cc
@@ -234,7 +234,8 @@ namespace librbd {
   }
 
   void AbstractWrite::send_copyup() {
-    m_copyup.exec("rbd", "copyup", m_read_data);
+    if (!m_read_data.is_zero())
+      m_copyup.exec("rbd", "copyup", m_read_data);
     add_copyup_ops();
 
     librados::AioCompletion *rados_completion =