AU: Delta Diff Generator

src/platform/update_engine/delta_diff_generator.cc

Index: src/platform/update_engine/delta_diff_generator.cc
diff --git a/src/platform/update_engine/delta_diff_generator.cc b/src/platform/update_engine/delta_diff_generator.cc
index 4114c3229e182722c1b8a71ee3f3fe92ba3ba3f6..4181057b0abd5093b989f7f92b427b4fa0eeab04 100644
--- a/src/platform/update_engine/delta_diff_generator.cc
+++ b/src/platform/update_engine/delta_diff_generator.cc
@@ -3,3 +3,863 @@
 // found in the LICENSE file.
 
 #include "update_engine/delta_diff_generator.h"
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <algorithm>
+#include <set>
+#include <string>
+#include <utility>
+#include <vector>
+#include <bzlib.h>
+#include "chromeos/obsolete_logging.h"
+#include "update_engine/bzip.h"
+#include "update_engine/cycle_breaker.h"
+#include "update_engine/extent_mapper.h"
+#include "update_engine/file_writer.h"
+#include "update_engine/filesystem_iterator.h"
+#include "update_engine/graph_types.h"
+#include "update_engine/graph_utils.h"
+#include "update_engine/subprocess.h"
+#include "update_engine/topological_sort.h"
+#include "update_engine/update_metadata.pb.h"
+#include "update_engine/utils.h"
+
+using std::make_pair;
+using std::min;
+using std::set;
+using std::string;
+using std::vector;
+
+namespace chromeos_update_engine {
+
+typedef DeltaDiffGenerator::Block Block;
+
+namespace {
+const size_t kBlockSize = 4096;
+const char* const kBsdiffPath = "/usr/bin/bsdiff";
+const uint64 kVersionNumber = 1;
+const char* const kDeltaMagic = "CrAU";
+
+// Stores all Extents for a file into 'out'. Returns true on success.
+bool GatherExtents(const string& path,
+                   google::protobuf::RepeatedPtrField<Extent>* out) {
+  vector<Extent> extents;
+  TEST_AND_RETURN_FALSE(extent_mapper::ExtentsForFileFibmap(path, &extents));
+  DeltaDiffGenerator::StoreExtents(extents, out);
+  return true;
+}
+
+// Runs the bsdiff tool on two files and returns the resulting delta in
+// 'out'. Returns true on success.
+bool BsdiffFiles(const string& old_file,
+                 const string& new_file,
+                 vector<char>* out) {
+  const string kPatchFile = "/tmp/delta.patchXXXXXX";
+  string patch_file_path;
+
+  TEST_AND_RETURN_FALSE(
+      utils::MakeTempFile(kPatchFile, &patch_file_path, NULL));
+
+  vector<string> cmd;
+  cmd.push_back(kBsdiffPath);
+  cmd.push_back(old_file);
+  cmd.push_back(new_file);
+  cmd.push_back(patch_file_path);
+
+  int rc = 1;
+  vector<char> patch_file;
+  TEST_AND_RETURN_FALSE(Subprocess::SynchronousExec(cmd, &rc));
+  TEST_AND_RETURN_FALSE(rc == 0);
+  TEST_AND_RETURN_FALSE(utils::ReadFile(patch_file_path, out));
+  unlink(patch_file_path.c_str());
+  return true;
+}
+
+// The blocks vector contains a reader and writer for each block on the
+// filesystem that's being in-place updated. We populate the reader/writer
+// fields of blocks by calling this function.
+// For each block in 'operation' that is read or written, find that block
+// in 'blocks' and set the reader/writer field to the vertex passed.
+// 'graph' is not strictly necessary, but useful for printing out
+// error messages.
+bool AddInstallOpToBlocksVector(
+    const DeltaArchiveManifest_InstallOperation& operation,
+    vector<Block>* blocks,
+    const Graph& graph,
+    Vertex::Index vertex) {
+  LOG(INFO) << "AddInstallOpToBlocksVector(" << vertex << "), "
+            << graph[vertex].file_name;
+  // See if this is already present.
