p->flags == PBUF_FLAG_REF || p->flags == PBUF_FLAG_POOL);

  count = 0;
  /* Since decrementing ref cannot be guaranteed to be a single machine operation
   * we must protect it. Also, the later test of ref must be protected.
   */
//丁一修改
#if SYS_LIGHTWEIGHT_PROT
  SYS_ARCH_PROTECT(old_level);
#else /* SYS_LIGHTWEIGHT_PROT */  
  sys_sem_wait(pbuf_pool_free_sem);
#endif /* SYS_LIGHTWEIGHT_PROT */  
//原本
//  SYS_ARCH_PROTECT(old_level);



  /* de-allocate all consecutive pbufs from the head of the chain that
   * obtain a zero reference count */
  while (p != NULL) {
    /* all pbufs in a chain are referenced at least once */
    LWIP_ASSERT("pbuf_free: p->ref > 0", p->ref > 0);
    p->ref--;
    /* this pbuf is no longer referenced to? */
    if (p->ref == 0) {
      /* remember next pbuf in chain for next iteration */
      q = p->next;
      /* is this a pbuf from the pool? */
      if (p->flags == PBUF_FLAG_POOL) {
        p->len = p->tot_len = PBUF_POOL_BUFSIZE;
        p->payload = (void *)((u8_t *)p + sizeof(struct pbuf));
        PBUF_POOL_FREE(p);
      /* a RAM/ROM referencing pbuf */
      } else if (p->flags == PBUF_FLAG_ROM || p->flags == PBUF_FLAG_REF) {
        memp_freep(MEMP_PBUF, p);
      /* pbuf with data */
      } else {
        mem_free(p);
      }
      count++;
      /* proceed to next pbuf */
      p = q;
    /* p->ref > 0, this pbuf is still referenced to */
    /* (so the remaining pbufs in chain as well)    */
    } else {
      /* stop walking through chain */
      p = NULL;
    }
  }
  
 //丁一修改  
#if SYS_LIGHTWEIGHT_PROT
  SYS_ARCH_UNPROTECT(old_level);
#else /* SYS_LIGHTWEIGHT_PROT */
  sys_sem_signal(pbuf_pool_free_sem);
#endif /* SYS_LIGHTWEIGHT_PROT */  
//原本  
//  SYS_ARCH_UNPROTECT(old_level);  

  pbuf_refresh();
  PERF_STOP("pbuf_free");
  /* return number of de-allocated pbufs */
  return count;
}

/**
 * Count number of pbufs in a chain
 *
 * @param p first pbuf of chain
 * @return the number of pbufs in a chain
 */

u8_t
pbuf_clen(struct pbuf *p)
{
  u8_t len;

  len = 0;  
  while (p != NULL) {
    ++len;
    p = p->next;
  }
  return len;
}
/**
 *
 * Increment the reference count of the pbuf.
 *
 * @param p pbuf to increase reference counter of
 *
 */
void
pbuf_ref(struct pbuf *p)
{
//丁一修改
#if SYS_LIGHTWEIGHT_PROT
  SYS_ARCH_DECL_PROTECT(old_level);
#endif /* SYS_LIGHTWEIGHT_PROT */  
//原本
//  SYS_ARCH_DECL_PROTECT(old_level);
  /* pbuf given? */  
  if (p != NULL) {
//丁一修改
#if SYS_LIGHTWEIGHT_PROT
  SYS_ARCH_PROTECT(old_level);
#else /* SYS_LIGHTWEIGHT_PROT */  
  sys_sem_wait(pbuf_pool_free_sem);
#endif /* SYS_LIGHTWEIGHT_PROT */  
//原本
//    SYS_ARCH_PROTECT(old_level);
    ++(p->ref);

//丁一修改  
#if SYS_LIGHTWEIGHT_PROT
  SYS_ARCH_UNPROTECT(old_level);
#else /* SYS_LIGHTWEIGHT_PROT */
  sys_sem_signal(pbuf_pool_free_sem);
#endif /* SYS_LIGHTWEIGHT_PROT */  
//原本  
//  SYS_ARCH_UNPROTECT(old_level);  

