AU: Extent writer utility classes
These are similar to the FileWriter classes, but focus on writing to
extents within a file (or device) rather than writing a file in order.
Again there is a ExtentWriter interface from which all types of extent
writers interit.
There are also two basic extent writers: a direct extent writer that
writes data directly to the file descriptor, and a zero padding extent
writer that piggy-backs on another extent writer. When the
zero-padding extent writer is End()ed, it fills out the rest of the
extent with zeros.
Also, BzipExtentWriter: an ExtentWriter concrete subclass that writes
to another ExtentWriter. BzipExtentWriter bzip2 decompresses all data
passed through.
Review URL: http://codereview.chromium.org/551132
diff --git a/extent_writer.cc b/extent_writer.cc
new file mode 100644
index 0000000..1ae565b
--- /dev/null
+++ b/extent_writer.cc
@@ -0,0 +1,67 @@
+// Copyright (c) 2009 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/extent_writer.h"
+#include <errno.h>
+#include <unistd.h>
+#include <algorithm>
+
+using std::min;
+
+namespace chromeos_update_engine {
+
+namespace {
+// Returns true on success.
+bool WriteAll(int fd, const void *buf, size_t count) {
+ const char* c_buf = reinterpret_cast<const char*>(buf);
+ ssize_t bytes_written = 0;
+ while (bytes_written < static_cast<ssize_t>(count)) {
+ ssize_t rc = write(fd, c_buf + bytes_written, count - bytes_written);
+ TEST_AND_RETURN_FALSE_ERRNO(rc >= 0);
+ bytes_written += rc;
+ }
+ return true;
+}
+}
+
+bool DirectExtentWriter::Write(const void* bytes, size_t count) {
+ if (count == 0)
+ return true;
+ const char* c_bytes = reinterpret_cast<const char*>(bytes);
+ size_t bytes_written = 0;
+ while (count - bytes_written > 0) {
+ TEST_AND_RETURN_FALSE(next_extent_index_ < extents_.size());
+ uint64 bytes_remaining_next_extent =
+ extents_[next_extent_index_].num_blocks() * block_size_ -
+ extent_bytes_written_;
+ CHECK_NE(bytes_remaining_next_extent, 0);
+ size_t bytes_to_write =
+ static_cast<size_t>(min(static_cast<uint64>(count - bytes_written),
+ bytes_remaining_next_extent));
+ TEST_AND_RETURN_FALSE(bytes_to_write > 0);
+
+ if (extents_[next_extent_index_].start_block() != kSparseHole) {
+ const off64_t offset =
+ extents_[next_extent_index_].start_block() * block_size_ +
+ extent_bytes_written_;
+ TEST_AND_RETURN_FALSE_ERRNO(lseek64(fd_, offset, SEEK_SET) !=
+ static_cast<off64_t>(-1));
+ TEST_AND_RETURN_FALSE(
+ WriteAll(fd_, c_bytes + bytes_written, bytes_to_write));
+ }
+ bytes_written += bytes_to_write;
+ extent_bytes_written_ += bytes_to_write;
+ if (bytes_remaining_next_extent == bytes_to_write) {
+ // We filled this extent
+ CHECK_EQ(extent_bytes_written_,
+ extents_[next_extent_index_].num_blocks() * block_size_);
+ // move to next extent
+ extent_bytes_written_ = 0;
+ next_extent_index_++;
+ }
+ }
+ return true;
+}
+
+} // namespace chromeos_update_engine