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 /**
  * @file
  * Packet buffer management
  *
  * Packets are built from the pbuf data structure. It supports dynamic
  * memory allocation for packet contents or can reference externally
  * managed packet contents both in RAM and ROM. Quick allocation for
  * incoming packets is provided through pools with fixed sized pbufs.
  *
  * A packet may span over multiple pbufs, chained as a singly linked
  * list. This is called a "pbuf chain".
  *
  * Multiple packets may be queued, also using this singly linked list.
  * This is called a "packet queue".
  * 
  * So, a packet queue consists of one or more pbuf chains, each of
  * which consist of one or more pbufs. CURRENTLY, PACKET QUEUES ARE
  * NOT SUPPORTED!!! Use helper structs to queue multiple packets.
  * 
  * The differences between a pbuf chain and a packet queue are very
  * precise but subtle. 
  *
  * The last pbuf of a packet has a ->tot_len field that equals the
  * ->len field. It can be found by traversing the list. If the last
  * pbuf of a packet has a ->next field other than NULL, more packets
  * are on the queue.
  *
  * Therefore, looping through a pbuf of a single packet, has an
  * loop end condition (tot_len == p->len), NOT (next == NULL).
  */
 
 /*
  * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
  * All rights reserved.
  *
  * 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. The name of the author may not be used to endorse or promote products
  *    derived from this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
  *
  * This file is part of the lwIP TCP/IP stack.
  *
  * Author: Adam Dunkels <adam@sics.se>
  *
  */
 
 #include "lwip/opt.h"
 
 #include "lwip/stats.h"
 #include "lwip/def.h"
 #include "lwip/mem.h"
 #include "lwip/memp.h"
 #include "lwip/pbuf.h"
 #include "lwip/sys.h"
 #include "arch/perf.h"
 #if TCP_QUEUE_OOSEQ
 #include "lwip/tcp.h"
 #endif
 
 #include <string.h>
 
 #define SIZEOF_STRUCT_PBUF        LWIP_MEM_ALIGN_SIZE(sizeof(struct pbuf))
 /* Since the pool is created in memp, PBUF_POOL_BUFSIZE will be automatically
    aligned there. Therefore, PBUF_POOL_BUFSIZE_ALIGNED can be used here. */
 #define PBUF_POOL_BUFSIZE_ALIGNED LWIP_MEM_ALIGN_SIZE(PBUF_POOL_BUFSIZE)
 
 #if !TCP_QUEUE_OOSEQ || NO_SYS
 #define PBUF_POOL_IS_EMPTY()
 #else /* !TCP_QUEUE_OOSEQ || NO_SYS */
 /** Define this to 0 to prevent freeing ooseq pbufs when the PBUF_POOL is empty */
 #ifndef PBUF_POOL_FREE_OOSEQ
 #define PBUF_POOL_FREE_OOSEQ 1
 #endif /* PBUF_POOL_FREE_OOSEQ */
 
 #if PBUF_POOL_FREE_OOSEQ
 #include "lwip/tcpip.h"
 #define PBUF_POOL_IS_EMPTY() pbuf_pool_is_empty()
 static u8_t pbuf_free_ooseq_queued;
 /**
  * Attempt to reclaim some memory from queued out-of-sequence TCP segments
  * if we run out of pool pbufs. It's better to give priority to new packets
  * if we're running out.
  *
  * This must be done in the correct thread context therefore this function
  * can only be used with NO_SYS=0 and through tcpip_callback.
  */
 static void
 pbuf_free_ooseq(void* arg)
 {
   struct tcp_pcb* pcb;
   SYS_ARCH_DECL_PROTECT(old_level);
   LWIP_UNUSED_ARG(arg);
 
   SYS_ARCH_PROTECT(old_level);
   pbuf_free_ooseq_queued = 0;
   SYS_ARCH_UNPROTECT(old_level);
 
   for (pcb = tcp_active_pcbs; NULL != pcb; pcb = pcb->next) {
     if (NULL != pcb->ooseq) {
       /** Free the ooseq pbufs of one PCB only */
       LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_free_ooseq: freeing out-of-sequence pbufs\n"));
       tcp_segs_free(pcb->ooseq);
       pcb->ooseq = NULL;
       return;
     }
   }
 }
 