+  TEST_AND_RETURN_FALSE(operation.dst_extents_size() > 0);
+  
+  enum BlockField { READER = 0, WRITER, BLOCK_FIELD_COUNT };
+  for (int field = READER; field < BLOCK_FIELD_COUNT; field++) {
+    const int extents_size =
+        (field == READER) ? operation.src_extents_size() :
+        operation.dst_extents_size();
+    const char* past_participle = (field == READER) ? "read" : "written";
+    const google::protobuf::RepeatedPtrField<Extent>& extents =
+        (field == READER) ? operation.src_extents() : operation.dst_extents();
+    Vertex::Index Block::*access_type =
+        (field == READER) ? &Block::reader : &Block::writer;
+
+    for (int i = 0; i < extents_size; i++) {
+      const Extent& extent = extents.Get(i);
+      if (extent.start_block() == kSparseHole) {
+        // Hole in sparse file. skip
+        continue;
+      }
+      for (uint64_t block = extent.start_block();
+           block < (extent.start_block() + extent.num_blocks()); block++) {
+        LOG(INFO) << "ext: " << i << " block: " << block;
+        if ((*blocks)[block].*access_type != Vertex::kInvalidIndex) {
+          LOG(FATAL) << "Block " << block << " is already "
+                     << past_participle << " by "
+                     << (*blocks)[block].*access_type << "("
+                     << graph[(*blocks)[block].*access_type].file_name
+                     << ") and also " << vertex << "("
+                     << graph[vertex].file_name << ")";
+        }
+        (*blocks)[block].*access_type = vertex;
+      }
+    }
+  }
+  return true;
+}
+
+// For a given regular file which must exist at new_root + path, and may
+// exist at old_root + path, creates a new InstallOperation and adds it to
+// the graph. Also, populates the 'blocks' array as necessary.
+// Also, writes the data necessary to send the file down to the client
+// into data_fd, which has length *data_file_size. *data_file_size is
+// updated appropriately.
+// Returns true on success.
+bool DeltaReadFile(Graph* graph,
+                   vector<Block>* blocks,
+                   const string& old_root,
+                   const string& new_root,
+                   const string& path,  // within new_root
+                   int data_fd,
+                   off_t* data_file_size) {
+  vector<char> data;
+  DeltaArchiveManifest_InstallOperation operation;
+
+  TEST_AND_RETURN_FALSE(DeltaDiffGenerator::ReadFileToDiff(old_root + path,
+                                                           new_root + path,
+                                                           &data,
+                                                           &operation));
+
+  // Write the data
+  if (operation.type() != DeltaArchiveManifest_InstallOperation_Type_MOVE) {
+    operation.set_data_offset(*data_file_size);
+    operation.set_data_length(data.size());
+  }
+
+  TEST_AND_RETURN_FALSE(utils::WriteAll(data_fd, &data[0], data.size()));
+  *data_file_size += data.size();
+  
+  // Now, insert into graph and blocks vector
+  graph->resize(graph->size() + 1);
+  graph->back().op = operation;
+  CHECK(graph->back().op.has_type());
+  graph->back().file_name = path;
+  
+  TEST_AND_RETURN_FALSE(AddInstallOpToBlocksVector(graph->back().op,
+                                                   blocks,
+                                                   *graph,
+                                                   graph->size() - 1));
+  return true;
+}
+
+// For each regular file within new_root, creates a node in the graph,
+// determines the best way to compress it (REPLACE, REPLACE_BZ, COPY, BSDIFF),
+// and writes any necessary data to the end of data_fd.
+bool DeltaReadFiles(Graph* graph,
+                    vector<Block>* blocks,
+                    const string& old_root,
+                    const string& new_root,
+                    int data_fd,
+                    off_t* data_file_size) {
+  set<ino_t> visited_inodes;
+  for (FilesystemIterator fs_iter(new_root,
+                                  utils::SetWithValue<string>("/lost+found"));
+       !fs_iter.IsEnd(); fs_iter.Increment()) {
+    if (!S_ISREG(fs_iter.GetStat().st_mode))
+      continue;
+
+    // Make sure we visit each inode only once.
+    if (utils::SetContainsKey(visited_inodes, fs_iter.GetStat().st_ino))
+      continue;
+    visited_inodes.insert(fs_iter.GetStat().st_ino);
+    if (fs_iter.GetStat().st_size == 0)
+      continue;
+
+    LOG(INFO) << "Encoding file " << fs_iter.GetPartialPath();
+    
+    TEST_AND_RETURN_FALSE(DeltaReadFile(graph,
+                                        blocks,
+                                        old_root,
+                                        new_root,
+                                        fs_iter.GetPartialPath(),
+                                        data_fd,
+                                        data_file_size));
+  }
+  return true;
+}
+
+// Attempts to find block_count blocks to use as scratch space.
+// Returns true on success.
+// Right now we return exactly as many blocks as are required.
+// TODO(adlr): consider returning all scratch blocks,
+// even if there are extras, to make it easier for a scratch allocator
+// to find contiguous regions for specific scratch writes.
+bool FindScratchSpace(const vector<Block>& blocks,
+                      vector<Block>::size_type block_count,
+                      vector<Extent>* out) {
+  // Scan blocks for blocks that are neither read nor written.
+  // If we don't find enough of those, return false.
+  // TODO(adlr): return blocks that are written by
+  // operations that don't have incoming edges (and thus, can be
+  // deferred until all old blocks are read by other operations).
