rbd-mirror: Add sparse read for sync image

Currently, the image sync do full read, and we shall add sparse read
to let the sync more efficiently.

Feature: http://tracker.ceph.com/issues/16780
Signed-off-by: tianqing <tianqing@unitedstack.com>

src/tools/rbd_mirror/image_sync/ObjectCopyRequest.cc

@@ -103,6 +103,8 @@ void ObjectCopyRequest<I>::send_read_object() {
 
   bool read_required = false;
   librados::ObjectReadOperation op;
+  std::map<uint64_t, uint64_t> extents;
+  bufferlist xbl;
   for (auto &sync_op : sync_ops) {
     switch (std::get<0>(sync_op)) {
     case SYNC_OP_TYPE_WRITE:
@@ -113,8 +115,15 @@ void ObjectCopyRequest<I>::send_read_object() {
 
       dout(20) << ": read op: " << std::get<1>(sync_op) << "~"
                << std::get<2>(sync_op) << dendl;
-      op.read(std::get<1>(sync_op), std::get<2>(sync_op),
-              &std::get<3>(sync_op), nullptr);
+      op.sparse_read(std::get<1>(sync_op), std::get<2>(sync_op), &extents,
+                     &xbl, nullptr);
+      for(auto& kv : extents){
+        // print the extents
+        dout(20) << "extents: ["<< kv.first << ", " << kv.second << "]" << dendl;
+      }
+      // put it into bl
+      ::encode(extents, std::get<3>(sync_op));
+      ::encode(xbl, std::get<3>(sync_op));
       break;
     default:
       break;
@@ -175,12 +184,26 @@ void ObjectCopyRequest<I>::send_write_object() {
   assert(!sync_ops.empty());
 
   librados::ObjectWriteOperation op;
+  bufferlist::iterator it;
+  std::map<uint64_t, uint64_t> extents;
+  bufferlist databl;
+  uint64_t len = 0;
+  uint64_t begin = 0;
   for (auto &sync_op : sync_ops) {
     switch (std::get<0>(sync_op)) {
     case SYNC_OP_TYPE_WRITE:
+      it = std::get<3>(sync_op).begin();
+      ::decode(extents, it);
+      ::decode(databl, it);
+      for(auto &it : extents){
+         bufferlist tmpbl;
+         len = it.second - it.first;
+         tmpbl.copy_in(begin, len, databl);
+         op.writesame(it.first, it.second, tmpbl);
+         begin += len;
+      }
       dout(20) << ": write op: " << std::get<1>(sync_op) << "~"
-               << std::get<3>(sync_op).length() << dendl;
-      op.write(std::get<1>(sync_op), std::get<3>(sync_op));
+               << databl.length() << dendl;
       break;
     case SYNC_OP_TYPE_TRUNC:
       dout(20) << ": trunc op: " << std::get<1>(sync_op) << dendl;