 /** Queue a call to pbuf_free_ooseq if not already queued. */
 static void
 pbuf_pool_is_empty(void)
 {
   u8_t queued;
   SYS_ARCH_DECL_PROTECT(old_level);
 
   SYS_ARCH_PROTECT(old_level);
   queued = pbuf_free_ooseq_queued;
   pbuf_free_ooseq_queued = 1;
   SYS_ARCH_UNPROTECT(old_level);
 
   if(!queued) {
     /* queue a call to pbuf_free_ooseq if not already queued */
     if(tcpip_callback_with_block(pbuf_free_ooseq, NULL, 0) != ERR_OK) {
       SYS_ARCH_PROTECT(old_level);
       pbuf_free_ooseq_queued = 0;
       SYS_ARCH_UNPROTECT(old_level);
     }
   }
 }
 #endif /* PBUF_POOL_FREE_OOSEQ */
 #endif /* !TCP_QUEUE_OOSEQ || NO_SYS */
 
 /**
  * Allocates a pbuf of the given type (possibly a chain for PBUF_POOL type).
  *
  * The actual memory allocated for the pbuf is determined by the
  * layer at which the pbuf is allocated and the requested size
  * (from the size parameter).
  *
  * @param layer flag to define header size
  * @param length size of the pbuf's payload
  * @param type this parameter decides how and where the pbuf
  * should be allocated as follows:
  *
  * - PBUF_RAM: buffer memory for pbuf is allocated as one large
  *             chunk. This includes protocol headers as well.
  * - PBUF_ROM: no buffer memory is allocated for the pbuf, even for
  *             protocol headers. Additional headers must be prepended
  *             by allocating another pbuf and chain in to the front of
  *             the ROM pbuf. It is assumed that the memory used is really
  *             similar to ROM in that it is immutable and will not be
  *             changed. Memory which is dynamic should generally not
  *             be attached to PBUF_ROM pbufs. Use PBUF_REF instead.
  * - PBUF_REF: no buffer memory is allocated for the pbuf, even for
  *             protocol headers. It is assumed that the pbuf is only
  *             being used in a single thread. If the pbuf gets queued,
  *             then pbuf_take should be called to copy the buffer.
  * - PBUF_POOL: the pbuf is allocated as a pbuf chain, with pbufs from
  *              the pbuf pool that is allocated during pbuf_init().
  *
  * @return the allocated pbuf. If multiple pbufs where allocated, this
  * is the first pbuf of a pbuf chain.
  */
 struct pbuf *
 pbuf_alloc(pbuf_layer layer, u16_t length, pbuf_type type)
 {
   struct pbuf *p, *q, *r;
   u16_t offset;
   s32_t rem_len; /* remaining length */
   LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_alloc(length=%"U16_F")\n", length));
 
   /* determine header offset */
   offset = 0;
   switch (layer) {
   case PBUF_TRANSPORT:
     /* add room for transport (often TCP) layer header */
     offset += PBUF_TRANSPORT_HLEN;
     /* FALLTHROUGH */
   case PBUF_IP:
     /* add room for IP layer header */
     offset += PBUF_IP_HLEN;
     /* FALLTHROUGH */
   case PBUF_LINK:
     /* add room for link layer header */
     offset += PBUF_LINK_HLEN;
     break;
   case PBUF_RAW:
     break;
   default:
     LWIP_ASSERT("pbuf_alloc: bad pbuf layer", 0);
     return NULL;
   }
 
   switch (type) {
   case PBUF_POOL:
     /* allocate head of pbuf chain into p */
     p = memp_malloc(MEMP_PBUF_POOL);
     LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_alloc: allocated pbuf %p\n", (void *)p));
     if (p == NULL) {
       PBUF_POOL_IS_EMPTY();
       return NULL;
     }
     p->type = type;
     p->next = NULL;
 
