/*
   * snapshot.c    Ceph snapshot context utility routines (part of libceph)
   *
   * Copyright (C) 2013 Inktank Storage, Inc.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * version 2 as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
   * 02110-1301, USA.
   */
  
  #include <stddef.h>
  
  #include <linux/types.h>
  #include <linux/export.h>
  #include <linux/ceph/libceph.h>
  
  /*
   * Ceph snapshot contexts are reference counted objects, and the
   * returned structure holds a single reference.  Acquire additional
   * references with ceph_get_snap_context(), and release them with
   * ceph_put_snap_context().  When the reference count reaches zero
   * the entire structure is freed.
   */
  
  /*
   * Create a new ceph snapshot context large enough to hold the
   * indicated number of snapshot ids (which can be 0).  Caller has
   * to fill in snapc->seq and snapc->snaps[0..snap_count-1].
   *
   * Returns a null pointer if an error occurs.
   */
  struct ceph_snap_context *ceph_create_snap_context(u32 snap_count,
  						gfp_t gfp_flags)
  {
  	struct ceph_snap_context *snapc;
  	size_t size;
  
  	size = sizeof (struct ceph_snap_context);
  	size += snap_count * sizeof (snapc->snaps[0]);
  	snapc = kzalloc(size, gfp_flags);
  	if (!snapc)
  		return NULL;
  
  	atomic_set(&snapc->nref, 1);
  	snapc->num_snaps = snap_count;
  
  	return snapc;
  }
  EXPORT_SYMBOL(ceph_create_snap_context);
  
  struct ceph_snap_context *ceph_get_snap_context(struct ceph_snap_context *sc)
  {
  	if (sc)
  		atomic_inc(&sc->nref);
  	return sc;
  }
  EXPORT_SYMBOL(ceph_get_snap_context);
  
  void ceph_put_snap_context(struct ceph_snap_context *sc)
  {
  	if (!sc)
  		return;
  	if (atomic_dec_and_test(&sc->nref)) {
  		/*printk(" deleting snap_context %p
  ", sc);*/
  		kfree(sc);
  	}
  }
  EXPORT_SYMBOL(ceph_put_snap_context);