+  vector<Extent> ret;
+  vector<Block>::size_type blocks_found = 0;
+  for (vector<Block>::size_type i = 0;
+       i < blocks.size() && blocks_found < block_count; i++) {
+    if (blocks[i].reader == Vertex::kInvalidIndex &&
+        blocks[i].writer == Vertex::kInvalidIndex) {
+      graph_utils::AppendBlockToExtents(&ret, i);
+      blocks_found++;
+    }
+  }
+  if (blocks_found == block_count) {
+    LOG(INFO) << "returning " << blocks_found << " scratch blocks";
+    out->swap(ret);
+    return true;
+  }
+  return false;
+}
+
+// This class takes a collection of Extents and allows the client to
+// allocate space from these extents. The client must not request more
+// space then exists in the source extents. Space is allocated from the
+// beginning of the source extents on; no consideration is paid to
+// fragmentation.
+class LinearExtentAllocator {
+ public:
+  explicit LinearExtentAllocator(const vector<Extent>& extents)
+      : extents_(extents),
+        extent_index_(0),
+        extent_blocks_allocated_(0) {}
+  vector<Extent> Allocate(const uint64_t block_count) {
+    vector<Extent> ret;
+    for (uint64_t blocks = 0; blocks < block_count; blocks++) {
+      CHECK_LT(extent_index_, extents_.size());
+      CHECK_LT(extent_blocks_allocated_, extents_[extent_index_].num_blocks());
+      graph_utils::AppendBlockToExtents(
+          &ret,
+          extents_[extent_index_].start_block() + extent_blocks_allocated_);
+      extent_blocks_allocated_++;
+      if (extent_blocks_allocated_ >= extents_[extent_index_].num_blocks()) {
+        extent_blocks_allocated_ = 0;
+        extent_index_++;
+      }
+    }
+    return ret;
+  }
+ private:
+  const vector<Extent> extents_;
+  vector<Extent>::size_type extent_index_;  // current Extent
+  // number of blocks allocated from the current extent
+  uint64_t extent_blocks_allocated_;
+};
+
+// Reads blocks from image_path that are not yet marked as being written
+// in the blocks array. These blocks that remain are non-file-data blocks.
+// In the future we might consider intelligent diffing between this data
+// and data in the previous image, but for now we just bzip2 compress it
+// and include it in the update.
+// Creates a new node in the graph to write these blocks and writes the
+// appropriate blob to blobs_fd. Reads and updates blobs_length;
+bool ReadUnwrittenBlocks(const vector<Block>& blocks,
+                         int blobs_fd,
+                         off_t* blobs_length,
+                         const string& image_path,
+                         DeltaArchiveManifest_InstallOperation* out_op) {
+  int image_fd = open(image_path.c_str(), O_RDONLY, 000);
+  TEST_AND_RETURN_FALSE_ERRNO(image_fd >= 0);
+  ScopedFdCloser image_fd_closer(&image_fd);
+
+  string temp_file_path;
+  TEST_AND_RETURN_FALSE(utils::MakeTempFile("/tmp/CrAU_temp_data.XXXXXX",
+                                            &temp_file_path,
+                                            NULL));
+
+  FILE* file = fopen(temp_file_path.c_str(), "w");
+  TEST_AND_RETURN_FALSE(file);
+  int err = BZ_OK;
+  
+  BZFILE* bz_file = BZ2_bzWriteOpen(&err,
+                                    file,
+                                    9,  // max compression
+                                    0,  // verbosity
+                                    0);  // default work factor
+  TEST_AND_RETURN_FALSE(err == BZ_OK);
+  
+  vector<Extent> extents;
+  vector<Block>::size_type block_count = 0;
+  
+  LOG(INFO) << "Appending left over blocks to extents";
+  for (vector<Block>::size_type i = 0; i < blocks.size(); i++) {
+    if (blocks[i].writer != Vertex::kInvalidIndex)
+      continue;
+    graph_utils::AppendBlockToExtents(&extents, i);
+    block_count++;
+  }
+
+  // Code will handle 'buf' at any size that's a multiple of kBlockSize,
+  // so we arbitrarily set it to 1024 * kBlockSize.
+  vector<char> buf(1024 * kBlockSize);
+
+  LOG(INFO) << "Reading left over blocks";
+  vector<Block>::size_type blocks_copied_count = 0;
+
+  // For each extent in extents, write the data into BZ2_bzWrite which
+  // sends it to an output file.
+  // We use the temporary buffer 'buf' to hold the data, which may be
+  // smaller than the extent, so in that case we have to loop to get
+  // the extent's data (that's the inner while loop).