     /* make the payload pointer point 'offset' bytes into pbuf data memory */
     p->payload = LWIP_MEM_ALIGN((void *)((u8_t *)p + (SIZEOF_STRUCT_PBUF + offset)));
     LWIP_ASSERT("pbuf_alloc: pbuf p->payload properly aligned",
             ((mem_ptr_t)p->payload % MEM_ALIGNMENT) == 0);
     /* the total length of the pbuf chain is the requested size */
     p->tot_len = length;
     /* set the length of the first pbuf in the chain */
     p->len = LWIP_MIN(length, PBUF_POOL_BUFSIZE_ALIGNED - LWIP_MEM_ALIGN_SIZE(offset));
     LWIP_ASSERT("check p->payload + p->len does not overflow pbuf",
                 ((u8_t*)p->payload + p->len <=
                  (u8_t*)p + SIZEOF_STRUCT_PBUF + PBUF_POOL_BUFSIZE_ALIGNED));
     LWIP_ASSERT("PBUF_POOL_BUFSIZE must be bigger than MEM_ALIGNMENT",
       (PBUF_POOL_BUFSIZE_ALIGNED - LWIP_MEM_ALIGN_SIZE(offset)) > 0 );
     /* set reference count (needed here in case we fail) */
     p->ref = 1;
 
     /* now allocate the tail of the pbuf chain */
 
     /* remember first pbuf for linkage in next iteration */
     r = p;
     /* remaining length to be allocated */
     rem_len = length - p->len;
     /* any remaining pbufs to be allocated? */
     while (rem_len > 0) {
       q = memp_malloc(MEMP_PBUF_POOL);
       if (q == NULL) {
         PBUF_POOL_IS_EMPTY();
         /* free chain so far allocated */
         pbuf_free(p);
         /* bail out unsuccesfully */
         return NULL;
       }
       q->type = type;
       q->flags = 0;
       q->next = NULL;
       /* make previous pbuf point to this pbuf */
       r->next = q;
       /* set total length of this pbuf and next in chain */
       LWIP_ASSERT("rem_len < max_u16_t", rem_len < 0xffff);
       q->tot_len = (u16_t)rem_len;
       /* this pbuf length is pool size, unless smaller sized tail */
       q->len = LWIP_MIN((u16_t)rem_len, PBUF_POOL_BUFSIZE_ALIGNED);
       q->payload = (void *)((u8_t *)q + SIZEOF_STRUCT_PBUF);
       LWIP_ASSERT("pbuf_alloc: pbuf q->payload properly aligned",
               ((mem_ptr_t)q->payload % MEM_ALIGNMENT) == 0);
       LWIP_ASSERT("check p->payload + p->len does not overflow pbuf",
                   ((u8_t*)p->payload + p->len <=
                    (u8_t*)p + SIZEOF_STRUCT_PBUF + PBUF_POOL_BUFSIZE_ALIGNED));
       q->ref = 1;
       /* calculate remaining length to be allocated */
       rem_len -= q->len;
       /* remember this pbuf for linkage in next iteration */
       r = q;
     }
     /* end of chain */
     /*r->next = NULL;*/
 
     break;
   case PBUF_RAM:
     /* If pbuf is to be allocated in RAM, allocate memory for it. */
     p = (struct pbuf*)mem_malloc(LWIP_MEM_ALIGN_SIZE(SIZEOF_STRUCT_PBUF + offset) + LWIP_MEM_ALIGN_SIZE(length));
     if (p == NULL) {
       return NULL;
     }
     /* Set up internal structure of the pbuf. */
     p->payload = LWIP_MEM_ALIGN((void *)((u8_t *)p + SIZEOF_STRUCT_PBUF + offset));
     p->len = p->tot_len = length;
     p->next = NULL;
     p->type = type;
 
