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/****************************************************************************
* net/iob/iob_trimtail.c
*
* Copyright (C) 2014 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* 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/config.h>
#if defined(CONFIG_DEBUG) && defined(CONFIG_IOB_DEBUG)
/* Force debug output (from this file only) */
# undef CONFIG_DEBUG_NET
# define CONFIG_DEBUG_NET 1
#endif
#include <string.h>
#include <debug.h>
#include <nuttx/net/iob.h>
#include "iob.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Private Types
****************************************************************************/
/****************************************************************************
* Private Data
****************************************************************************/
/****************************************************************************
* Public Data
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: iob_trimtail
*
* Description:
* Remove bytes from the end of an I/O chain
*
****************************************************************************/
FAR struct iob_s *iob_trimtail(FAR struct iob_s *iob, unsigned int trimlen)
{
FAR struct iob_s *entry;
FAR struct iob_s *penultimate;
FAR struct iob_s *last;
unsigned int iosize;
int len;
nlldbg("iob=%p pktlen=%d trimlen=%d\n", iob, iob->io_pktlen, trimlen);
if (iob && trimlen > 0)
{
len = trimlen;
/* Loop until complete the trim */
while (len > 0)
{
/* Calculate the total length of the data in the I/O buffer
* chain and find the last entry in the chain.
*/
penultimate = NULL;
last = NULL;
iosize = 0;
for (entry = iob; entry; entry = entry->io_flink)
{
/* Accumulate the total size of all buffers in the list */
iosize += entry->io_len;
/* Remember the last and the next to the last in the chain */
penultimate = last;
last = entry;
}
/* Trim from the last entry in the chain. Do we trim this entire
* I/O buffer away?
*/
nllvdbg("iob=%p len=%d vs %d\n", last, last->io_len, len);
if (last->io_len <= len)
{
/* Yes.. Consume the entire buffer */
iob->io_pktlen -= last->io_len;
len -= last->io_len;
last->io_len = 0;
/* Free the last, empty buffer in the list */
iob_free(last);
/* There should be a buffer before this one */
if (!penultimate)
{
/* No.. we just freed the head of the chain */
return NULL;
}
/* Unlink the penultimate from the freed buffer */
penultimate->io_flink = NULL;
}
else
{
/* No, then just take what we need from this I/O buffer and
* stop the trim.
*/
iob->io_pktlen -= len;
last->io_len -= len;
len = 0;
}
}
}
return iob;
}
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