text: /****************************************************************************
   * net/tcp/tcp_wrbuffer.c
   *
   *   Copyright (C) 2007-2009, 2013-2014, 2018 Gregory Nutt. All rights
   *     reserved.
   *   Author: Gregory Nutt <gnutt@nuttx.org>
   *           Jason Jiang  <jasonj@live.cn>
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   * 3. Neither the name NuttX nor the names of its contributors may be
   *    used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
   * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
   * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGE.
   *
   ****************************************************************************/
  
  /****************************************************************************
   * Included Files
   ****************************************************************************/
  
  #include <nuttx/net/netconfig.h>
  
  #if defined(CONFIG_DEBUG_FEATURES) && defined(CONFIG_NET_TCP_WRBUFFER_DEBUG)
  /* Force debug output (from this file only) */
  
  #  undef  CONFIG_DEBUG_NET
  #  define CONFIG_DEBUG_NET 1
  #endif
  
  #include <queue.h>
  #include <string.h>
  #include <assert.h>
  #include <errno.h>
  #include <debug.h>
  
  #include <nuttx/semaphore.h>
  #include <nuttx/net/net.h>
  #include <nuttx/mm/iob.h>
  
  #include "utils/utils.h"
  #include "tcp/tcp.h"
  
  #if defined(CONFIG_NET_TCP) && defined(CONFIG_NET_TCP_WRITE_BUFFERS)
  
  /****************************************************************************
   * Private Types
   ****************************************************************************/
  
  /* Package all globals used by this logic into a structure */
  
  struct wrbuffer_s
  {
    /* The semaphore to protect the buffers */
  
    sem_t sem;
  
    /* This is the list of available write buffers */
  
    sq_queue_t freebuffers;
  
    /* These are the pre-allocated write buffers */
  
    struct tcp_wrbuffer_s buffers[CONFIG_NET_TCP_NWRBCHAINS];
  };
  
  /****************************************************************************
   * Private Data
   ****************************************************************************/
  
  /* This is the state of the global write buffer resource */
  
  static struct wrbuffer_s g_wrbuffer;
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: tcp_wrbuffer_initialize
   *
   * Description:
   *   Initialize the list of free write buffers
   *
   * Assumptions:
   *   Called once early initialization.
   *
   ****************************************************************************/
  
  void tcp_wrbuffer_initialize(void)
  {
    int i;
  
    sq_init(&g_wrbuffer.freebuffers);
  
    for (i = 0; i < CONFIG_NET_TCP_NWRBCHAINS; i++)
      {
        sq_addfirst(&g_wrbuffer.buffers[i].wb_node, &g_wrbuffer.freebuffers);
      }
  
    nxsem_init(&g_wrbuffer.sem, 0, CONFIG_NET_TCP_NWRBCHAINS);
    nxsem_setprotocol(&g_wrbuffer.sem, SEM_PRIO_NONE);
  }
  
  /****************************************************************************
   * Name: tcp_wrbuffer_alloc
   *
   * Description:
   *   Allocate a TCP write buffer by taking a pre-allocated buffer from
   *   the free list.  This function is called from TCP logic when a buffer
   *   of TCP data is about to sent
   *
   * Input Parameters:
   *   None
   *
   * Assumptions:
   *   Called from user logic with the network locked.
   *
   ****************************************************************************/
  
  FAR struct tcp_wrbuffer_s *tcp_wrbuffer_alloc(void)
  {
    FAR struct tcp_wrbuffer_s *wrb;
  
    /* We need to allocate two things:  (1) A write buffer structure and (2)
     * at least one I/O buffer to start the chain.
     *
     * Allocate the write buffer structure first then the IOB.  In order to
     * avoid deadlocks, we will need to free the IOB first, then the write
     * buffer
     */
  
    net_lockedwait_uninterruptible(&g_wrbuffer.sem);
  
    /* Now, we are guaranteed to have a write buffer structure reserved
     * for us in the free list.
     */
  
    wrb = (FAR struct tcp_wrbuffer_s *)sq_remfirst(&g_wrbuffer.freebuffers);
    DEBUGASSERT(wrb);
    memset(wrb, 0, sizeof(struct tcp_wrbuffer_s));
  
