diff --git a/graph_types.h b/graph_types.h
index e7867f6..e3220c0 100644
--- a/graph_types.h
+++ b/graph_types.h
@@ -18,12 +18,28 @@
 
 namespace chromeos_update_engine {
 
+bool operator==(const Extent& a, const Extent& b);
+
 struct EdgeProperties {
-  std::vector<Extent> extents;  // filesystem extents represented
+  // Read-before extents. I.e., blocks in |extents| must be read by the
+  // node pointed to before the pointing node runs (presumably b/c it
+  // overwrites these blocks).
+  std::vector<Extent> extents;
+  
+  // Write before extents. I.e., blocks in |write_extents| must be written
+  // by the node pointed to before the pointing node runs (presumably
+  // b/c it reads the data written by the other node).
+  std::vector<Extent> write_extents;
+  
+  bool operator==(const EdgeProperties& that) const {
+    return extents == that.extents && write_extents == that.write_extents;
+  }
 };
 
 struct Vertex {
-  Vertex() : index(-1), lowlink(-1) {}
+  Vertex() : valid(true), index(-1), lowlink(-1) {}
+  bool valid;
+  
   typedef std::map<std::vector<Vertex>::size_type, EdgeProperties> EdgeMap;
   EdgeMap out_edges;
 
@@ -51,6 +67,8 @@
 typedef std::pair<Vertex::Index, Vertex::Index> Edge;
 
 const uint64_t kSparseHole = kuint64max;
+const uint64_t kTempBlockStart = 1ULL << 60;
+COMPILE_ASSERT(kTempBlockStart != 0, kTempBlockStart_invalid);
 
 }  // namespace chromeos_update_engine
 
diff --git a/graph_utils.cc b/graph_utils.cc
index 5ad67cf..47d0c53 100644
--- a/graph_utils.cc
+++ b/graph_utils.cc
@@ -3,8 +3,17 @@
 // found in the LICENSE file.
 
 #include "update_engine/graph_utils.h"
-#include "base/basictypes.h"
 
+#include <string>
+#include <utility>
+#include <vector>
+
+#include <base/basictypes.h>
+#include <base/logging.h>
+
+using std::make_pair;
+using std::pair;
+using std::string;
 using std::vector;
 
 namespace chromeos_update_engine {
@@ -45,6 +54,124 @@
   extents->push_back(new_extent);
 }
 