     LWIP_ASSERT("pbuf_alloc: pbuf->payload properly aligned",
            ((mem_ptr_t)p->payload % MEM_ALIGNMENT) == 0);
     break;
   /* pbuf references existing (non-volatile static constant) ROM payload? */
   case PBUF_ROM:
   /* pbuf references existing (externally allocated) RAM payload? */
   case PBUF_REF:
     /* only allocate memory for the pbuf structure */
     p = memp_malloc(MEMP_PBUF);
     if (p == NULL) {
       LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
                   ("pbuf_alloc: Could not allocate MEMP_PBUF for PBUF_%s.\n",
                   (type == PBUF_ROM) ? "ROM" : "REF"));
       return NULL;
     }
     /* caller must set this field properly, afterwards */
     p->payload = NULL;
     p->len = p->tot_len = length;
     p->next = NULL;
     p->type = type;
     break;
   default:
     LWIP_ASSERT("pbuf_alloc: erroneous type", 0);
     return NULL;
   }
   /* set reference count */
   p->ref = 1;
   /* set flags */
   p->flags = 0;
   LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_alloc(length=%"U16_F") == %p\n", length, (void *)p));
   return p;
 }
 
 
 /**
  * Shrink a pbuf chain to a desired length.
  *
  * @param p pbuf to shrink.
  * @param new_len desired new length of pbuf chain
  *
  * Depending on the desired length, the first few pbufs in a chain might
  * be skipped and left unchanged. The new last pbuf in the chain will be
  * resized, and any remaining pbufs will be freed.
  *
  * @note If the pbuf is ROM/REF, only the ->tot_len and ->len fields are adjusted.
  * @note May not be called on a packet queue.
  *
  * @note Despite its name, pbuf_realloc cannot grow the size of a pbuf (chain).
  */
 void
 pbuf_realloc(struct pbuf *p, u16_t new_len)
 {
   struct pbuf *q;
   u16_t rem_len; /* remaining length */
   s32_t grow;
 
   LWIP_ASSERT("pbuf_realloc: p != NULL", p != NULL);
   LWIP_ASSERT("pbuf_realloc: sane p->type", p->type == PBUF_POOL ||
               p->type == PBUF_ROM ||
               p->type == PBUF_RAM ||
               p->type == PBUF_REF);
 
   /* desired length larger than current length? */
   if (new_len >= p->tot_len) {
     /* enlarging not yet supported */
     return;
   }
 
   /* the pbuf chain grows by (new_len - p->tot_len) bytes
    * (which may be negative in case of shrinking) */
   grow = new_len - p->tot_len;
 
   /* first, step over any pbufs that should remain in the chain */
   rem_len = new_len;
   q = p;
   /* should this pbuf be kept? */
   while (rem_len > q->len) {
     /* decrease remaining length by pbuf length */
     rem_len -= q->len;
     /* decrease total length indicator */
     LWIP_ASSERT("grow < max_u16_t", grow < 0xffff);
     q->tot_len += (u16_t)grow;
     /* proceed to next pbuf in chain */
     q = q->next;
     LWIP_ASSERT("pbuf_realloc: q != NULL", q != NULL);
   }
   /* we have now reached the new last pbuf (in q) */
   /* rem_len == desired length for pbuf q */
 
   /* shrink allocated memory for PBUF_RAM */
   /* (other types merely adjust their length fields */
   if ((q->type == PBUF_RAM) && (rem_len != q->len)) {
     /* reallocate and adjust the length of the pbuf that will be split */
     q = mem_realloc(q, (u8_t *)q->payload - (u8_t *)q + rem_len);
     LWIP_ASSERT("mem_realloc give q == NULL", q != NULL);
   }
   /* adjust length fields for new last pbuf */
   q->len = rem_len;
   q->tot_len = q->len;
 
   /* any remaining pbufs in chain? */
   if (q->next != NULL) {
     /* free remaining pbufs in chain */
     pbuf_free(q->next);
   }
   /* q is last packet in chain */
   q->next = NULL;
 
 }
 
 /**
  * Adjusts the payload pointer to hide or reveal headers in the payload.
  *
  * Adjusts the ->payload pointer so that space for a header
  * (dis)appears in the pbuf payload.
  *
  * The ->payload, ->tot_len and ->len fields are adjusted.
  *
  * @param p pbuf to change the header size.
  * @param header_size_increment Number of bytes to increment header size which
  * increases the size of the pbuf. New space is on the front.
  * (Using a negative value decreases the header size.)
  * If hdr_size_inc is 0, this function does nothing and returns succesful.
  *
  * PBUF_ROM and PBUF_REF type buffers cannot have their sizes increased, so
  * the call will fail. A check is made that the increase in header size does
  * not move the payload pointer in front of the start of the buffer.
  * @return non-zero on failure, zero on success.
  *
  */
 u8_t
 pbuf_header(struct pbuf *p, s16_t header_size_increment)
 {
   u16_t type;
   void *payload;
   u16_t increment_magnitude;
 
