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diff --git a/src/ceph/src/tools/cephfs/JournalScanner.cc b/src/ceph/src/tools/cephfs/JournalScanner.cc
new file mode 100644
index 0000000..2b88231
--- /dev/null
+++ b/src/ceph/src/tools/cephfs/JournalScanner.cc
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+// -*- mode:c++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- 
+// vim: ts=8 sw=2 smarttab
+/*
+ * ceph - scalable distributed file system
+ *
+ * copyright (c) 2014 john spray <john.spray@inktank.com>
+ *
+ * this is free software; you can redistribute it and/or
+ * modify it under the terms of the gnu lesser general public
+ * license version 2.1, as published by the free software
+ * foundation.  see file copying.
+ */
+
+
+#include "include/rados/librados.hpp"
+#include "mds/JournalPointer.h"
+
+#include "mds/events/ESubtreeMap.h"
+
+#include "JournalScanner.h"
+
+#define dout_context g_ceph_context
+#define dout_subsys ceph_subsys_mds
+
+/**
+ * Read journal header, followed by sequential scan through journal space.
+ *
+ * Return 0 on success, else error code.  Note that success has the special meaning
+ * that we were able to apply our checks, it does *not* mean that the journal is
+ * healthy.
+ */
+int JournalScanner::scan(bool const full)
+{
+  int r = 0;
+
+  r = scan_pointer();
+  if (r < 0) {
+    return r;
+  }
+
+  if (pointer_present) {
+    r = scan_header();
+    if (r < 0) {
+      return r;
+    }
+  }
+
+  if (full && header_present) {
+    r = scan_events();
+    if (r < 0) {
+      return r;
+    }
+  }
+
+  return 0;
+}
+
+
+int JournalScanner::scan_pointer()
+{
+  // Issue read
+  std::string const pointer_oid = obj_name(MDS_INO_LOG_POINTER_OFFSET + rank, 0);
+  bufferlist pointer_bl;
+  int r = io.read(pointer_oid, pointer_bl, INT_MAX, 0);
+  if (r == -ENOENT) {
+    // 'Successfully' discovered the pointer is missing.
+    derr << "Pointer " << pointer_oid << " is absent" << dendl;
+    return 0;
+  } else if (r < 0) {
+    // Error preventing us interrogating pointer
+    derr << "Pointer " << pointer_oid << " is unreadable" << dendl;
+    return r;
+  } else {
+    dout(4) << "Pointer " << pointer_oid << " is readable" << dendl;
+    pointer_present = true;
+
+    JournalPointer jp;
+    try {
+      bufferlist::iterator q = pointer_bl.begin();
+      jp.decode(q);
+    } catch(buffer::error &e) {
+      derr << "Pointer " << pointer_oid << " is corrupt: " << e.what() << dendl;
+      return 0;
+    }
+
+    pointer_valid = true;
+    ino = jp.front;
+    return 0;
+  }
+}
+
+
+int JournalScanner::scan_header()
+{
+  int r;
+
+  bufferlist header_bl;
+  std::string header_name = obj_name(0);
+  dout(4) << "JournalScanner::scan: reading header object '" << header_name << "'" << dendl;
+  r = io.read(header_name, header_bl, INT_MAX, 0);
+  if (r < 0) {
+    derr << "Header " << header_name << " is unreadable" << dendl;
+    return 0;  // "Successfully" found an error
+  } else {
+    header_present = true;
+  }
+
+  bufferlist::iterator header_bl_i = header_bl.begin();
+  header = new Journaler::Header();
+  try
+  {
+    header->decode(header_bl_i);
+  }
+  catch (buffer::error &e)
+  {
+    derr << "Header is corrupt (" << e.what() << ")" << dendl;
+    delete header;
+    header = NULL;
+    return 0;  // "Successfully" found an error
+  }
+
+  if (header->magic != std::string(CEPH_FS_ONDISK_MAGIC)) {
+    derr << "Header is corrupt (bad magic)" << dendl;
+    return 0;  // "Successfully" found an error
+  }
+  if (!((header->trimmed_pos <= header->expire_pos) && (header->expire_pos <= header->write_pos))) {
+    derr << "Header is invalid (inconsistent offsets)" << dendl;
+    return 0;  // "Successfully" found an error
+  }
+  header_valid = true;
+
+  return 0;
+}
+
+
+int JournalScanner::scan_events()
+{
+  uint64_t object_size = g_conf->mds_log_segment_size;
+  if (object_size == 0) {
+    // Default layout object size
+    object_size = file_layout_t::get_default().object_size;
+  }
+
+  uint64_t read_offset = header->expire_pos;
+  dout(10) << std::hex << "Header 0x"
+    << header->trimmed_pos << " 0x"
+    << header->expire_pos << " 0x"
+    << header->write_pos << std::dec << dendl;
+  dout(10) << "Starting journal scan from offset 0x" << std::hex << read_offset << std::dec << dendl;
+
+  // TODO also check for extraneous objects before the trimmed pos or after the write pos,
+  // which would indicate a bogus header.