+void AddReadBeforeDep(Vertex* src,
+                      Vertex::Index dst,
+                      uint64_t block) {
+  Vertex::EdgeMap::iterator edge_it = src->out_edges.find(dst);
+  if (edge_it == src->out_edges.end()) {
+    // Must create new edge
+    pair<Vertex::EdgeMap::iterator, bool> result =
+        src->out_edges.insert(make_pair(dst, EdgeProperties()));
+    CHECK(result.second);
+    edge_it = result.first;
+  }
+  AppendBlockToExtents(&edge_it->second.extents, block);
+}
+
+void AddReadBeforeDepExtents(Vertex* src,
+                             Vertex::Index dst,
+                             const vector<Extent>& extents) {
+  // TODO(adlr): Be more efficient than adding each block individually.
+  for (vector<Extent>::const_iterator it = extents.begin(), e = extents.end();
+       it != e; ++it) {
+    const Extent& extent = *it;
+    for (uint64_t block = extent.start_block(),
+             block_end = extent.start_block() + extent.num_blocks();
+         block != block_end; ++block) {
+      AddReadBeforeDep(src, dst, block);
+    }
+  }
+}
+
+void DropWriteBeforeDeps(Vertex::EdgeMap* edge_map) {
+  // Specially crafted for-loop for the map-iterate-delete dance.
+  for (Vertex::EdgeMap::iterator it = edge_map->begin();
+       it != edge_map->end(); ) {
+    if (!it->second.write_extents.empty())
+      it->second.write_extents.clear();
+    if (it->second.extents.empty()) {
+      // Erase *it, as it contains no blocks
+      edge_map->erase(it++);
+    } else {
+      ++it;
+    }
+  }
+}
+
+// For each node N in graph, drop all edges N->|index|.
+void DropIncomingEdgesTo(Graph* graph, Vertex::Index index) {
+  // This would be much more efficient if we had doubly-linked
+  // edges in the graph.
+  for (Graph::iterator it = graph->begin(), e = graph->end(); it != e; ++it) {
+    it->out_edges.erase(index);
+  }
+}
+
+Extent GetElement(const std::vector<Extent>& collection, size_t index) {
+  return collection[index];
+}
+Extent GetElement(
+    const google::protobuf::RepeatedPtrField<Extent>& collection,
+    size_t index) {
+  return collection.Get(index);
+}
+
+namespace {
+template<typename T>
+void DumpExtents(const T& field, int prepend_space_count) {
+  string header(prepend_space_count, ' ');
+  for (int i = 0, e = field.size(); i != e; ++i) {
+    LOG(INFO) << header << "(" << GetElement(field, i).start_block() << ", "
+              << GetElement(field, i).num_blocks() << ")";
+  }
+}
+
+void DumpOutEdges(const Vertex::EdgeMap& out_edges) {
+  for (Vertex::EdgeMap::const_iterator it = out_edges.begin(),
+           e = out_edges.end(); it != e; ++it) {
+    LOG(INFO) << "    " << it->first << " read-before:";
+    DumpExtents(it->second.extents, 6);
+    LOG(INFO) << "      write-before:";
+    DumpExtents(it->second.write_extents, 6);
+  }
+}
+}  // namespace {}
+
+void DumpGraph(const Graph& graph) {
+  LOG(INFO) << "Graph length: " << graph.size();
+  for (Graph::size_type i = 0, e = graph.size(); i != e; ++i) {
+    string type_str = "UNK";
+    switch(graph[i].op.type()) {
+      case DeltaArchiveManifest_InstallOperation_Type_BSDIFF:
+        type_str = "BSDIFF";
+        break;
+      case DeltaArchiveManifest_InstallOperation_Type_MOVE:
+        type_str = "MOVE";
+        break;
+      case DeltaArchiveManifest_InstallOperation_Type_REPLACE:
+        type_str = "REPLACE";
+        break;
+      case DeltaArchiveManifest_InstallOperation_Type_REPLACE_BZ:
+        type_str = "REPLACE_BZ";
+        break;
+    }
+    LOG(INFO) << i 
+              << (graph[i].valid ? "" : "-INV")
+              << ": " << graph[i].file_name
+              << ": " << type_str;
+    LOG(INFO) << "  src_extents:";
+    DumpExtents(graph[i].op.src_extents(), 4);
+    LOG(INFO) << "  dst_extents:";
+    DumpExtents(graph[i].op.dst_extents(), 4);
+    LOG(INFO) << "  out edges:";
+    DumpOutEdges(graph[i].out_edges);
+  }
+}
+
 }  // namespace graph_utils
 
+bool operator==(const Extent& a, const Extent& b) {
+  return a.start_block() == b.start_block() && a.num_blocks() == b.num_blocks();
+}
+
 }  // namespace chromeos_update_engine
diff --git a/graph_utils.h b/graph_utils.h
index fd602ea..6f7b9a2 100644
--- a/graph_utils.h
+++ b/graph_utils.h
@@ -19,11 +19,43 @@
 // Returns the number of blocks represented by all extents in the edge.
 uint64_t EdgeWeight(const Graph& graph, const Edge& edge);
 
+// These add a read-before dependency from graph[src] -> graph[dst]. If the dep
+// already exists, the block/s is/are added to the existing edge.
+void AddReadBeforeDep(Vertex* src,
+                      Vertex::Index dst,
+                      uint64_t block);
+void AddReadBeforeDepExtents(Vertex* src,
+                             Vertex::Index dst,
+                             const std::vector<Extent>& extents);
+
+void DropWriteBeforeDeps(Vertex::EdgeMap* edge_map);
+
+// For each node N in graph, drop all edges N->|index|.
+void DropIncomingEdgesTo(Graph* graph, Vertex::Index index);
+
 // block must either be the next block in the last extent or a block
 // in the next extent. This function will not handle inserting block
 // into an arbitrary place in the extents.
 void AppendBlockToExtents(std::vector<Extent>* extents, uint64_t block);
 