   LWIP_ASSERT("p != NULL", p != NULL);
   if ((header_size_increment == 0) || (p == NULL))
     return 0;
  
   if (header_size_increment < 0){
     increment_magnitude = -header_size_increment;
     /* Check that we aren't going to move off the end of the pbuf */
     LWIP_ERROR("increment_magnitude <= p->len", (increment_magnitude <= p->len), return 1;);
   } else {
     increment_magnitude = header_size_increment;
 #if 0
     /* Can't assert these as some callers speculatively call
          pbuf_header() to see if it's OK.  Will return 1 below instead. */
     /* Check that we've got the correct type of pbuf to work with */
     LWIP_ASSERT("p->type == PBUF_RAM || p->type == PBUF_POOL", 
                 p->type == PBUF_RAM || p->type == PBUF_POOL);
     /* Check that we aren't going to move off the beginning of the pbuf */
     LWIP_ASSERT("p->payload - increment_magnitude >= p + SIZEOF_STRUCT_PBUF",
                 (u8_t *)p->payload - increment_magnitude >= (u8_t *)p + SIZEOF_STRUCT_PBUF);
 #endif
   }
 
   type = p->type;
   /* remember current payload pointer */
   payload = p->payload;
 
   /* pbuf types containing payloads? */
   if (type == PBUF_RAM || type == PBUF_POOL) {
     /* set new payload pointer */
     p->payload = (u8_t *)p->payload - header_size_increment;
     /* boundary check fails? */
     if ((u8_t *)p->payload < (u8_t *)p + SIZEOF_STRUCT_PBUF) {
       LWIP_DEBUGF( PBUF_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
         ("pbuf_header: failed as %p < %p (not enough space for new header size)\n",
         (void *)p->payload, (void *)(p + 1)));
       /* restore old payload pointer */
       p->payload = payload;
       /* bail out unsuccesfully */
       return 1;
     }
   /* pbuf types refering to external payloads? */
   } else if (type == PBUF_REF || type == PBUF_ROM) {
     /* hide a header in the payload? */
     if ((header_size_increment < 0) && (increment_magnitude <= p->len)) {
       /* increase payload pointer */
       p->payload = (u8_t *)p->payload - header_size_increment;
     } else {
       /* cannot expand payload to front (yet!)
        * bail out unsuccesfully */
       return 1;
     }
   }
   else {
     /* Unknown type */
     LWIP_ASSERT("bad pbuf type", 0);
     return 1;
   }
   /* modify pbuf length fields */
   p->len += header_size_increment;
   p->tot_len += header_size_increment;
 
   LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_header: old %p new %p (%"S16_F")\n",
     (void *)payload, (void *)p->payload, header_size_increment));
 
   return 0;
 }
 
 /**
  * Dereference a pbuf chain or queue and deallocate any no-longer-used
  * pbufs at the head of this chain or queue.
  *
  * Decrements the pbuf reference count. If it reaches zero, the pbuf is
  * deallocated.
  *
  * For a pbuf chain, this is repeated for each pbuf in the chain,
  * up to the first pbuf which has a non-zero reference count after
  * decrementing. So, when all reference counts are one, the whole
  * chain is free'd.
  *
  * @param p The pbuf (chain) to be dereferenced.
  *
  * @return the number of pbufs that were de-allocated
  * from the head of the chain.
  *
  * @note MUST NOT be called on a packet queue (Not verified to work yet).
  * @note the reference counter of a pbuf equals the number of pointers
  * that refer to the pbuf (or into the pbuf).
  *
  * @internal examples:
  *
  * Assuming existing chains a->b->c with the following reference
  * counts, calling pbuf_free(a) results in:
  * 
  * 1->2->3 becomes ...1->3
  * 3->3->3 becomes 2->3->3
  * 1->1->2 becomes ......1
  * 2->1->1 becomes 1->1->1
  * 1->1->1 becomes .......
  *
  */
 u8_t
 pbuf_free(struct pbuf *p)
 {
   u16_t type;
   struct pbuf *q;
   u8_t count;
 
   if (p == NULL) {
     LWIP_ASSERT("p != NULL", p != NULL);
     /* if assertions are disabled, proceed with debug output */
     LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
       ("pbuf_free(p == NULL) was called.\n"));
     return 0;
   }
   LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_free(%p)\n", (void *)p));
 
