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diff --git a/src/mds/DamageTable.h b/src/mds/DamageTable.h
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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) 2004-2006 Sage Weil <sage@newdream.net>
+ *
+ * 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.
+ *
+ */
+
+
+#ifndef DAMAGE_TABLE_H_
+#define DAMAGE_TABLE_H_
+
+#include <string_view>
+
+#include "mdstypes.h"
+#include "include/random.h"
+
+class CDir;
+
+typedef uint64_t damage_entry_id_t;
+
+typedef enum
+{
+  DAMAGE_ENTRY_DIRFRAG,
+  DAMAGE_ENTRY_DENTRY,
+  DAMAGE_ENTRY_BACKTRACE
+
+} damage_entry_type_t;
+
+class DamageEntry
+{
+  public:
+  damage_entry_id_t id;
+  utime_t reported_at;
+
+  // path is optional, advisory.  Used to give the admin an idea of what
+  // part of his tree the damage affects.
+  std::string path;
+
+  DamageEntry()
+  {
+    id = ceph::util::generate_random_number<damage_entry_id_t>(0, 0xffffffff);
+    reported_at = ceph_clock_now();
+  }
+
+  virtual damage_entry_type_t get_type() const = 0;
+
+  virtual ~DamageEntry();
+
+  virtual void dump(Formatter *f) const = 0;
+};
+
+
+typedef std::shared_ptr<DamageEntry> DamageEntryRef;
+
+
+class DirFragIdent
+{
+  public:
+  inodeno_t ino;
+  frag_t frag;
+
+  bool operator<(const DirFragIdent &rhs) const
+  {
+    if (ino == rhs.ino) {
+      return frag < rhs.frag;
+    } else {
+      return ino < rhs.ino;
+    }
+  }
+
+  DirFragIdent(inodeno_t ino_, frag_t frag_)
+    : ino(ino_), frag(frag_)
+  {}
+};
+
+class DentryIdent
+{
+  public:
+  std::string dname;
+  snapid_t snap_id;
+
+  bool operator<(const DentryIdent &rhs) const
+  {
+    if (dname == rhs.dname) {
+      return snap_id < rhs.snap_id;
+    } else {
+      return dname < rhs.dname;
+    }
+  }
+
+  DentryIdent(std::string_view dname_, snapid_t snap_id_)
+    : dname(dname_), snap_id(snap_id_)
+  {}
+};
+
+/**
+ * Registry of in-RADOS metadata damage identified
+ * during forward scrub or during normal fetches.
+ *
+ * Used to indicate damage to the administrator, and
+ * to cache known-bad paths so that we don't hit them
+ * repeatedly.
+ *
+ * Callers notifying damage must check return code; if
+ * an fatal condition is indicated then they should mark the MDS
+ * rank damaged.
+ *
+ * An artificial limit on the number of damage entries
+ * is imposed to avoid this structure growing indefinitely.  If
+ * a notification causes the limit to be exceeded, the fatal
+ * condition will be indicated in the return code and the MDS
+ * rank should be marked damaged.
+ *
+ * Protected by MDS::mds_lock
+ */
+class DamageTable
+{
+protected:
+
+  // Map of all dirfrags reported damaged
+  std::map<DirFragIdent, DamageEntryRef> dirfrags;
+
+  // Store dentries in a map per dirfrag, so that we can
+  // readily look up all the bad dentries in a particular
+  // dirfrag
+  std::map<DirFragIdent, std::map<DentryIdent, DamageEntryRef> > dentries;
+
+  // Map of all inodes which could not be resolved remotely
+  // (i.e. have probably/possibly missing backtraces)
+  std::map<inodeno_t, DamageEntryRef> remotes;
+
+  // All damage, by ID.  This is a secondary index
+  // to the dirfrag, dentry, remote maps.  It exists
+  // to enable external tools to unambiguously operate
+  // on particular entries.
+  std::map<damage_entry_id_t, DamageEntryRef> by_id;
+
+  // I need to know my MDS rank so that I can check if
+  // metadata items are part of my mydir.
+  const mds_rank_t rank;
+
+  bool oversized() const;
+
+public:
+
+  /**
+   * Return true if no damage entries exist
+   */
+  bool empty() const
+  {
+    return by_id.empty();
+  }
+
+  /**
+   * Indicate that a dirfrag cannot be loaded.
+   *
+   * @return true if fatal
+   */
+  bool notify_dirfrag(inodeno_t ino, frag_t frag, std::string_view path);
+
+  /**
+   * Indicate that a particular dentry cannot be loaded.
+   *
+   * @return true if fatal
+   */
+  bool notify_dentry(
+    inodeno_t ino, frag_t frag,
+    snapid_t snap_id, std::string_view dname, std::string_view path);
+
+  /**
+   * Indicate that a particular Inode could not be loaded by number
+   */
+  bool notify_remote_damaged(
+      inodeno_t ino, std::string_view path);
+
+  bool is_dentry_damaged(
+      const CDir *dir_frag,
+      std::string_view dname,
+      const snapid_t snap_id) const;
+
+  bool is_dirfrag_damaged(
+      const CDir *dir_frag) const;
+
+  bool is_remote_damaged(
+      const inodeno_t ino) const;
+
+
+  explicit DamageTable(const mds_rank_t rank_)
+    : rank(rank_)
+  {
+    ceph_assert(rank_ != MDS_RANK_NONE);
+  }
+
+  void dump(Formatter *f) const;
+
+  void erase(damage_entry_id_t damage_id);
+};
+
+#endif // DAMAGE_TABLE_H_
+