  }
}

/**
 *
 * Increment the reference count of all pbufs in a chain.
 *
 * @param p first pbuf of chain
 *
 */
void
pbuf_ref_chain(struct pbuf *p)
{
//丁一修改
#if SYS_LIGHTWEIGHT_PROT
  SYS_ARCH_DECL_PROTECT(old_level);
  SYS_ARCH_PROTECT(old_level);
#else /* SYS_LIGHTWEIGHT_PROT */  
  sys_sem_wait(pbuf_pool_free_sem);
#endif /* SYS_LIGHTWEIGHT_PROT */  
//原本
//  SYS_ARCH_DECL_PROTECT(old_level);
//  SYS_ARCH_PROTECT(old_level);
    
  while (p != NULL) {
    ++p->ref;
    p = p->next;
  }
  
//丁一修改  
#if SYS_LIGHTWEIGHT_PROT
  SYS_ARCH_UNPROTECT(old_level);
#else /* SYS_LIGHTWEIGHT_PROT */
  sys_sem_signal(pbuf_pool_free_sem);
#endif /* SYS_LIGHTWEIGHT_PROT */  
//原本  
//  SYS_ARCH_UNPROTECT(old_level);  

}


/**
 *
 * Link two pbufs (or chains) together.
 *
 * @param h head pbuf (chain)
 * @param t tail pbuf (chain)
 * 
 * The ->tot_len field of the first pbuf (h) is adjusted.
 */
void
pbuf_chain(struct pbuf *h, struct pbuf *t)
{
  struct pbuf *p;

  LWIP_ASSERT("h != NULL", h != NULL);
  LWIP_ASSERT("t != NULL", t != NULL);
  
  /* proceed to last pbuf of chain */
  for (p = h; p->next != NULL; p = p->next) {
    /* add total length of second chain to all totals of first chain */
    p->tot_len += t->tot_len;
  }
  /* p is last pbuf of first h chain */
  /* add total length of second chain to last pbuf total of first chain */
  p->tot_len += t->tot_len;
  /* chain last pbuf of h chain (p) with first of tail (t) */
  p->next = t;
  /* t is now referenced to one more time */
  pbuf_ref(t);
  DEBUGF(PBUF_DEBUG | DBG_FRESH | 2, ("pbuf_chain: referencing tail %p\n", (void *) t));
}

/**
 * Dechains the first pbuf from its succeeding pbufs in the chain.
 *
 * Makes p->tot_len field equal to p->len.
 * @param p pbuf to dechain
 * @return remainder of the pbuf chain, or NULL if it was de-allocated.
 */
struct pbuf *
pbuf_dechain(struct pbuf *p)
{
  struct pbuf *q;
  u8_t tail_gone = 1;
  /* tail */  
  q = p->next;
  /* pbuf has successor in chain? */
  if (q != NULL) {
    /* assert tot_len invariant: (p->tot_len == p->len + (p->next? p->next->tot_len: 0) */
    LWIP_ASSERT("p->tot_len == p->len + q->tot_len", q->tot_len == p->tot_len - p->len);
    /* enforce invariant if assertion is disabled */
    q->tot_len = p->tot_len - p->len;
    /* decouple pbuf from remainder */
    p->next = NULL;
    /* total length of pbuf p is its own length only */
    p->tot_len = p->len;
    /* q is no longer referenced by p, free it */
    DEBUGF(PBUF_DEBUG | DBG_STATE, ("pbuf_dechain: unreferencing %p\n", (void *) q));
    tail_gone = pbuf_free(q);
    /* return remaining tail or NULL if deallocated */
  }
  /* assert tot_len invariant: (p->tot_len == p->len + (p->next? p->next->tot_len: 0) */
  LWIP_ASSERT("p->tot_len == p->len", p->tot_len == p->len);
  return (tail_gone > 0? NULL: q);
}