   PERF_START;
 
   LWIP_ASSERT("pbuf_free: sane type",
     p->type == PBUF_RAM || p->type == PBUF_ROM ||
     p->type == PBUF_REF || p->type == PBUF_POOL);
 
   count = 0;
   /* de-allocate all consecutive pbufs from the head of the chain that
    * obtain a zero reference count after decrementing*/
   while (p != NULL) {
     u16_t ref;
     SYS_ARCH_DECL_PROTECT(old_level);
     /* Since decrementing ref cannot be guaranteed to be a single machine operation
      * we must protect it. We put the new ref into a local variable to prevent
      * further protection. */
     SYS_ARCH_PROTECT(old_level);
     /* all pbufs in a chain are referenced at least once */
     LWIP_ASSERT("pbuf_free: p->ref > 0", p->ref > 0);
     /* decrease reference count (number of pointers to pbuf) */
     ref = --(p->ref);
     SYS_ARCH_UNPROTECT(old_level);
     /* this pbuf is no longer referenced to? */
     if (ref == 0) {
       /* remember next pbuf in chain for next iteration */
       q = p->next;
       LWIP_DEBUGF( PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_free: deallocating %p\n", (void *)p));
       type = p->type;
       /* is this a pbuf from the pool? */
       if (type == PBUF_POOL) {
         memp_free(MEMP_PBUF_POOL, p);
       /* is this a ROM or RAM referencing pbuf? */
       } else if (type == PBUF_ROM || type == PBUF_REF) {
         memp_free(MEMP_PBUF, p);
       /* type == PBUF_RAM */
       } else {
         mem_free(p);
       }
       count++;
       /* proceed to next pbuf */
       p = q;
     /* p->ref > 0, this pbuf is still referenced to */
     /* (and so the remaining pbufs in chain as well) */
     } else {
       LWIP_DEBUGF( PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_free: %p has ref %"U16_F", ending here.\n", (void *)p, ref));
       /* stop walking through the chain */
       p = NULL;
     }
   }
   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)
 {
   SYS_ARCH_DECL_PROTECT(old_level);
   /* pbuf given? */
   if (p != NULL) {
     SYS_ARCH_PROTECT(old_level);
     ++(p->ref);
     SYS_ARCH_UNPROTECT(old_level);
   }
 }
 
 /**
  * Concatenate two pbufs (each may be a pbuf chain) and take over
  * the caller's reference of the tail pbuf.
  * 
  * @note The caller MAY NOT reference the tail pbuf afterwards.
  * Use pbuf_chain() for that purpose.
  * 
  * @see pbuf_chain()
  */
 
 void
 pbuf_cat(struct pbuf *h, struct pbuf *t)
 {
   struct pbuf *p;
 
   LWIP_ERROR("(h != NULL) && (t != NULL) (programmer violates API)",
              ((h != NULL) && (t != NULL)), return;);
 
   /* 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, p->next == NULL } */
   LWIP_ASSERT("p->tot_len == p->len (of last pbuf in chain)", p->tot_len == p->len);
   LWIP_ASSERT("p->next == NULL", p->next == NULL);
   /* add total length of second chain to last pbuf total of first chain */
   p->tot_len += t->tot_len;
   /* chain last pbuf of head (p) with first of tail (t) */
   p->next = t;
   /* p->next now references t, but the caller will drop its reference to t,
    * so netto there is no change to the reference count of t.
    */
 }
 
