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+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2015 Red Hat
+ *
+ * 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 STRAY_MANAGER_H
+#define STRAY_MANAGER_H
+
+#include "include/elist.h"
+#include <list>
+#include "mds/PurgeQueue.h"
+
+class MDSRank;
+class PerfCounters;
+class CInode;
+class CDentry;
+
+class StrayManager
+{
+  protected:
+  // Has passed through eval_stray and still has refs
+  elist<CDentry*> delayed_eval_stray;
+
+  // strays that have been trimmed from cache
+  std::set<std::string> trimmed_strays;
+
+  // Global references for doing I/O
+  MDSRank *mds;
+  PerfCounters *logger;
+
+  bool started;
+
+  // Stray dentries for this rank (including those not in cache)
+  uint64_t num_strays;
+
+  // Stray dentries
+  uint64_t num_strays_delayed;
+
+  // Entries that have entered enqueue() but not been persistently
+  // recorded by PurgeQueue yet
+  uint64_t num_strays_enqueuing;
+
+  PurgeQueue &purge_queue;
+
+  void truncate(CDentry *dn);
+
+  /**
+   * Purge a dentry from a stray directory.  This function
+   * is called once eval_stray is satisfied and StrayManager
+   * throttling is also satisfied.  There is no going back
+   * at this stage!
+   */
+  void purge(CDentry *dn);
+
+  /**
+   * Completion handler for a Filer::purge on a stray inode.
+   */
+  void _purge_stray_purged(CDentry *dn, bool only_head);
+
+  void _purge_stray_logged(CDentry *dn, version_t pdv, LogSegment *ls);
+
+  /**
+   * Callback: we have logged the update to an inode's metadata
+   * reflecting it's newly-zeroed length.
+   */
+  void _truncate_stray_logged(CDentry *dn, LogSegment *ls);
+
+  friend class StrayManagerIOContext;
+  friend class StrayManagerLogContext;
+  friend class StrayManagerContext;
+
+  friend class C_StraysFetched;
+  friend class C_OpenSnapParents;
+  friend class C_PurgeStrayLogged;
+  friend class C_TruncateStrayLogged;
+  friend class C_IO_PurgeStrayPurged;
+
+
+  // Call this on a dentry that has been identified as
+  // eligible for purging.  It will be passed on to PurgeQueue.
+  void enqueue(CDentry *dn, bool trunc);
+
+  // Final part of enqueue() which we may have to retry
+  // after opening snap parents.
+  void _enqueue(CDentry *dn, bool trunc);
+
+
+  /**
+   * When hard links exist to an inode whose primary dentry
+   * is unlinked, the inode gets a stray primary dentry.
+   *
+   * We may later "reintegrate" the inode into a remaining
+   * non-stray dentry (one of what was previously a remote
+   * dentry) by issuing a rename from the stray to the other
+   * dentry.
+   */
+  void reintegrate_stray(CDentry *dn, CDentry *rlink);
+
+  /**
+   * Evaluate a stray dentry for purging or reintegration.
+   *
+   * purging: If the inode has no linkage, and no more references, then
+   *          we may decide to purge it.
+   *
+   * reintegration: If the inode still has linkage, then it means someone else
+   *                (a hard link) is still referring to it, and we should
+   *                think about reintegrating that inode into the remote dentry.
+   *
+   * @returns true if the dentry will be purged (caller should never
+   *          take more refs after this happens), else false.
+   */
+  bool _eval_stray(CDentry *dn);
+
+  void _eval_stray_remote(CDentry *stray_dn, CDentry *remote_dn);
+
+  // My public interface is for consumption by MDCache
+  public:
+  explicit StrayManager(MDSRank *mds, PurgeQueue &purge_queue_);
+  void set_logger(PerfCounters *l) {logger = l;}
+  void activate();
+
+  bool eval_stray(CDentry *dn);
+
+  void set_num_strays(uint64_t num);
+  uint64_t get_num_strays() const { return num_strays; }
+
+  /**
+   * Queue dentry for later evaluation. (evaluate it while not in the
+   * middle of another metadata operation)
+   */
+  void queue_delayed(CDentry *dn);
+
+  /**
+   * Eval strays in the delayed_eval_stray list
+   */
+  void advance_delayed();
+
+  /**
+   * Remote dentry potentially points to a stray. When it is touched,
+   * call in here to evaluate it for migration (move a stray residing
+   * on another MDS to this MDS) or reintegration (move a stray dentry's
+   * inode into a non-stray hardlink dentry and clean up the stray).
+   *
+   * @param stray_dn a stray dentry whose inode has been referenced
+   *                 by a remote dentry
+   * @param remote_dn (optional) which remote dentry was touched
+   *                  in an operation that led us here: this is used
+   *                  as a hint for which remote to reintegrate into
+   *                  if there are multiple remotes.
+   */
+  void eval_remote(CDentry *remote_dn);
+
+  /**
+   * Given a dentry within one of my stray directories,
+   * send it off to a stray directory in another MDS.
+   *
+   * This is for use:
+   *  * Case A: when shutting down a rank, we migrate strays
+   *    away from ourselves rather than waiting for purge
+   *  * Case B: when a client request has a trace that refers to
+   *    a stray inode on another MDS, we migrate that inode from
+   *    there to here, in order that we can later re-integrate it
+   *    here.
+   *
+   * In case B, the receiver should be calling into eval_stray
+   * on completion of mv (i.e. inode put), resulting in a subsequent
+   * reintegration.
+   */
+  void migrate_stray(CDentry *dn, mds_rank_t dest);
+
+  /**
+   * Update stats to reflect a newly created stray dentry.  Needed
+   * because stats on strays live here, but creation happens
+   * in Server or MDCache.  For our purposes "creation" includes
+   * loading a stray from a dirfrag and migrating a stray from
+   * another MDS, in addition to creations per-se.
+   */
+  void notify_stray_created();
+
+  /**
+   * Update stats to reflect a removed stray dentry.  Needed because
+   * stats on strays live here, but removal happens in Server or
+   * MDCache.  Also includes migration (rename) of strays from
+   * this MDS to another MDS.
+   */
+  void notify_stray_removed();
+};
+
+#endif  // STRAY_MANAGER_H