From d60ac6ffaac11851042a5978ac10f52293a50b50 Mon Sep 17 00:00:00 2001
From: Michael Vrable <mvrable@cs.ucsd.edu>
Date: Thu, 3 May 2007 14:23:21 -0700
Subject: [PATCH] Partial support for tracker inter-object references.

---
 scandir.cc  |  1 +
 tarstore.cc | 28 +++++++++++++++++++++++++++-
 tarstore.h  | 20 ++++++++++++++++----
 3 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/scandir.cc b/scandir.cc
index 20f8351..1616187 100644
--- a/scandir.cc
+++ b/scandir.cc
@@ -132,6 +132,7 @@ void scanfile(const string& path, ostream &metadata)
     struct stat stat_buf;
     char *buf;
     ssize_t len;
+    list<string> refs;
 
     // Set to true if the item is a directory and we should recursively scan
     bool recurse = false;
diff --git a/tarstore.cc b/tarstore.cc
index b90426b..5133c66 100644
--- a/tarstore.cc
+++ b/tarstore.cc
@@ -14,13 +14,19 @@
 #include <time.h>
 #include <uuid/uuid.h>
 
+#include <list>
+#include <set>
 #include <string>
 #include <iostream>
 
 #include "tarstore.h"
 
+using std::list;
+using std::set;
 using std::string;
 
+list<string> TarSegmentStore::norefs;
+
 Tarfile::Tarfile(const string &path, const string &segment)
     : size(0),
       segment_name(segment)
@@ -99,7 +105,8 @@ void Tarfile::internal_write_object(const string &path,
 static const size_t SEGMENT_SIZE = 4 * 1024 * 1024;
 
 string TarSegmentStore::write_object(const char *data, size_t len, const
-                                     std::string &group)
+                                     std::string &group,
+                                     const std::list<std::string> &refs)
 {
     struct segment_info *segment;
 
@@ -133,6 +140,12 @@ string TarSegmentStore::write_object(const char *data, size_t len, const
 
     string full_name = segment->name + "/" + id_buf;
 
+    // Store any dependencies this object has on other segments, so they can be
+    // written when the segment is closed.
+    for (list<string>::const_iterator i = refs.begin(); i != refs.end(); ++i) {
+        segment->refs.insert(*i);
+    }
+
     // If this segment meets or exceeds the size target, close it so that
     // future objects will go into a new segment.
     if (segment->file->size_estimate() >= SEGMENT_SIZE)
@@ -153,7 +166,20 @@ void TarSegmentStore::close_segment(const string &group)
     fprintf(stderr, "Closing segment group %s (%s)\n",
             group.c_str(), segment->name.c_str());
 
+    string reflist;
+    for (set<string>::iterator i = segment->refs.begin();
+         i != segment->refs.end(); ++i) {
+        reflist += *i + "\n";
+    }
+    segment->file->internal_write_object(segment->name + "/references",
+                                         reflist.data(), reflist.size());
+
     delete segment->file;
     segments.erase(segments.find(group));
     delete segment;
 }
+
+string TarSegmentStore::object_reference_to_segment(const string &object)
+{
+    return object;
+}
diff --git a/tarstore.h b/tarstore.h
index ebf4061..a657ec9 100644
--- a/tarstore.h
+++ b/tarstore.h
@@ -12,6 +12,8 @@
 #include <stdint.h>
 #include <libtar.h>
 
+#include <list>
+#include <set>
 #include <string>
 #include <iostream>
 #include <sstream>
@@ -31,10 +33,10 @@ public:
     // Return an estimate of the size of the file.
     size_t size_estimate() { return size; }
 
-private:
     void internal_write_object(const std::string &path,
                                const char *data, size_t len);
 
+private:
     size_t size;
     std::string segment_name;
     std::ostringstream checksums;
@@ -52,7 +54,8 @@ public:
     // used to control object placement; objects with different group
     // parameters are kept in separate segments.
     std::string write_object(const char *data, size_t len,
-                             const std::string &group = "");
+                             const std::string &group = "",
+                             const std::list<std::string> &refs = norefs);
 
     // Ensure all segments have been fully written.
     void sync();
@@ -60,15 +63,24 @@ public:
 private:
     struct segment_info {
         Tarfile *file;
-        std::string name;       // UUID
-        int count;              // Objects written to this segment
+        std::string name;           // UUID
+        std::set<std::string> refs; // Other segments this one refers to
+        int count;                  // Objects written to this segment
     };
 
     std::string path;
     std::map<std::string, struct segment_info *> segments;
 
+    // An empty list which can be used as an argument to write_object to
+    // indicate that this object depends on no others.
+    static std::list<std::string> norefs;
+
     // Ensure that all segments in the given group have been fully written.
     void close_segment(const std::string &group);
+
+    // Parse an object reference string and return just the segment name
+    // portion.
+    std::string object_reference_to_segment(const std::string &object);
 };
 
 #endif // _LBS_TARSTORE_H
-- 
2.20.1