+
+  bufferlist read_buf;
+  bool gap = false;
+  uint64_t gap_start = -1;
+  for (uint64_t obj_offset = (read_offset / object_size); ; obj_offset++) {
+    uint64_t offset_in_obj = 0;
+    if (obj_offset * object_size < header->expire_pos) {
+      // Skip up to expire_pos from start of the object
+      // (happens for the first object we read)
+      offset_in_obj = header->expire_pos - obj_offset * object_size;
+    }
+
+    // Read this journal segment
+    bufferlist this_object;
+    std::string const oid = obj_name(obj_offset);
+    int r = io.read(oid, this_object, INT_MAX, offset_in_obj);
+
+    // Handle absent journal segments
+    if (r < 0) {
+      if (obj_offset > (header->write_pos / object_size)) {
+        dout(4) << "Reached end of journal objects" << dendl;
+        break;
+      } else {
+        derr << "Missing object " << oid << dendl;
+      }
+
+      objects_missing.push_back(obj_offset);
+      gap = true;
+      gap_start = read_offset;
+      continue;
+    } else {
+      dout(4) << "Read 0x" << std::hex << this_object.length() << std::dec
+              << " bytes from " << oid << " gap=" << gap << dendl;
+      objects_valid.push_back(oid);
+      this_object.copy(0, this_object.length(), read_buf);
+    }
+
+    if (gap) {
+      // No valid data at the current read offset, scan forward until we find something valid looking
+      // or have to drop out to load another object.
+      dout(4) << "Searching for sentinel from 0x" << std::hex << read_offset
+              << ", 0x" << read_buf.length() << std::dec << " bytes available" << dendl;
+
+      do {
+        bufferlist::iterator p = read_buf.begin();
+        uint64_t candidate_sentinel;
+        ::decode(candidate_sentinel, p);
+
+        dout(4) << "Data at 0x" << std::hex << read_offset << " = 0x" << candidate_sentinel << std::dec << dendl;
+
+        if (candidate_sentinel == JournalStream::sentinel) {
+          dout(4) << "Found sentinel at 0x" << std::hex << read_offset << std::dec << dendl;
+          ranges_invalid.push_back(Range(gap_start, read_offset));
+          gap = false;
+          break;
+        } else {
+          // No sentinel, discard this byte
+          read_buf.splice(0, 1);
+          read_offset += 1;
+        }
+      } while (read_buf.length() >= sizeof(JournalStream::sentinel));
+      dout(4) << "read_buf size is " << read_buf.length() << dendl;
+    } else {
+      dout(10) << "Parsing data, 0x" << std::hex << read_buf.length() << std::dec << " bytes available" << dendl;
+      while(true) {
+        // TODO: detect and handle legacy format journals: can do many things
+        // on them but on read errors have to give up instead of searching
+        // for sentinels.
+        JournalStream journal_stream(JOURNAL_FORMAT_RESILIENT);
+        bool readable = false;
+        try {
+          uint64_t need;
+          readable = journal_stream.readable(read_buf, &need);
+        } catch (buffer::error &e) {
+          readable = false;
+          dout(4) << "Invalid container encoding at 0x" << std::hex << read_offset << std::dec << dendl;
+          gap = true;
+          gap_start = read_offset;
+          read_buf.splice(0, 1);
+          read_offset += 1;
+          break;
+        }
+
+        if (!readable) {
+          // Out of data, continue to read next object
+          break;
+        }
+
+        bufferlist le_bl;  //< Serialized LogEvent blob
+        dout(10) << "Attempting decode at 0x" << std::hex << read_offset << std::dec << dendl;
+        // This cannot fail to decode because we pre-checked that a serialized entry
+        // blob would be readable.
+        uint64_t start_ptr = 0;
+        uint64_t consumed = journal_stream.read(read_buf, &le_bl, &start_ptr);
+        dout(10) << "Consumed 0x" << std::hex << consumed << std::dec << " bytes" << dendl;
+        if (start_ptr != read_offset) {
+          derr << "Bad entry start ptr (0x" << std::hex << start_ptr << ") at 0x"
+              << read_offset << std::dec << dendl;
+          gap = true;
+          gap_start = read_offset;
+          // FIXME: given that entry was invalid, should we be skipping over it?
