diff --git a/payload_consumer/delta_performer_unittest.cc b/payload_consumer/delta_performer_unittest.cc
index 2f308c0..74f17d2 100644
--- a/payload_consumer/delta_performer_unittest.cc
+++ b/payload_consumer/delta_performer_unittest.cc
@@ -228,13 +228,13 @@
     new_part.path = "/dev/zero";
     new_part.size = 1234;
 
-    payload.AddPartition(*old_part, new_part, aops, {});
+    payload.AddPartition(*old_part, new_part, aops, {}, 0);
 
     // We include a kernel partition without operations.
     old_part->name = kPartitionNameKernel;
     new_part.name = kPartitionNameKernel;
     new_part.size = 0;
-    payload.AddPartition(*old_part, new_part, {}, {});
+    payload.AddPartition(*old_part, new_part, {}, {}, 0);
 
     ScopedTempFile payload_file("Payload-XXXXXX");
     string private_key =
diff --git a/payload_consumer/vabc_partition_writer.cc b/payload_consumer/vabc_partition_writer.cc
index 9e4d9b8..73bf413 100644
--- a/payload_consumer/vabc_partition_writer.cc
+++ b/payload_consumer/vabc_partition_writer.cc
@@ -24,6 +24,7 @@
 #include "update_engine/common/cow_operation_convert.h"
 #include "update_engine/common/utils.h"
 #include "update_engine/payload_consumer/extent_writer.h"
+#include "update_engine/payload_consumer/file_descriptor.h"
 #include "update_engine/payload_consumer/install_plan.h"
 #include "update_engine/payload_consumer/partition_writer.h"
 #include "update_engine/payload_consumer/snapshot_extent_writer.h"
@@ -90,35 +91,44 @@
   // TODO(zhangkelvin) Rewrite this in C++20 coroutine once that's available.
   auto converted = ConvertToCowOperations(partition_update_.operations(),
                                           partition_update_.merge_operations());
-  std::vector<uint8_t> buffer(block_size_);
+
+  WriteAllCowOps(block_size_, converted, cow_writer_.get(), source_fd_);
+  // Emit label 0 to mark end of all SOURCE_COPY operations
+  cow_writer_->AddLabel(0);
+  TEST_AND_RETURN_FALSE(
+      prefs_->SetInt64(kPrefsUpdateStatePartitionNextOperation, 0));
+  return true;
+}
+
+bool VABCPartitionWriter::WriteAllCowOps(
+    size_t block_size,
+    const std::vector<CowOperation>& converted,
+    android::snapshot::ICowWriter* cow_writer,
+    FileDescriptorPtr source_fd) {
+  std::vector<uint8_t> buffer(block_size);
 
   for (const auto& cow_op : converted) {
     switch (cow_op.op) {
       case CowOperation::CowCopy:
         TEST_AND_RETURN_FALSE(
-            cow_writer_->AddCopy(cow_op.dst_block, cow_op.src_block));
+            cow_writer->AddCopy(cow_op.dst_block, cow_op.src_block));
         break;
       case CowOperation::CowReplace:
         ssize_t bytes_read = 0;
-        TEST_AND_RETURN_FALSE(utils::PReadAll(source_fd_,
+        TEST_AND_RETURN_FALSE(utils::PReadAll(source_fd,
                                               buffer.data(),
-                                              block_size_,
-                                              cow_op.src_block * block_size_,
+                                              block_size,
+                                              cow_op.src_block * block_size,
                                               &bytes_read));
-        if (bytes_read <= 0 || static_cast<size_t>(bytes_read) != block_size_) {
+        if (bytes_read <= 0 || static_cast<size_t>(bytes_read) != block_size) {
           LOG(ERROR) << "source_fd->Read failed: " << bytes_read;
           return false;
         }
-        TEST_AND_RETURN_FALSE(cow_writer_->AddRawBlocks(
-            cow_op.dst_block, buffer.data(), block_size_));
+        TEST_AND_RETURN_FALSE(cow_writer->AddRawBlocks(
+            cow_op.dst_block, buffer.data(), block_size));
         break;
     }
   }
-
-  // Emit label 0 to mark end of all SOURCE_COPY operations
-  cow_writer_->AddLabel(0);
-  TEST_AND_RETURN_FALSE(
-      prefs_->SetInt64(kPrefsUpdateStatePartitionNextOperation, 0));
   return true;
 }
 
diff --git a/payload_consumer/vabc_partition_writer.h b/payload_consumer/vabc_partition_writer.h
index 3fc97ce..ddade70 100644
--- a/payload_consumer/vabc_partition_writer.h
+++ b/payload_consumer/vabc_partition_writer.h
@@ -18,9 +18,11 @@
 #define UPDATE_ENGINE_VABC_PARTITION_WRITER_H_
 
 #include <memory>
+#include <vector>
 
 #include <libsnapshot/snapshot_writer.h>
 
+#include "update_engine/common/cow_operation_convert.h"
 #include "update_engine/payload_consumer/install_plan.h"
 #include "update_engine/payload_consumer/partition_writer.h"
 
@@ -44,6 +46,11 @@
   [[nodiscard]] bool Flush() override;
   void CheckpointUpdateProgress(size_t next_op_index) override;
 
+  static bool WriteAllCowOps(size_t block_size,
+                             const std::vector<CowOperation>& converted,
+                             android::snapshot::ICowWriter* cow_writer,
+                             FileDescriptorPtr source_fd);
+
  private:
   std::unique_ptr<android::snapshot::ISnapshotWriter> cow_writer_;
 };