+  for (vector<Extent>::const_iterator it = extents.begin();
+       it != extents.end(); ++it) {
+    vector<Block>::size_type blocks_read = 0;
+    while (blocks_read < it->num_blocks()) {
+      const int copy_block_cnt =
+          min(buf.size() / kBlockSize,
+              static_cast<vector<char>::size_type>(
+                  it->num_blocks() - blocks_read));
+      ssize_t rc = pread(image_fd,
+                         &buf[0],
+                         copy_block_cnt * kBlockSize,
+                         (it->start_block() + blocks_read) * kBlockSize);
+      TEST_AND_RETURN_FALSE_ERRNO(rc >= 0);
+      TEST_AND_RETURN_FALSE(static_cast<size_t>(rc) ==
+                            copy_block_cnt * kBlockSize);
+      BZ2_bzWrite(&err, bz_file, &buf[0], copy_block_cnt * kBlockSize);
+      TEST_AND_RETURN_FALSE(err == BZ_OK);
+      blocks_read += copy_block_cnt;
+      blocks_copied_count += copy_block_cnt;
+      LOG(INFO) << "progress: " << ((float)blocks_copied_count)/block_count;
+    }
+  }
+  BZ2_bzWriteClose(&err, bz_file, 0, NULL, NULL);
+  TEST_AND_RETURN_FALSE(err == BZ_OK);
+  bz_file = NULL;
+  TEST_AND_RETURN_FALSE_ERRNO(0 == fclose(file));
+  file = NULL;
+  
+  vector<char> compressed_data;
+  LOG(INFO) << "Reading compressed data off disk";
+  TEST_AND_RETURN_FALSE(utils::ReadFile(temp_file_path, &compressed_data));
+  TEST_AND_RETURN_FALSE(unlink(temp_file_path.c_str()) == 0);
+  
+  // Add node to graph to write these blocks
+  out_op->set_type(DeltaArchiveManifest_InstallOperation_Type_REPLACE_BZ);
+  out_op->set_data_offset(*blobs_length);
+  out_op->set_data_length(compressed_data.size());
+  *blobs_length += compressed_data.size();
+  out_op->set_dst_length(kBlockSize * block_count);
+  DeltaDiffGenerator::StoreExtents(extents, out_op->mutable_dst_extents());
+  
+  TEST_AND_RETURN_FALSE(utils::WriteAll(blobs_fd,
+                                        &compressed_data[0],
+                                        compressed_data.size()));
+  LOG(INFO) << "done with extra blocks";
+  return true;
+}
+
+// Writes the uint64 passed in in host-endian to the file as big-endian.
+// Returns true on success.
+bool WriteUint64AsBigEndian(FileWriter* writer, const uint64 value) {
+  uint64 value_be = htobe64(value);
+  TEST_AND_RETURN_FALSE(writer->Write(&value_be, sizeof(value_be)) ==
+                        sizeof(value_be));
+  return true;
+}
+
+// Adds each operation from the graph to the manifest in the order
+// specified by 'order'.
+void InstallOperationsToManifest(
+    const Graph& graph,
+    const vector<Vertex::Index>& order,
+    DeltaArchiveManifest* out_manifest) {
+  for (vector<Vertex::Index>::const_iterator it = order.begin();
+       it != order.end(); ++it) {
+    DeltaArchiveManifest_InstallOperation* op =
+        out_manifest->add_install_operations();
+    *op = graph[*it].op;
+  }
+}
+
+void CheckGraph(const Graph& graph) {
+  for (Graph::const_iterator it = graph.begin(); it != graph.end(); ++it) {
+    CHECK(it->op.has_type());
+  }
+}
+
+}  // namespace {}
+
+bool DeltaDiffGenerator::ReadFileToDiff(
+    const string& old_filename,
+    const string& new_filename,
+    vector<char>* out_data,
+    DeltaArchiveManifest_InstallOperation* out_op) {
+  // Read new data in
+  vector<char> new_data;
+  TEST_AND_RETURN_FALSE(utils::ReadFile(new_filename, &new_data));
+  
+  TEST_AND_RETURN_FALSE(!new_data.empty());
+  
+  vector<char> new_data_bz;
+  TEST_AND_RETURN_FALSE(BzipCompress(new_data, &new_data_bz));
+  CHECK(!new_data_bz.empty());
+
+  vector<char> data;  // Data blob that will be written to delta file.
+
+  DeltaArchiveManifest_InstallOperation operation;
+  size_t current_best_size = 0;
+  if (new_data.size() <= new_data_bz.size()) {
+    operation.set_type(DeltaArchiveManifest_InstallOperation_Type_REPLACE);
+    current_best_size = new_data.size();
+    data = new_data;
+  } else {
+    operation.set_type(DeltaArchiveManifest_InstallOperation_Type_REPLACE_BZ);
+    current_best_size = new_data_bz.size();
+    data = new_data_bz;
+  }
+
+  // Do we have an original file to consider?
