diff --git a/aosp/dynamic_partition_control_android.cc b/aosp/dynamic_partition_control_android.cc
index e1f86d8..1db8da8 100644
--- a/aosp/dynamic_partition_control_android.cc
+++ b/aosp/dynamic_partition_control_android.cc
@@ -49,6 +49,7 @@
 #include "update_engine/common/dynamic_partition_control_interface.h"
 #include "update_engine/common/platform_constants.h"
 #include "update_engine/common/utils.h"
+#include "update_engine/payload_consumer/cow_writer_file_descriptor.h"
 #include "update_engine/payload_consumer/delta_performer.h"
 
 using android::base::GetBoolProperty;
@@ -1329,7 +1330,7 @@
   return snapshot_->OpenSnapshotWriter(params, std::move(source_path));
 }  // namespace chromeos_update_engine
 
-FileDescriptorPtr DynamicPartitionControlAndroid::OpenCowReader(
+FileDescriptorPtr DynamicPartitionControlAndroid::OpenCowFd(
     const std::string& unsuffixed_partition_name,
     const std::optional<std::string>& source_path,
     bool is_append) {
@@ -1338,8 +1339,10 @@
   if (cow_writer == nullptr) {
     return nullptr;
   }
-  cow_writer->InitializeAppend(kEndOfInstallLabel);
-  return cow_writer->OpenReader();
+  if (!cow_writer->InitializeAppend(kEndOfInstallLabel)) {
+    return nullptr;
+  }
+  return std::make_shared<CowWriterFileDescriptor>(std::move(cow_writer));
 }
 
 std::optional<base::FilePath> DynamicPartitionControlAndroid::GetSuperDevice() {
diff --git a/aosp/dynamic_partition_control_android.h b/aosp/dynamic_partition_control_android.h
index 4e75a9b..c506ac9 100644
--- a/aosp/dynamic_partition_control_android.h
+++ b/aosp/dynamic_partition_control_android.h
@@ -104,9 +104,9 @@
       const std::string& unsuffixed_partition_name,
       const std::optional<std::string>& source_path,
       bool is_append) override;
-  FileDescriptorPtr OpenCowReader(const std::string& unsuffixed_partition_name,
-                                  const std::optional<std::string>&,
-                                  bool is_append = false) override;
+  FileDescriptorPtr OpenCowFd(const std::string& unsuffixed_partition_name,
+                              const std::optional<std::string>&,
+                              bool is_append = false) override;
 
   bool UnmapAllPartitions() override;
 
diff --git a/aosp/mock_dynamic_partition_control_android.h b/aosp/mock_dynamic_partition_control_android.h
index d80dfb5..428b6c7 100644
--- a/aosp/mock_dynamic_partition_control_android.h
+++ b/aosp/mock_dynamic_partition_control_android.h
@@ -95,7 +95,7 @@
                bool is_append),
               (override));
   MOCK_METHOD(FileDescriptorPtr,
-              OpenCowReader,
+              OpenCowFd,
               (const std::string& unsuffixed_partition_name,
                const std::optional<std::string>& source_path,
                bool is_append),
diff --git a/common/dynamic_partition_control_interface.h b/common/dynamic_partition_control_interface.h
index da27932..d5e1d8d 100644
--- a/common/dynamic_partition_control_interface.h
+++ b/common/dynamic_partition_control_interface.h
@@ -165,7 +165,9 @@
       const std::string& unsuffixed_partition_name,
       const std::optional<std::string>&,
       bool is_append = false) = 0;
-  virtual FileDescriptorPtr OpenCowReader(
+  // Open a general purpose FD capable to reading and writing to COW. Note that
+  // writes must be block aligned.
+  virtual FileDescriptorPtr OpenCowFd(
       const std::string& unsuffixed_partition_name,
       const std::optional<std::string>&,
       bool is_append = false) = 0;
diff --git a/common/dynamic_partition_control_stub.cc b/common/dynamic_partition_control_stub.cc
index 05803fe..dd30a8b 100644
--- a/common/dynamic_partition_control_stub.cc
+++ b/common/dynamic_partition_control_stub.cc
@@ -98,13 +98,6 @@
   return nullptr;
 }
 
