sparse win file write (#398)

* Added `--use-sparse-files` option to `zen builds` command improving write performance of large files. Enabled by default.

2 files changed, 30 insertions, 0 deletions

diff --git a/src/zencore/filesystem.cpp b/src/zencore/filesystem.cpp
index 018330d9b..c1df6d53e 100644
--- a/src/zencore/filesystem.cpp
+++ b/src/zencore/filesystem.cpp
@@ -2158,6 +2158,34 @@ MaximizeOpenFileCount()
 #endif
 }
 
+bool
+PrepareFileForScatteredWrite(void* FileHandle, uint64_t FinalSize)
+{
+	bool Result = true;
+#if ZEN_PLATFORM_WINDOWS
+	DWORD _	 = 0;
+	BOOL  Ok = DeviceIoControl(FileHandle, FSCTL_SET_SPARSE, nullptr, 0, nullptr, 0, &_, nullptr);
+	if (!Ok)
+	{
+		std::error_code DummyEc;
+		ZEN_DEBUG("Unable to set sparse mode for file '{}'", PathFromHandle(FileHandle, DummyEc));
+		Result = false;
+	}
+
+	FILE_ALLOCATION_INFO AllocationInfo	   = {};
+	AllocationInfo.AllocationSize.QuadPart = FinalSize;
+	if (!SetFileInformationByHandle(FileHandle, FileAllocationInfo, &AllocationInfo, DWORD(sizeof(AllocationInfo))))
+	{
+		std::error_code DummyEc;
+		ZEN_DEBUG("Unable to set file allocation size to {} for file '{}'", FinalSize, PathFromHandle(FileHandle, DummyEc));
+		Result = false;
+	}
+#else	// ZEN_PLATFORM_WINDOWS
+	ZEN_UNUSED(FileHandle, FinalSize);
+#endif	// ZEN_PLATFORM_WINDOWS
+	return Result;
+}
+
 void
 GetDirectoryContent(const std::filesystem::path& RootDir, DirectoryContentFlags Flags, DirectoryContent& OutContent)
 {
diff --git a/src/zencore/include/zencore/filesystem.h b/src/zencore/include/zencore/filesystem.h
index 1bc3943df..e62170eba 100644
--- a/src/zencore/include/zencore/filesystem.h
+++ b/src/zencore/include/zencore/filesystem.h
@@ -137,6 +137,8 @@ ZENCORE_API std::filesystem::path GetRunningExecutablePath();
  */
 ZENCORE_API void MaximizeOpenFileCount();
 
+ZENCORE_API bool PrepareFileForScatteredWrite(void* FileHandle, uint64_t FinalSize);
+
 struct FileContents
 {
 	std::vector<IoBuffer> Data;