 /**
  * Chain two pbufs (or pbuf chains) together.
  * 
  * The caller MUST call pbuf_free(t) once it has stopped
  * using it. Use pbuf_cat() instead if you no longer use t.
  * 
  * @param h head pbuf (chain)
  * @param t tail pbuf (chain)
  * @note The pbufs MUST belong to the same packet.
  * @note MAY NOT be called on a packet queue.
  *
  * The ->tot_len fields of all pbufs of the head chain are adjusted.
  * The ->next field of the last pbuf of the head chain is adjusted.
  * The ->ref field of the first pbuf of the tail chain is adjusted.
  *
  */
 void
 pbuf_chain(struct pbuf *h, struct pbuf *t)
 {
   pbuf_cat(h, t);
   /* t is now referenced by h */
   pbuf_ref(t);
   LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_chain: %p references %p\n", (void *)h, (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.
  * @note May not be called on a packet queue.
  */
 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 */
     LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_dechain: unreferencing %p\n", (void *)q));
     tail_gone = pbuf_free(q);
     if (tail_gone > 0) {
       LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE,
                   ("pbuf_dechain: deallocated %p (as it is no longer referenced)\n", (void *)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_RAM copies of pbufs.
  *
  * Used to queue packets on behalf of the lwIP stack, such as
  * ARP based queueing.
  *
  * @note You MUST explicitly use p = pbuf_take(p);
  *
  * @note Only one packet is copied, no packet queue!
  *
  * @param p_to pbuf destination of the copy
  * @param p_from pbuf source of the copy
  *
  * @return ERR_OK if pbuf was copied
  *         ERR_ARG if one of the pbufs is NULL or p_to is not big
  *                 enough to hold p_from
  */
 err_t
 pbuf_copy(struct pbuf *p_to, struct pbuf *p_from)
 {
   u16_t offset_to=0, offset_from=0, len;
 
   LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_copy(%p, %p)\n",
     (void*)p_to, (void*)p_from));
 
   /* is the target big enough to hold the source? */
   LWIP_ERROR("pbuf_copy: target not big enough to hold source", ((p_to != NULL) &&
              (p_from != NULL) && (p_to->tot_len >= p_from->tot_len)), return ERR_ARG;);
 
   /* iterate through pbuf chain */
   do
   {
     LWIP_ASSERT("p_to != NULL", p_to != NULL);
     /* copy one part of the original chain */
     if ((p_to->len - offset_to) >= (p_from->len - offset_from)) {
       /* complete current p_from fits into current p_to */
       len = p_from->len - offset_from;
     } else {
       /* current p_from does not fit into current p_to */
       len = p_to->len - offset_to;
     }
     MEMCPY((u8_t*)p_to->payload + offset_to, (u8_t*)p_from->payload + offset_from, len);
     offset_to += len;
     offset_from += len;
     LWIP_ASSERT("offset_to <= p_to->len", offset_to <= p_to->len);
     if (offset_to == p_to->len) {
       /* on to next p_to (if any) */
       offset_to = 0;
       p_to = p_to->next;
     }
     LWIP_ASSERT("offset_from <= p_from->len", offset_from <= p_from->len);
     if (offset_from >= p_from->len) {
       /* on to next p_from (if any) */
       offset_from = 0;
       p_from = p_from->next;
     }
 
     if((p_from != NULL) && (p_from->len == p_from->tot_len)) {
       /* don't copy more than one packet! */
       LWIP_ERROR("pbuf_copy() does not allow packet queues!\n",
                  (p_from->next == NULL), return ERR_VAL;);
     }
     if((p_to != NULL) && (p_to->len == p_to->tot_len)) {
       /* don't copy more than one packet! */
       LWIP_ERROR("pbuf_copy() does not allow packet queues!\n",
                   (p_to->next == NULL), return ERR_VAL;);
     }
   } while (p_from);
   LWIP_DEBUGF(PBUF_DEBUG | LWIP_DBG_TRACE, ("pbuf_copy: end of chain reached.\n"));
   return ERR_OK;
 }
 