-FileDescriptorPtr DynamicPartitionControlStub::OpenCowReader(
-    const std::string& unsuffixed_partition_name,
-    const std::optional<std::string>&,
-    bool /*is_append */) {
-  return nullptr;
-}
-
 bool DynamicPartitionControlStub::MapAllPartitions() {
   return false;
 }
diff --git a/common/dynamic_partition_control_stub.h b/common/dynamic_partition_control_stub.h
index eb7154c..515ec7c 100644
--- a/common/dynamic_partition_control_stub.h
+++ b/common/dynamic_partition_control_stub.h
@@ -64,9 +64,12 @@
       const std::string& unsuffixed_partition_name,
       const std::optional<std::string>&,
       bool is_append) override;
-  FileDescriptorPtr OpenCowReader(const std::string& unsuffixed_partition_name,
-                                  const std::optional<std::string>&,
-                                  bool is_append = false) override;
+
+  FileDescriptorPtr OpenCowFd(const std::string& unsuffixed_partition_name,
+                              const std::optional<std::string>&,
+                              bool is_append = false) override {
+    return nullptr;
+  }
 
   bool MapAllPartitions() override;
   bool UnmapAllPartitions() override;
diff --git a/common/mock_dynamic_partition_control.h b/common/mock_dynamic_partition_control.h
index 391d3eb..bfd1b0c 100644
--- a/common/mock_dynamic_partition_control.h
+++ b/common/mock_dynamic_partition_control.h
@@ -37,7 +37,7 @@
   MOCK_METHOD(FeatureFlag, GetVirtualAbFeatureFlag, (), (override));
   MOCK_METHOD(bool, FinishUpdate, (bool), (override));
   MOCK_METHOD(FileDescriptorPtr,
-              OpenCowReader,
+              OpenCowFd,
               (const std::string& unsuffixed_partition_name,
                const std::optional<std::string>& source_path,
                bool is_append),
diff --git a/payload_consumer/filesystem_verifier_action.cc b/payload_consumer/filesystem_verifier_action.cc
index aa2fbaa..4efbe41 100644
--- a/payload_consumer/filesystem_verifier_action.cc
+++ b/payload_consumer/filesystem_verifier_action.cc
@@ -129,8 +129,8 @@
   const InstallPlan::Partition& partition =
       install_plan_.partitions[partition_index_];
 
-  read_fd_ = dynamic_control_->OpenCowReader(
-      partition.name, partition.source_path, true);
+  read_fd_ =
+      dynamic_control_->OpenCowFd(partition.name, partition.source_path, true);
   if (!read_fd_) {
     LOG(ERROR) << "OpenCowReader(" << partition.name << ", "
                << partition.source_path << ") failed.";
diff --git a/payload_consumer/filesystem_verifier_action_unittest.cc b/payload_consumer/filesystem_verifier_action_unittest.cc
index 7d3ee9e..60e36cc 100644
--- a/payload_consumer/filesystem_verifier_action_unittest.cc
+++ b/payload_consumer/filesystem_verifier_action_unittest.cc
@@ -423,14 +423,13 @@
       .WillByDefault(Return(FeatureFlag(FeatureFlag::Value::LAUNCH)));
   ON_CALL(dynamic_control, UpdateUsesSnapshotCompression())
       .WillByDefault(Return(true));
-  ON_CALL(dynamic_control, OpenCowReader(_, _, _))
-      .WillByDefault(Return(fake_fd));
+  ON_CALL(dynamic_control, OpenCowFd(_, _, _)).WillByDefault(Return(fake_fd));
   ON_CALL(dynamic_control, IsDynamicPartition(part.name, _))
       .WillByDefault(Return(true));
 
   EXPECT_CALL(dynamic_control, UpdateUsesSnapshotCompression())
       .Times(AtLeast(1));
-  EXPECT_CALL(dynamic_control, OpenCowReader(part.name, {part.source_path}, _))
+  EXPECT_CALL(dynamic_control, OpenCowFd(part.name, {part.source_path}, _))
       .Times(1);
   EXPECT_CALL(dynamic_control, ListDynamicPartitionsForSlot(_, _, _))
       .WillRepeatedly(