AU: Speed up updates by using buffered writes.
Given that SSD writes are really slow, this improves performance significantly.
This reduces update time on AGZ from 375 to 100 seconds.
BUG=6901
TEST=unit tests, gmerged on device and measured speed
Change-Id: Idac7743f6eaa8f26878a2d1f6b9401513e2ca600
Review URL: http://codereview.chromium.org/3471006
diff --git a/buffered_file_writer.cc b/buffered_file_writer.cc
new file mode 100644
index 0000000..03b8c77
--- /dev/null
+++ b/buffered_file_writer.cc
@@ -0,0 +1,60 @@
+// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "update_engine/buffered_file_writer.h"
+
+namespace chromeos_update_engine {
+
+BufferedFileWriter::BufferedFileWriter(FileWriter* next, size_t buffer_size)
+ : next_(next),
+ buffer_(new char[buffer_size]),
+ buffer_size_(buffer_size),
+ buffered_bytes_(0) {}
+
+BufferedFileWriter::~BufferedFileWriter() {}
+
+int BufferedFileWriter::Open(const char* path, int flags, mode_t mode) {
+ return next_->Open(path, flags, mode);
+}
+
+ssize_t BufferedFileWriter::Write(const void* bytes, size_t count) {
+ size_t copied_bytes = 0;
+ while (copied_bytes < count) {
+ // Buffers as many bytes as possible.
+ size_t remaining_free = buffer_size_ - buffered_bytes_;
+ size_t copy_bytes = count - copied_bytes;
+ if (copy_bytes > remaining_free) {
+ copy_bytes = remaining_free;
+ }
+ const char* char_bytes = reinterpret_cast<const char*>(bytes);
+ memcpy(&buffer_[buffered_bytes_], char_bytes + copied_bytes, copy_bytes);
+ buffered_bytes_ += copy_bytes;
+ copied_bytes += copy_bytes;
+
+ // If full, sends the buffer to the next FileWriter.
+ if (buffered_bytes_ == buffer_size_) {
+ ssize_t rc = WriteBuffer();
+ if (rc < 0)
+ return rc;
+ }
+ }
+ return count;
+}
+
+int BufferedFileWriter::Close() {
+ // Flushes the buffer first, then closes the next FileWriter.
+ ssize_t rc_write = WriteBuffer();
+ int rc_close = next_->Close();
+ return (rc_write < 0) ? rc_write : rc_close;
+}
+
+ssize_t BufferedFileWriter::WriteBuffer() {
+ if (buffered_bytes_ == 0)
+ return 0;
+ ssize_t rc = next_->Write(&buffer_[0], buffered_bytes_);
+ buffered_bytes_ = 0;
+ return rc;
+}
+
+} // namespace chromeos_update_engine