139 lines
4.4 KiB
C
139 lines
4.4 KiB
C
/****************************************************************************
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* drivers/iob/iob_trimtail.c
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*
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* Copyright (C) 2014, 2017 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <string.h>
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#include <debug.h>
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#include <nuttx/drivers/iob.h>
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#include "iob.h"
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: iob_trimtail
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*
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* Description:
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* Remove bytes from the end of an I/O chain
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*
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****************************************************************************/
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FAR struct iob_s *iob_trimtail(FAR struct iob_s *iob, unsigned int trimlen)
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{
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FAR struct iob_s *entry;
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FAR struct iob_s *penultimate;
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FAR struct iob_s *last;
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int len;
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iobinfo("iob=%p pktlen=%d trimlen=%d\n", iob, iob->io_pktlen, trimlen);
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if (iob && trimlen > 0)
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{
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len = trimlen;
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/* Loop until complete the trim */
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while (len > 0)
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{
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/* Calculate the total length of the data in the I/O buffer
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* chain and find the last entry in the chain.
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*/
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penultimate = NULL;
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last = NULL;
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for (entry = iob; entry; entry = entry->io_flink)
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{
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/* Remember the last and the next to the last in the chain */
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penultimate = last;
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last = entry;
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}
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/* Trim from the last entry in the chain. Do we trim this entire
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* I/O buffer away?
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*/
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iobinfo("iob=%p len=%d vs %d\n", last, last->io_len, len);
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if (last->io_len <= len)
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{
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/* Yes.. Consume the entire buffer */
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iob->io_pktlen -= last->io_len;
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len -= last->io_len;
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last->io_len = 0;
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/* Free the last, empty buffer in the list */
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iob_free(last);
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/* There should be a buffer before this one */
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if (!penultimate)
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{
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/* No.. we just freed the head of the chain */
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return NULL;
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}
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/* Unlink the penultimate from the freed buffer */
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penultimate->io_flink = NULL;
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}
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else
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{
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/* No, then just take what we need from this I/O buffer and
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* stop the trim.
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*/
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iob->io_pktlen -= len;
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last->io_len -= len;
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len = 0;
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}
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}
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}
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return iob;
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}
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