ceph/src/cls/refcount/cls_refcount_client.h

   1 #ifndef CEPH_CLS_REFCOUNT_CLIENT_H
   2 #define CEPH_CLS_REFCOUNT_CLIENT_H
   3
   4 #include "include/types.h"
   5 #include "include/rados/librados.hpp"
   6
   7 /*
   8  * refcount objclass
   9  *
  10  * The refcount objclass implements a refcounting scheme that allows having multiple references
  11  * to a single rados object. The canonical way to use it is to add a reference and to remove a
  12  * reference using a specific tag. This way we ensure that refcounting operations are idempotent,
  13  * that is, a single client can only increase/decrease the refcount once using a single tag, so
  14  * any replay of operations (implicit or explicit) is possible.
  15  *
  16  * So, the regular usage would be to create an object, to increase the refcount. Then, when
  17  * wanting to have another reference to it, increase the refcount using a different tag. When
  18  * removing a reference it is required to drop the refcount (using the same tag that was used
  19  * for that reference). When the refcount drops to zero, the object is removed automaticfally.
  20  *
  21  * In order to maintain backwards compatibility with objects that were created without having
  22  * their refcount increased, the implicit_ref was added. Any object that was created without
  23  * having it's refcount increased (explicitly) is having an implicit refcount of 1. Since
  24  * we don't have a tag for this refcount, we consider this tag as a wildcard. So if the refcount
  25  * is being decreased by an unknown tag and we still have one wildcard tag, we'll accept it
  26  * as the relevant tag, and the refcount will be decreased.
  27  */
  28
  29 void cls_refcount_get(librados::ObjectWriteOperation& op, const string& tag, bool implicit_ref = false);
  30 void cls_refcount_put(librados::ObjectWriteOperation& op, const string& tag, bool implicit_ref = false);
  31 void cls_refcount_set(librados::ObjectWriteOperation& op, list<string>& refs);
  32 int cls_refcount_read(librados::IoCtx& io_ctx, string& oid, list<string> *refs, bool implicit_ref = false);
  33
  34 #endif