+  struct stat old_stbuf;
+  if (0 != stat(old_filename.c_str(), &old_stbuf)) {
+    // If stat-ing the old file fails, it should be because it doesn't exist.
+    TEST_AND_RETURN_FALSE(errno == ENOTDIR || errno == ENOENT);
+  } else {
+    // Read old data
+    vector<char> old_data;
+    TEST_AND_RETURN_FALSE(utils::ReadFile(old_filename, &old_data));
+    if (old_data == new_data) {
+      // No change in data.
+      operation.set_type(DeltaArchiveManifest_InstallOperation_Type_MOVE);
+      current_best_size = 0;
+      data.clear();
+    } else {
+      // Try bsdiff of old to new data
+      vector<char> bsdiff_delta;
+      TEST_AND_RETURN_FALSE(
+          BsdiffFiles(old_filename, new_filename, &bsdiff_delta));
+      CHECK_GT(bsdiff_delta.size(), 0);
+      if (bsdiff_delta.size() < current_best_size) {
+        operation.set_type(DeltaArchiveManifest_InstallOperation_Type_BSDIFF);
+        current_best_size = bsdiff_delta.size();
+        
+        data = bsdiff_delta;
+      }
+    }
+  }
+  
+  // Set parameters of the operations
+  CHECK_EQ(data.size(), current_best_size);
+  
+  if (operation.type() == DeltaArchiveManifest_InstallOperation_Type_MOVE ||
+      operation.type() == DeltaArchiveManifest_InstallOperation_Type_BSDIFF) {
+    TEST_AND_RETURN_FALSE(
+        GatherExtents(old_filename, operation.mutable_src_extents()));
+    operation.set_src_length(old_stbuf.st_size);
+  }
+
+  TEST_AND_RETURN_FALSE(
+      GatherExtents(new_filename, operation.mutable_dst_extents()));
+  operation.set_dst_length(new_data.size());
+  
+  out_data->swap(data);
+  *out_op = operation;
+  
+  return true;
+}
+
+void DeltaDiffGenerator::SubstituteBlocks(
+    DeltaArchiveManifest_InstallOperation* op,
+    const vector<Extent>& remove_extents,
+    const vector<Extent>& replace_extents) {
+  // First, expand out the blocks that op reads from
+  vector<uint64> read_blocks;
+  for (int i = 0; i < op->src_extents_size(); i++) {
+    const Extent& extent = op->src_extents(i);
+    if (extent.start_block() == kSparseHole) {
+      read_blocks.resize(read_blocks.size() + extent.num_blocks(), kSparseHole);
+    } else {
+      for (uint64 block = extent.start_block();
+           block < (extent.start_block() + extent.num_blocks()); block++) {
+        read_blocks.push_back(block);
+      }
+    }
+  }
+  {
+    // Expand remove_extents and replace_extents
+    vector<uint64> remove_extents_expanded;
+    for (vector<Extent>::const_iterator it = remove_extents.begin();
+         it != remove_extents.end(); ++it) {
+      const Extent& extent = *it;
+      for (uint64 block = extent.start_block();
+           block < (extent.start_block() + extent.num_blocks()); block++) {
+        remove_extents_expanded.push_back(block);
+      }
+    }
+    vector<uint64> replace_extents_expanded;
+    for (vector<Extent>::const_iterator it = replace_extents.begin();
+         it != replace_extents.end(); ++it) {
+      const Extent& extent = *it;
+      for (uint64 block = extent.start_block();
+           block < (extent.start_block() + extent.num_blocks()); block++) {
+        replace_extents_expanded.push_back(block);
+      }
+    }
+    CHECK_EQ(remove_extents_expanded.size(), replace_extents_expanded.size());
+    for (vector<uint64>::size_type i = 0;
+         i < replace_extents_expanded.size(); i++) {
+      vector<uint64>::size_type index = 0;
+      CHECK(utils::VectorIndexOf(read_blocks,
+                                 remove_extents_expanded[i],
+                                 &index));
+      CHECK(read_blocks[index] == remove_extents_expanded[i]);
+      read_blocks[index] = replace_extents_expanded[i];
+    }
+  }
+  // Convert read_blocks back to extents
+  op->clear_src_extents();
+  vector<Extent> new_extents;
+  for (vector<uint64>::const_iterator it = read_blocks.begin();
+       it != read_blocks.end(); ++it) {
+    graph_utils::AppendBlockToExtents(&new_extents, *it);
+  }
+  DeltaDiffGenerator::StoreExtents(new_extents, op->mutable_src_extents());
+}
+
+bool DeltaDiffGenerator::CutEdges(Graph* graph,
+                                  const vector<Block>& blocks,
+                                  const set<Edge>& edges) {
+  // First, find enough scratch space for the edges we'll be cutting.