+          // maybe push bytes back onto start of read_buf and just advance one byte
+          // to start scanning instead.  e.g. if a bogus size value is found it can
+          // cause us to consume and thus skip a bunch of following valid events.
+          read_offset += consumed;
+          break;
+        }
+
+        LogEvent *le = LogEvent::decode(le_bl);
+
+        if (le) {
+          dout(10) << "Valid entry at 0x" << std::hex << read_offset << std::dec << dendl;
+
+          if (le->get_type() == EVENT_SUBTREEMAP
+              || le->get_type() == EVENT_SUBTREEMAP_TEST) {
+            ESubtreeMap *sle = dynamic_cast<ESubtreeMap*>(le);
+            if (sle->expire_pos > read_offset) {
+              errors.insert(std::make_pair(
+                    read_offset, EventError(
+                      -ERANGE,
+                      "ESubtreeMap has expire_pos ahead of its own position")));
+            }
+          }
+
+          if (filter.apply(read_offset, *le)) {
+            events[read_offset] = EventRecord(le, consumed);
+          } else {
+            delete le;
+          }
+          events_valid.push_back(read_offset);
+          read_offset += consumed;
+        } else {
+          dout(10) << "Invalid entry at 0x" << std::hex << read_offset << std::dec << dendl;
+          gap = true;
+          gap_start = read_offset;
+          read_offset += consumed;
+        }
+      }
+    }
+  }
+
+  if (gap) {
+    // Ended on a gap, assume it ran to end
+    ranges_invalid.push_back(Range(gap_start, -1));
+  }
+
+  dout(4) << "Scanned objects, " << objects_missing.size() << " missing, " << objects_valid.size() << " valid" << dendl;
+  dout(4) << "Events scanned, " << ranges_invalid.size() << " gaps" << dendl;
+  dout(4) << "Found " << events_valid.size() << " valid events" << dendl;
+  dout(4) << "Selected " << events.size() << " events events for processing" << dendl;
+
+  return 0;
+}
+
+
+JournalScanner::~JournalScanner()
+{
+  if (header) {
+    delete header;
+    header = NULL;
+  }
+  dout(4) << events.size() << " events" << dendl;
+  for (EventMap::iterator i = events.begin(); i != events.end(); ++i) {
+    delete i->second.log_event;
+  }
+  events.clear();
+}
+
+
+/**
+ * Whether the journal data looks valid and replayable
+ */
+bool JournalScanner::is_healthy() const
+{
+  return (pointer_present && pointer_valid
+      && header_present && header_valid
+      && ranges_invalid.empty()
+      && objects_missing.empty());
+}
+
+
+/**
+ * Whether the journal data can be read from RADOS
+ */
+bool JournalScanner::is_readable() const
+{
+  return (header_present && header_valid && objects_missing.empty());
+}
+
+
+/**
+ * Calculate the object name for a given offset
+ */
+std::string JournalScanner::obj_name(inodeno_t ino, uint64_t offset) const
+{
+  char name[60];
+  snprintf(name, sizeof(name), "%llx.%08llx",
+      (unsigned long long)(ino),
+      (unsigned long long)offset);
+  return std::string(name);
+}
+
+
+std::string JournalScanner::obj_name(uint64_t offset) const
+{
+  return obj_name(ino, offset);
+}
+
+
+/*
+ * Write a human readable summary of the journal health
+ */
+void JournalScanner::report(std::ostream &out) const
+{
+  out << "Overall journal integrity: " << (is_healthy() ? "OK" : "DAMAGED") << std::endl;
+
+  if (!pointer_present) {
+    out << "Pointer not found" << std::endl;
+  } else if (!pointer_valid) {
+    out << "Pointer could not be decoded" << std::endl;
+  }
+
+  if (!header_present) {
+    out << "Header not found" << std::endl;
+  } else if (!header_valid) {
+    out << "Header could not be decoded" << std::endl;
+  }
+
+  if (objects_missing.size()) {
+    out << "Objects missing:" << std::endl;
+    for (std::vector<uint64_t>::const_iterator om = objects_missing.begin();
+         om != objects_missing.end(); ++om) {
+      out << "  0x" << std::hex << *om << std::dec << std::endl;
+    }
+  }
+
+  if (ranges_invalid.size()) {
+    out << "Corrupt regions:" << std::endl;
+    for (std::vector<Range>::const_iterator r = ranges_invalid.begin();
+         r != ranges_invalid.end(); ++r) {
+      out << "  0x" << std::hex << r->first << "-" << r->second << std::dec << std::endl;
+    }
+  }
+}
+