pbuf.c

FreeRTOS is a portable, open source, mini Real Time Kernel - a free to download and royalty free RTO

/**
 * @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 <[e-mail]>
 *
 */

#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"

#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)

/**
 * 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 | 3, ("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 | 3, ("pbuf_alloc: allocated pbuf %p\n", (void *)p));
    if (p == NULL) {
      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));
    /* 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) {
        /* 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_TRACE | 2, ("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 | 3, ("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: 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;
  }
  /* 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 | 2, ("pbuf_header: failed as %p < %p (not enough space for new header size)\n",
        (void *)p->payload,
        (void *)(p + 1)));\
      /* restore old payload pointer */