incubator-nuttx/mm/iob/iob_peek_queue.c

/****************************************************************************
 * mm/iob/iob_peek_queue.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <debug.h>

#include <nuttx/mm/iob.h>

#include "iob.h"

#if CONFIG_IOB_NCHAINS > 0

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

#ifndef NULL
#  define NULL ((FAR void *)0)
#endif

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: iob_peek_queue
 *
 * Description:
 *   Return a reference to the I/O buffer chain at the head of a queue. This
 *   is similar to iob_remove_queue except that the I/O buffer chain is in
 *   place at the head of the queue.  The I/O buffer chain may safely be
 *   modified by the caller but must be removed from the queue before it can
 *   be freed.
 *
 * Returned Value:
 *   Returns a reference to the I/O buffer chain at the head of the queue.
 *
 ****************************************************************************/

FAR struct iob_s *iob_peek_queue(FAR struct iob_queue_s *iobq)
{
  FAR struct iob_qentry_s *qentry;
  FAR struct iob_s *iob = NULL;

  /* Peek at the I/O buffer chain container at the head of the queue */

  qentry = iobq->qh_head;
  if (qentry)
    {
      /* Return the I/O buffer chain from the container */

      iob = qentry->qe_head;
    }

  return iob;
}

#endif /* CONFIG_IOB_NCHAINS > 0 */