+  vector<Block>::size_type blocks_required = 0;
+  for (set<Edge>::const_iterator it = edges.begin(); it != edges.end(); ++it) {
+    blocks_required += graph_utils::EdgeWeight(*graph, *it);
+  }
+  vector<Extent> scratch_extents;
+  LOG(INFO) << "requesting " << blocks_required << " blocks of scratch";
+  TEST_AND_RETURN_FALSE(
+      FindScratchSpace(blocks, blocks_required, &scratch_extents));
+  LinearExtentAllocator scratch_allocator(scratch_extents);
+  
+  uint64_t scratch_blocks_used = 0;
+  for (set<Edge>::const_iterator it = edges.begin();
+       it != edges.end(); ++it) {
+    vector<Extent> old_extents =
+        (*graph)[it->first].out_edges[it->second].extents;
+    // Choose some scratch space
+    scratch_blocks_used += graph_utils::EdgeWeight(*graph, *it);
+    LOG(INFO) << "using " << graph_utils::EdgeWeight(*graph, *it)
+              << " scratch blocks ("
+              << scratch_blocks_used << ")";
+    vector<Extent> scratch =
+        scratch_allocator.Allocate(graph_utils::EdgeWeight(*graph, *it));
+    // create vertex to copy original->scratch
+    graph->resize(graph->size() + 1);
+    
+    // make node depend on the copy operation
+    (*graph)[it->first].out_edges.insert(make_pair(graph->size() - 1,
+                                                   EdgeProperties()));
+
+    // Set src/dst extents and other proto variables for copy operation
+    graph->back().op.set_type(DeltaArchiveManifest_InstallOperation_Type_MOVE);
+    DeltaDiffGenerator::StoreExtents(
+        (*graph)[it->first].out_edges[it->second].extents,
+        graph->back().op.mutable_src_extents());
+    DeltaDiffGenerator::StoreExtents(scratch,
+                                     graph->back().op.mutable_dst_extents());
+    graph->back().op.set_src_length(
+        graph_utils::EdgeWeight(*graph, *it) * kBlockSize);
+    graph->back().op.set_dst_length(graph->back().op.src_length());
+
+    // make the dest node read from the scratch space
+    DeltaDiffGenerator::SubstituteBlocks(
+        &((*graph)[it->second].op),
+        (*graph)[it->first].out_edges[it->second].extents,
+        scratch);
+
+    // delete the old edge
+    CHECK_EQ(1, (*graph)[it->first].out_edges.erase(it->second));
+  }
+  return true;
+}
+
+// Stores all Extents in 'extents' into 'out'.
+void DeltaDiffGenerator::StoreExtents(
+    vector<Extent>& extents,
+    google::protobuf::RepeatedPtrField<Extent>* out) {
+  for (vector<Extent>::const_iterator it = extents.begin();
+       it != extents.end(); ++it) {
+    Extent* new_extent = out->Add();
+    *new_extent = *it;
+  }
+}
+
+// Creates all the edges for the graph. Writers of a block point to
+// readers of the same block. This is because for an edge A->B, B
+// must complete before A executes.
+void DeltaDiffGenerator::CreateEdges(Graph* graph,
+                                     const vector<Block>& blocks) {
+  for (vector<Block>::size_type i = 0; i < blocks.size(); i++) {
+    // Blocks with both a reader and writer get an edge
+    if (blocks[i].reader == Vertex::kInvalidIndex ||
+        blocks[i].writer == Vertex::kInvalidIndex)
+      continue;
+    // Don't have a node depend on itself
+    if (blocks[i].reader == blocks[i].writer)
+      continue;
+    // See if there's already an edge we can add onto
+    Vertex::EdgeMap::iterator edge_it =
+        (*graph)[blocks[i].writer].out_edges.find(blocks[i].reader);
+    if (edge_it == (*graph)[blocks[i].writer].out_edges.end()) {
+      // No existing edge. Create one
+      (*graph)[blocks[i].writer].out_edges.insert(
+          make_pair(blocks[i].reader, EdgeProperties()));
+      edge_it = (*graph)[blocks[i].writer].out_edges.find(blocks[i].reader);
+      CHECK_NE(edge_it, (*graph)[blocks[i].writer].out_edges.end());
+    }
+    graph_utils::AppendBlockToExtents(&edge_it->second.extents, i);
+  }
+}
+
+bool DeltaDiffGenerator::ReorderDataBlobs(
+    DeltaArchiveManifest* manifest,
+    const std::string& data_blobs_path,
+    const std::string& new_data_blobs_path) {
+  int in_fd = open(data_blobs_path.c_str(), O_RDONLY, 0);
+  TEST_AND_RETURN_FALSE_ERRNO(in_fd >= 0);
+  ScopedFdCloser in_fd_closer(&in_fd);
+  
+  DirectFileWriter writer;
+  TEST_AND_RETURN_FALSE(
+      writer.Open(new_data_blobs_path.c_str(),
+                  O_WRONLY | O_TRUNC | O_CREAT,
+                  0644) == 0);
+  ScopedFileWriterCloser writer_closer(&writer);
+  uint64 out_file_size = 0;
+  
+  for (int i = 0; i < manifest->install_operations_size(); i++) {
+    DeltaArchiveManifest_InstallOperation* op =
+        manifest->mutable_install_operations(i);
+    if (!op->has_data_offset())
+      continue;