+// Get/SetElement are intentionally overloaded so that templated functions
+// can accept either type of collection of Extents.
+Extent GetElement(const std::vector<Extent>& collection, size_t index);
+Extent GetElement(
+    const google::protobuf::RepeatedPtrField<Extent>& collection,
+    size_t index);
+
+template<typename T>
+uint64_t BlocksInExtents(const T& collection) {
+  uint64_t ret = 0;
+  for (size_t i = 0; i < static_cast<size_t>(collection.size()); ++i) {
+    ret += GetElement(collection, i).num_blocks();
+  }
+  return ret;
+}
+
+void DumpGraph(const Graph& graph);
+
 }  // namespace graph_utils
 
 }  // namespace chromeos_update_engine
diff --git a/graph_utils_unittest.cc b/graph_utils_unittest.cc
index d947ddd..cfa2b5c 100644
--- a/graph_utils_unittest.cc
+++ b/graph_utils_unittest.cc
@@ -4,8 +4,11 @@
 
 #include <utility>
 #include <vector>
+
 #include <gtest/gtest.h>
+
 #include "update_engine/graph_utils.h"
+#include "update_engine/extent_ranges.h"
 
 using std::make_pair;
 using std::vector;
@@ -38,4 +41,62 @@
   EXPECT_EQ(4, graph_utils::EdgeWeight(graph, make_pair(0, 1)));
 }
 
+TEST(GraphUtilsTest, BlocksInExtentsTest) {
+  {
+    vector<Extent> extents;
+    EXPECT_EQ(0, graph_utils::BlocksInExtents(extents));
+    extents.push_back(ExtentForRange(0, 1));
+    EXPECT_EQ(1, graph_utils::BlocksInExtents(extents));
+    extents.push_back(ExtentForRange(23, 55));
+    EXPECT_EQ(56, graph_utils::BlocksInExtents(extents));
+    extents.push_back(ExtentForRange(1, 2));
+    EXPECT_EQ(58, graph_utils::BlocksInExtents(extents));
+  }
+  {
+    google::protobuf::RepeatedPtrField<Extent> extents;
+    EXPECT_EQ(0, graph_utils::BlocksInExtents(extents));
+    *extents.Add() = ExtentForRange(0, 1);
+    EXPECT_EQ(1, graph_utils::BlocksInExtents(extents));
+    *extents.Add() = ExtentForRange(23, 55);
+    EXPECT_EQ(56, graph_utils::BlocksInExtents(extents));
+    *extents.Add() = ExtentForRange(1, 2);
+    EXPECT_EQ(58, graph_utils::BlocksInExtents(extents));
+  }
+}
+
+TEST(GraphUtilsTest, DepsTest) {
+  Graph graph(3);
+  
+  graph_utils::AddReadBeforeDep(&graph[0], 1, 3);
+  EXPECT_EQ(1, graph[0].out_edges.size());
+  {
+    Extent& extent = graph[0].out_edges[1].extents[0];
+    EXPECT_EQ(3, extent.start_block());
+    EXPECT_EQ(1, extent.num_blocks());
+  }
+  graph_utils::AddReadBeforeDep(&graph[0], 1, 4);
+  EXPECT_EQ(1, graph[0].out_edges.size());
+  {
+    Extent& extent = graph[0].out_edges[1].extents[0];
+    EXPECT_EQ(3, extent.start_block());
+    EXPECT_EQ(2, extent.num_blocks());
+  }
+  graph_utils::AddReadBeforeDepExtents(&graph[2], 1,
+    vector<Extent>(1, ExtentForRange(5, 2)));
+  EXPECT_EQ(1, graph[2].out_edges.size());
+  {
+    Extent& extent = graph[2].out_edges[1].extents[0];
+    EXPECT_EQ(5, extent.start_block());
+    EXPECT_EQ(2, extent.num_blocks());
+  }
+  // Change most recent edge from read-before to write-before
+  graph[2].out_edges[1].write_extents.swap(graph[2].out_edges[1].extents);
+  graph_utils::DropWriteBeforeDeps(&graph[2].out_edges);
+  EXPECT_EQ(0, graph[2].out_edges.size());
+  
+  EXPECT_EQ(1, graph[0].out_edges.size());
+  graph_utils::DropIncomingEdgesTo(&graph, 1);
+  EXPECT_EQ(0, graph[0].out_edges.size());
+}
+
 }  // namespace chromeos_update_engine