 /**
  * Copy (part of) the contents of a packet buffer
  * to an application supplied buffer.
  *
  * @param buf the pbuf from which to copy data
  * @param dataptr the application supplied buffer
  * @param len length of data to copy (dataptr must be big enough). No more 
  * than buf->tot_len will be copied, irrespective of len
  * @param offset offset into the packet buffer from where to begin copying len bytes
  * @return the number of bytes copied, or 0 on failure
  */
 u16_t
 pbuf_copy_partial(struct pbuf *buf, void *dataptr, u16_t len, u16_t offset)
 {
   struct pbuf *p;
   u16_t left;
   u16_t buf_copy_len;
   u16_t copied_total = 0;
 
   LWIP_ERROR("pbuf_copy_partial: invalid buf", (buf != NULL), return 0;);
   LWIP_ERROR("pbuf_copy_partial: invalid dataptr", (dataptr != NULL), return 0;);
 
   left = 0;
 
   if((buf == NULL) || (dataptr == NULL)) {
     return 0;
   }
 
   /* Note some systems use byte copy if dataptr or one of the pbuf payload pointers are unaligned. */
   for(p = buf; len != 0 && p != NULL; p = p->next) {
     if ((offset != 0) && (offset >= p->len)) {
       /* don't copy from this buffer -> on to the next */
       offset -= p->len;
     } else {
       /* copy from this buffer. maybe only partially. */
       buf_copy_len = p->len - offset;
       if (buf_copy_len > len)
           buf_copy_len = len;
       /* copy the necessary parts of the buffer */
       MEMCPY(&((char*)dataptr)[left], &((char*)p->payload)[offset], buf_copy_len);
       copied_total += buf_copy_len;
       left += buf_copy_len;
       len -= buf_copy_len;
       offset = 0;
     }
   }
   return copied_total;
 }
 
 /**
  * Copy application supplied data into a pbuf.
  * This function can only be used to copy the equivalent of buf->tot_len data.
  *
  * @param buf pbuf to fill with data
  * @param dataptr application supplied data buffer
  * @param len length of the application supplied data buffer
  *
  * @return ERR_OK if successful, ERR_MEM if the pbuf is not big enough
  */
 err_t
 pbuf_take(struct pbuf *buf, const void *dataptr, u16_t len)
 {
   struct pbuf *p;
   u16_t buf_copy_len;
   u16_t total_copy_len = len;
   u16_t copied_total = 0;
 
   LWIP_ERROR("pbuf_take: invalid buf", (buf != NULL), return 0;);
   LWIP_ERROR("pbuf_take: invalid dataptr", (dataptr != NULL), return 0;);
 
   if ((buf == NULL) || (dataptr == NULL) || (buf->tot_len < len)) {
     return ERR_ARG;
   }
 
   /* Note some systems use byte copy if dataptr or one of the pbuf payload pointers are unaligned. */
   for(p = buf; total_copy_len != 0; p = p->next) {
     LWIP_ASSERT("pbuf_take: invalid pbuf", p != NULL);
     buf_copy_len = total_copy_len;
     if (buf_copy_len > p->len) {
       /* this pbuf cannot hold all remaining data */
       buf_copy_len = p->len;
     }
     /* copy the necessary parts of the buffer */
     MEMCPY(p->payload, &((char*)dataptr)[copied_total], buf_copy_len);
     total_copy_len -= buf_copy_len;
     copied_total += buf_copy_len;
   }
   LWIP_ASSERT("did not copy all data", total_copy_len == 0 && copied_total == len);
   return ERR_OK;
 }
 
 /**
  * Creates a single pbuf out of a queue of pbufs.
  *
  * @remark: The source pbuf 'p' is not freed by this function because that can
  *          be illegal in some places!
  *
  * @param p the source pbuf
  * @param layer pbuf_layer of the new pbuf
  *
  * @return a new, single pbuf (p->next is NULL)
  *         or the old pbuf if allocation fails
  */
 struct pbuf*
 pbuf_coalesce(struct pbuf *p, pbuf_layer layer)
 {
   struct pbuf *q;
   err_t err;
   if (p->next == NULL) {
     return p;
   }
   q = pbuf_alloc(layer, p->tot_len, PBUF_RAM);
   if (q == NULL) {
     /* @todo: what do we do now? */
     return p;
   }
   err = pbuf_copy(q, p);
   LWIP_ASSERT("pbuf_copy failed", err == ERR_OK);
   pbuf_free(p);
   return q;
 }