    /* Now get the first I/O buffer for the write buffer structure */
  
    wrb->wb_iob = net_ioballoc(false, IOBUSER_NET_TCP_WRITEBUFFER);
  
    /* Did we get an IOB?  We should always get one except under some really
     * weird error conditions.
     */
  
    if (wrb->wb_iob == NULL)
      {
        nerr("ERROR: Failed to allocate I/O buffer\n");
        tcp_wrbuffer_release(wrb);
        return NULL;
      }
  
    return wrb;
  }
  
  /****************************************************************************
   * Name: tcp_wrbuffer_tryalloc
   *
   * Description:
   *   Try to allocate a TCP write buffer by taking a pre-allocated buffer from
   *   the free list.  This function is called from TCP logic when a buffer
   *   of TCP data is about to be sent on a non-blocking socket. Returns
   *   immediately if the allocation failed.
   *
   * Input parameters:
   *   None
   *
   * Assumptions:
   *   Called from user logic with the network locked. Will return if no buffer
   *   is available.
   *
   ****************************************************************************/
  
  FAR struct tcp_wrbuffer_s *tcp_wrbuffer_tryalloc(void)
  {
    FAR struct tcp_wrbuffer_s *wrb;
  
    /* We need to allocate two things:  (1) A write buffer structure and (2)
     * at least one I/O buffer to start the chain.
     *
     * Allocate the write buffer structure first then the IOBG.  In order to
     * avoid deadlocks, we will need to free the IOB first, then the write
     * buffer
     */
  
    if (nxsem_trywait(&g_wrbuffer.sem) != OK)
      {
        return NULL;
      }
  
    /* Now, we are guaranteed to have a write buffer structure reserved
     * for us in the free list.
     */
  
    wrb = (FAR struct tcp_wrbuffer_s *)sq_remfirst(&g_wrbuffer.freebuffers);
    DEBUGASSERT(wrb);
    memset(wrb, 0, sizeof(struct tcp_wrbuffer_s));
  
    /* Now get the first I/O buffer for the write buffer structure */
  
    wrb->wb_iob = iob_tryalloc(false, IOBUSER_NET_TCP_WRITEBUFFER);
    if (!wrb->wb_iob)
      {
        nerr("ERROR: Failed to allocate I/O buffer\n");
        tcp_wrbuffer_release(wrb);
        return NULL;
      }
  
    return wrb;
  }
  
  /****************************************************************************
   * Name: tcp_wrbuffer_release
   *
   * Description:
   *   Release a TCP write buffer by returning the buffer to the free list.
   *   This function is called from user logic after it is consumed the
   *   buffered data.
   *
   * Assumptions:
   *   This function must be called with the network locked.
   *
   ****************************************************************************/
  
  void tcp_wrbuffer_release(FAR struct tcp_wrbuffer_s *wrb)
  {
    DEBUGASSERT(wrb != NULL);
  
    /* To avoid deadlocks, we must following this ordering:  Release the I/O
     * buffer chain first, then the write buffer structure.
     */
  
    if (wrb->wb_iob != NULL)
      {
        iob_free_chain(wrb->wb_iob, IOBUSER_NET_TCP_WRITEBUFFER);
      }
  
    /* Then free the write buffer structure */
  
    sq_addlast(&wrb->wb_node, &g_wrbuffer.freebuffers);
    nxsem_post(&g_wrbuffer.sem);
  }
  
  /****************************************************************************
   * Name: tcp_wrbuffer_test
   *
   * Description:
   *   Check if there is room in the write buffer.  Does not reserve any space.
   *
   * Assumptions:
   *   None.
   *
   ****************************************************************************/
  
  int tcp_wrbuffer_test(void)
  {
    int val = 0;
    int ret;
  
    ret = nxsem_getvalue(&g_wrbuffer.sem, &val);
    if (ret >= 0)
      {
        ret = val > 0 ? OK : -ENOSPC;
      }
  
    return ret;
  }
  
  #endif /* CONFIG_NET_TCP && CONFIG_NET_TCP_WRITE_BUFFERS */
  