+    CHECK(op->has_data_length());
+    vector<char> buf(op->data_length());
+    ssize_t rc = pread(in_fd, &buf[0], buf.size(), op->data_offset());
+    TEST_AND_RETURN_FALSE(rc == static_cast<ssize_t>(buf.size()));
+
+    op->set_data_offset(out_file_size);
+    TEST_AND_RETURN_FALSE(writer.Write(&buf[0], buf.size()) ==
+                          static_cast<ssize_t>(buf.size()));
+    out_file_size += buf.size();
+  }
+  return true;
+}
+
+bool DeltaDiffGenerator::GenerateDeltaUpdateFile(const string& old_root,
+                                                 const string& old_image,
+                                                 const string& new_root,
+                                                 const string& new_image,
+                                                 const string& output_path) {
+  struct stat old_image_stbuf;
+  TEST_AND_RETURN_FALSE_ERRNO(stat(old_image.c_str(), &old_image_stbuf) == 0);
+  struct stat new_image_stbuf;
+  TEST_AND_RETURN_FALSE_ERRNO(stat(new_image.c_str(), &new_image_stbuf) == 0);
+  LOG_IF(WARNING, new_image_stbuf.st_size != old_image_stbuf.st_size)
+      << "Old and new images are different sizes.";
+  LOG_IF(FATAL, new_image_stbuf.st_size % kBlockSize)
+      << "New image not a multiple of block size " << kBlockSize;
+  LOG_IF(FATAL, old_image_stbuf.st_size % kBlockSize)
+      << "Old image not a multiple of block size " << kBlockSize;
+
+  vector<Block> blocks(min(old_image_stbuf.st_size / kBlockSize,
+                           new_image_stbuf.st_size / kBlockSize));
+  LOG(INFO) << "blocks (orig): " << (uint32)(&blocks);
+  LOG(INFO) << "w:" << blocks[4097].writer;
+  LOG(INFO) << "invalid: " << Vertex::kInvalidIndex;
+  LOG(INFO) << "len: " << blocks.size();
+  for (vector<Block>::size_type i = 0; i < blocks.size(); i++) {
+    CHECK(blocks[i].reader == Vertex::kInvalidIndex);
+    CHECK(blocks[i].writer == Vertex::kInvalidIndex);
+  }
+  Graph graph;
+  CheckGraph(graph);
+  
+  const string kTempFileTemplate("/tmp/CrAU_temp_data.XXXXXX");
+  string temp_file_path;
+  off_t data_file_size = 0;
+
+  LOG(INFO) << "Reading files...";
+
+  DeltaArchiveManifest_InstallOperation final_op;
+  {
+    int fd;
+    TEST_AND_RETURN_FALSE(
+        utils::MakeTempFile(kTempFileTemplate, &temp_file_path, &fd));
+    TEST_AND_RETURN_FALSE(fd >= 0);
+    ScopedFdCloser fd_closer(&fd);
+  
+    TEST_AND_RETURN_FALSE(DeltaReadFiles(&graph,
+                                         &blocks,
+                                         old_root,
+                                         new_root,
+                                         fd,
+                                         &data_file_size));
+    CheckGraph(graph);
+                                         
+    // TODO(adlr): read all the rest of the blocks in
+    TEST_AND_RETURN_FALSE(ReadUnwrittenBlocks(blocks,
+                                              fd,
+                                              &data_file_size,
+                                              new_image,
+                                              &final_op));  
+  }
+  CheckGraph(graph);
+  
+  LOG(INFO) << "Creating edges...";
+  CreateEdges(&graph, blocks);
+  CheckGraph(graph);
+  
+  CycleBreaker cycle_breaker;
+  LOG(INFO) << "Finding cycles...";
+  set<Edge> cut_edges;
+  cycle_breaker.BreakCycles(graph, &cut_edges);
+  CheckGraph(graph);
+
+  // Calculate number of scratch blocks needed
+
+  LOG(INFO) << "Cutting cycles...";
+  TEST_AND_RETURN_FALSE(CutEdges(&graph, blocks, cut_edges));
+  CheckGraph(graph);
+
+  vector<Vertex::Index> final_order;
+  LOG(INFO) << "Ordering...";
+  TopologicalSort(graph, &final_order);
+  CheckGraph(graph);
+  
+  // Convert to protobuf Manifest object
+  DeltaArchiveManifest manifest;
+  CheckGraph(graph);
+  InstallOperationsToManifest(graph, final_order, &manifest);
+  {
+    // Write final operation
+    DeltaArchiveManifest_InstallOperation* op =
+        manifest.add_install_operations();
+    *op = final_op;
+    CHECK(op->has_type());
+    LOG(INFO) << "final op length: " << op->data_length();
+  }
+  CheckGraph(graph);
+  manifest.set_block_size(kBlockSize);
+  // TODO(adlr): set checksums
+
+  // Reorder the data blobs with the newly ordered manifest
+  string ordered_blobs_path;
+  TEST_AND_RETURN_FALSE(utils::MakeTempFile(
+      "/tmp/CrAU_temp_data.ordered.XXXXXX",
+      &ordered_blobs_path,
+      false));
+  TEST_AND_RETURN_FALSE(ReorderDataBlobs(&manifest,
+                                         temp_file_path,
+                                         ordered_blobs_path));
+
+  // Check that install op blobs are in order and that all blocks are written.