/**
 *
 * Create PBUF_POOL (or PBUF_RAM) copies of PBUF_REF pbufs.
 *
 * Go through a pbuf chain and replace any PBUF_REF buffers
 * with PBUF_POOL (or PBUF_RAM) pbufs, each taking a copy of
 * the referenced data.
 *
 * @note You MUST explicitly use p = pbuf_take(p);
 * The pbuf you give as argument, may have been replaced
 * by pbuf_take()!
 *
 * @note Any replaced pbufs will be freed through pbuf_free().
 *
 * Used to queue packets on behalf of the lwIP stack, such as
 * ARP based queueing.
 *
 * @param p Head of pbuf chain to process
 *
 * @return Pointer to new head of pbuf chain 
 */
struct pbuf *
pbuf_take(struct pbuf *p)
{
  struct pbuf *q , *prev, *head;
  LWIP_ASSERT("pbuf_take: p != NULL\n", p != NULL);
  DEBUGF(PBUF_DEBUG | DBG_TRACE | 3, ("pbuf_take(%p)\n", (void*)p));

  prev = NULL;
  head = p;
  /* iterate through pbuf chain */
  do
  {
    /* pbuf is of type PBUF_REF? */
    if (p->flags == PBUF_FLAG_REF) {
      DEBUGF(PBUF_DEBUG | DBG_TRACE, ("pbuf_take: encountered PBUF_REF %p\n", (void *)p));
      /* allocate a pbuf (w/ payload) fully in RAM */
      /* PBUF_POOL buffers are faster if we can use them */
      if (p->len <= PBUF_POOL_BUFSIZE) {
        q = pbuf_alloc(PBUF_RAW, p->len, PBUF_POOL);
        if (q == NULL) DEBUGF(PBUF_DEBUG | DBG_TRACE | 2, ("pbuf_take: Could not allocate PBUF_POOL\n"));
      } else {
      	/* no replacement pbuf yet */
        q = NULL;
        DEBUGF(PBUF_DEBUG | DBG_TRACE | 2, ("pbuf_take: PBUF_POOL too small to replace PBUF_REF\n"));
      }
      /* no (large enough) PBUF_POOL was available? retry with PBUF_RAM */
      if (q == NULL) {
        q = pbuf_alloc(PBUF_RAW, p->len, PBUF_RAM);
        if (q == NULL) DEBUGF(PBUF_DEBUG | DBG_TRACE | 2, ("pbuf_take: Could not allocate PBUF_RAM\n"));
      }
      /* replacement pbuf could be allocated? */
      if (q != NULL)
      {
        /* copy p to q */  
        /* copy successor */
        q->next = p->next;
        /* remove linkage from original pbuf */
        p->next = NULL;
        /* remove linkage to original pbuf */
        if (prev != NULL) {
          /* prev->next == p at this point */
          LWIP_ASSERT("prev->next == p", prev->next == p);
          /* break chain and insert new pbuf instead */
          prev->next = q;
        /* prev == NULL, so we replaced the head pbuf of the chain */
        } else {
          head = q;
        }
        /* copy pbuf payload */
        memcpy(q->payload, p->payload, p->len);
        q->tot_len = p->tot_len;
        q->len = p->len;
        /* in case p was the first pbuf, it is no longer refered to by
         * our caller, as the caller MUST do p = pbuf_take(p);
         * in case p was not the first pbuf, it is no longer refered to
         * by prev. we can safely free the pbuf here.
         * (note that we have set p->next to NULL already so that
         * we will not free the rest of the chain by accident.)
         */
        pbuf_free(p);
        /* do not copy ref, since someone else might be using the old buffer */
        DEBUGF(PBUF_DEBUG, ("pbuf_take: replaced PBUF_REF %p with %p\n", (void *)p, (void *)q));
        p = q;
      } else {
        /* deallocate chain */
        pbuf_free(head);
        DEBUGF(PBUF_DEBUG | 2, ("pbuf_take: failed to allocate replacement pbuf for %p\n", (void *)p));
        return NULL;
      }
    /* p->flags != PBUF_FLAG_REF */
    } else {
      DEBUGF(PBUF_DEBUG | DBG_TRACE | 1, ("pbuf_take: skipping pbuf not of type PBUF_REF\n"));
    }
    /* remember this pbuf */
    prev = p;
    /* proceed to next pbuf in original chain */
    p = p->next;
  } while (p);
  DEBUGF(PBUF_DEBUG | DBG_TRACE | 1, ("pbuf_take: end of chain reached.\n"));
  
  return head;
}