From 7e54d284e1b8d99d63304a5075a4597aa4787a8d Mon Sep 17 00:00:00 2001
From: Sebastian Messmer <mail@smessmer.de>
Date: Mon, 5 Oct 2015 02:55:04 +0200
Subject: [PATCH] Speed up writing back of DirBlobs by another factor of 3 (so
 9 in total) by serializing the whole blob and writing it back with one
 write() call

---
 src/filesystem/fsblobstore/DirBlob.cpp | 42 ++++++++++++++------------
 src/filesystem/fsblobstore/DirBlob.h   |  4 +--
 2 files changed, 25 insertions(+), 21 deletions(-)

diff --git a/src/filesystem/fsblobstore/DirBlob.cpp b/src/filesystem/fsblobstore/DirBlob.cpp
index cbb22273..a3a3f14a 100644
--- a/src/filesystem/fsblobstore/DirBlob.cpp
+++ b/src/filesystem/fsblobstore/DirBlob.cpp
@@ -47,47 +47,51 @@ unique_ref<DirBlob> DirBlob::InitializeEmptyDir(unique_ref<Blob> blob, std::func
   return make_unique_ref<DirBlob>(std::move(blob), getLstatSize);
 }
 
-Data DirBlob::_writeEntry(const DirBlob::Entry & entry) {
+size_t DirBlob::_serializedSizeOfEntry(const DirBlob::Entry &entry) {
+  return 1 + (entry.name.size() + 1) + (entry.key.STRING_LENGTH + 1) + sizeof(uid_t) + sizeof(gid_t) + sizeof(mode_t);
+}
+
+void DirBlob::_serializeEntry(const DirBlob::Entry & entry, uint8_t *dest) {
+  //TODO Write key as binary?
   string keystr = entry.key.ToString();
 
-  unsigned int size = 1 + (entry.name.size() + 1) + (keystr.size() + 1) + sizeof(uid_t) + sizeof(gid_t) + sizeof(mode_t);
-  Data result(size);
   unsigned int offset = 0;
-
-  *static_cast<uint8_t*>(result.dataOffset(offset)) = static_cast<uint8_t>(entry.type);
+  *(dest+offset) = static_cast<uint8_t>(entry.type);
   offset += 1;
 
-  std::memcpy(result.dataOffset(offset), entry.name.c_str(), entry.name.size()+1);
+  std::memcpy(dest+offset, entry.name.c_str(), entry.name.size()+1);
   offset += entry.name.size() + 1;
 
-  std::memcpy(result.dataOffset(offset), keystr.c_str(), keystr.size() + 1);
+  std::memcpy(dest+offset, keystr.c_str(), keystr.size() + 1);
   offset += keystr.size() + 1;
 
-  *reinterpret_cast<uid_t*>(result.dataOffset(offset)) = entry.uid;
+  *reinterpret_cast<uid_t*>(dest+offset) = entry.uid;
   offset += sizeof(uid_t);
 
-  *reinterpret_cast<gid_t*>(result.dataOffset(offset)) = entry.gid;
+  *reinterpret_cast<gid_t*>(dest+offset) = entry.gid;
   offset += sizeof(gid_t);
 
-  *reinterpret_cast<mode_t*>(result.dataOffset(offset)) = entry.mode;
+  *reinterpret_cast<mode_t*>(dest+offset) = entry.mode;
   offset += sizeof(mode_t);
 
-  ASSERT(offset == size, "Didn't write correct number of elements");
-
-  return result;
+  ASSERT(offset == _serializedSizeOfEntry(entry), "Didn't write correct number of elements");
 }
 
 void DirBlob::_writeEntriesToBlob() {
   std::unique_lock<std::mutex> lock(_mutex);
   if (_changed) {
-    //TODO Resizing is imperformant
-    baseBlob().resize(1);
-    unsigned int offset = 1;
+    size_t serializedSize = 0;
     for (const auto &entry : _entries) {
-      Data serializedEntry = _writeEntry(entry);
-      baseBlob().write(serializedEntry.data(), offset, serializedEntry.size());
-      offset += serializedEntry.size();
+      serializedSize += _serializedSizeOfEntry(entry);
     }
+    Data serialized(serializedSize);
+    unsigned int offset = 0;
+    for (const auto &entry : _entries) {
+      _serializeEntry(entry, static_cast<uint8_t*>(serialized.dataOffset(offset)));
+      offset += _serializedSizeOfEntry(entry);
+    }
+    baseBlob().resize(1 + serializedSize);
+    baseBlob().write(serialized.data(), 1, serializedSize);
     _changed = false;
   }
 }
diff --git a/src/filesystem/fsblobstore/DirBlob.h b/src/filesystem/fsblobstore/DirBlob.h
index 2c605cc7..2d643587 100644
--- a/src/filesystem/fsblobstore/DirBlob.h
+++ b/src/filesystem/fsblobstore/DirBlob.h
@@ -4,7 +4,6 @@
 
 #include <messmer/blockstore/utils/Key.h>
 #include <messmer/cpp-utils/macros.h>
-#include <messmer/cpp-utils/data/Data.h>
 #include <messmer/fspp/fs_interface/Dir.h>
 #include "FsBlob.h"
 #include <vector>
@@ -91,7 +90,8 @@ namespace cryfs {
             void _readEntriesFromBlob();
 
             void _writeEntriesToBlob();
-            static cpputils::Data _writeEntry(const DirBlob::Entry & entry);
+            static size_t _serializedSizeOfEntry(const DirBlob::Entry &entry);
+            static void _serializeEntry(const DirBlob::Entry &entry, uint8_t *dest);
 
             std::vector<DirBlob::Entry>::iterator _findChild(const blockstore::Key &key);