+  {
+    vector<uint32> written_count(blocks.size(), 0);
+    uint64 next_blob_offset = 0;
+    for (int i = 0; i < manifest.install_operations_size(); i++) {
+      const DeltaArchiveManifest_InstallOperation& op =
+          manifest.install_operations(i);
+      for (int j = 0; j < op.dst_extents_size(); j++) {
+        const Extent& extent = op.dst_extents(j);
+        for (uint64 block = extent.start_block();
+             block < (extent.start_block() + extent.num_blocks()); block++) {
+          written_count[block]++;
+        }
+      }
+      if (op.has_data_offset()) {
+        if (op.data_offset() != next_blob_offset) {
+          LOG(FATAL) << "bad blob offset! " << op.data_offset() << " != "
+                     << next_blob_offset;
+        }
+        next_blob_offset += op.data_length();
+      }
+    }
+    // check all blocks written to
+    for (vector<uint32>::size_type i = 0; i < written_count.size(); i++) {
+      if (written_count[i] == 0) {
+        LOG(FATAL) << "block " << i << " not written!";
+      }
+    }
+  }
+
+  // Serialize protobuf
+  string serialized_manifest;
+  
+  CheckGraph(graph);
+  TEST_AND_RETURN_FALSE(manifest.AppendToString(&serialized_manifest));
+  CheckGraph(graph);
+
+  LOG(INFO) << "Writing final delta file header...";
+  DirectFileWriter writer;
+  TEST_AND_RETURN_FALSE_ERRNO(writer.Open(output_path.c_str(),
+                                          O_WRONLY | O_CREAT | O_TRUNC,
+                                          0644) == 0);
+  ScopedFileWriterCloser writer_closer(&writer);
+  
+  // Write header
+  TEST_AND_RETURN_FALSE(writer.Write(kDeltaMagic, strlen(kDeltaMagic)) ==
+                        strlen(kDeltaMagic));
+  
+  // Write version number
+  TEST_AND_RETURN_FALSE(WriteUint64AsBigEndian(&writer, kVersionNumber));
+  
+  // Write protobuf length
+  TEST_AND_RETURN_FALSE(WriteUint64AsBigEndian(&writer,
+                                               serialized_manifest.size()));
+  
+  // Write protobuf
+  LOG(INFO) << "Writing final delta file protobuf... "
+            << serialized_manifest.size();
+  TEST_AND_RETURN_FALSE(writer.Write(serialized_manifest.data(),
+                                     serialized_manifest.size()) ==
+                        static_cast<ssize_t>(serialized_manifest.size()));
+  
+  // Append the data blobs
+  LOG(INFO) << "Writing final delta file data blobs...";
+  int blobs_fd = open(temp_file_path.c_str(), O_RDONLY, 0);
+  ScopedFdCloser blobs_fd_closer(&blobs_fd);
+  TEST_AND_RETURN_FALSE(blobs_fd >= 0);
+  for (;;) {
+    char buf[kBlockSize];
+    ssize_t rc = read(blobs_fd, buf, sizeof(buf));
+    if (0 == rc) {
+      // EOF
+      break;
+    }
+    TEST_AND_RETURN_FALSE_ERRNO(rc > 0);
+    TEST_AND_RETURN_FALSE(writer.Write(buf, rc) == rc);
+  }
+  
+  LOG(INFO) << "All done. Successfully created delta file.";
+  return true;
+}
+
+};  // namespace chromeos_update_engine