snapuserd: Remove ambiguous BufferSink in workers.

BufferSink is not needed/used in all worker types, so move it explicitly
to MergeWorker. This also moves the sizeof(dm_user_header) computation
to BufferSink::Initialize.

Bug: 288273605
Test: snapuserd_test
Change-Id: I8fcea6f0e587ca6d8672df5ec58c4d4d14d4b72e
diff --git a/fs_mgr/libsnapshot/snapuserd/dm_user_block_server.cpp b/fs_mgr/libsnapshot/snapuserd/dm_user_block_server.cpp
index ae62bc6..b5fef47 100644
--- a/fs_mgr/libsnapshot/snapuserd/dm_user_block_server.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/dm_user_block_server.cpp
@@ -27,7 +27,7 @@
 DmUserBlockServer::DmUserBlockServer(const std::string& misc_name, unique_fd&& ctrl_fd,
                                      Delegate* delegate, size_t buffer_size)
     : misc_name_(misc_name), ctrl_fd_(std::move(ctrl_fd)), delegate_(delegate) {
-    buffer_.Initialize(sizeof(struct dm_user_header) + buffer_size);
+    buffer_.Initialize(buffer_size);
 }
 
 bool DmUserBlockServer::ProcessRequests() {
diff --git a/fs_mgr/libsnapshot/snapuserd/snapuserd_buffer.cpp b/fs_mgr/libsnapshot/snapuserd/snapuserd_buffer.cpp
index 35065e6..490c0e6 100644
--- a/fs_mgr/libsnapshot/snapuserd/snapuserd_buffer.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/snapuserd_buffer.cpp
@@ -23,9 +23,9 @@
 namespace snapshot {
 
 void BufferSink::Initialize(size_t size) {
-    buffer_size_ = size;
+    buffer_size_ = size + sizeof(struct dm_user_header);
     buffer_offset_ = 0;
-    buffer_ = std::make_unique<uint8_t[]>(size);
+    buffer_ = std::make_unique<uint8_t[]>(buffer_size_);
 }
 
 void* BufferSink::AcquireBuffer(size_t size, size_t to_write) {
diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp b/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp
index 2305a1c..a83cab8 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp
@@ -556,6 +556,8 @@
 
     SNAP_LOG(INFO) << "Merge starting..";
 
+    bufsink_.Initialize(PAYLOAD_BUFFER_SZ);
+
     if (!Init()) {
         SNAP_LOG(ERROR) << "Merge thread initialization failed...";
         snapuserd_->MergeFailed();
diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.h b/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.h
index f35147f..478d4c8 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.h
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.h
@@ -39,6 +39,7 @@
     void FinalizeIouring();
 
   private:
+    BufferSink bufsink_;
     std::unique_ptr<ICowOpIter> cowop_iter_;
     std::unique_ptr<struct io_uring> ring_;
     size_t ra_block_index_ = 0;
diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/worker.cpp b/fs_mgr/libsnapshot/snapuserd/user-space-merge/worker.cpp
index aa15630..65208fb 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/worker.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/worker.cpp
@@ -27,18 +27,7 @@
     snapuserd_ = snapuserd;
 }
 
-void Worker::InitializeBufsink() {
-    // Allocate the buffer which is used to communicate between
-    // daemon and dm-user. The buffer comprises of header and a fixed payload.
-    // If the dm-user requests a big IO, the IO will be broken into chunks
-    // of PAYLOAD_BUFFER_SZ.
-    size_t buf_size = sizeof(struct dm_user_header) + PAYLOAD_BUFFER_SZ;
-    bufsink_.Initialize(buf_size);
-}
-
 bool Worker::Init() {
-    InitializeBufsink();
-
     if (!InitializeFds()) {
         return false;
     }
diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/worker.h b/fs_mgr/libsnapshot/snapuserd/user-space-merge/worker.h
index 813b159..c89d1b4 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/worker.h
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/worker.h
@@ -40,14 +40,11 @@
     virtual bool Init();
 
   protected:
-    // Initialization
-    void InitializeBufsink();
     bool InitializeFds();
     bool InitReader();
     virtual void CloseFds() { base_path_merge_fd_ = {}; }
 
     std::unique_ptr<CowReader> reader_;
-    BufferSink bufsink_;
 
     std::string misc_name_;  // Needed for SNAP_LOG.