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IOBs: Move from driver/iob to a better location in mm/iob
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Gregory Nutt
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/****************************************************************************
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* mm/iob/iob_alloc_qentry.c
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*
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* Copyright (C) 2014, 2016 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 <semaphore.h>
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#include <assert.h>
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#include <errno.h>
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#include <nuttx/irq.h>
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#include <nuttx/arch.h>
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#include <nuttx/mm/iob.h>
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#include "iob.h"
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#if CONFIG_IOB_NCHAINS > 0
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/****************************************************************************
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* Private Functions
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****************************************************************************/
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/****************************************************************************
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* Name: iob_allocwait_qentry
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*
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* Description:
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* Allocate an I/O buffer chain container by taking the buffer at the head
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* of the free list. This function is intended only for internal use by
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* the IOB module.
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*
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****************************************************************************/
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static FAR struct iob_qentry_s *iob_allocwait_qentry(void)
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{
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FAR struct iob_qentry_s *qentry;
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irqstate_t flags;
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int ret = OK;
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/* The following must be atomic; interrupt must be disabled so that there
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* is no conflict with interrupt level I/O buffer chain container
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* allocations. This is not as bad as it sounds because interrupts will be
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* re-enabled while we are waiting for I/O buffers to become free.
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*/
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flags = enter_critical_section();
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do
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{
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/* Try to get an I/O buffer chain container. If successful, the
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* semaphore count will be decremented atomically.
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*/
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qentry = iob_tryalloc_qentry();
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if (!qentry)
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{
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/* If not successful, then the semaphore count was less than or
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* equal to zero (meaning that there are no free buffers). We
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* need to wait for an I/O buffer chain container to be released
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* when the semaphore count will be incremented.
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*/
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ret = sem_wait(&g_qentry_sem);
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if (ret < 0)
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{
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int errcode = get_errno();
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/* EINTR is not an error! EINTR simply means that we were
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* awakened by a signal and we should try again.
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*
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* REVISIT: Many end-user interfaces are required to return
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* with an error if EINTR is set. Most uses of this function
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* is in internal, non-user logic. But are there cases where
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* the error should be returned.
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*/
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if (errcode == EINTR)
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{
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/* Force a success indication so that we will continue
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* looping.
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*/
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ret = 0;
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}
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else
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{
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/* Stop the loop and return a error */
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DEBUGASSERT(errcode > 0);
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ret = -errcode;
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}
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}
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else
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{
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/* When we wake up from wait successfully, an I/O buffer chain
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* container was returned to the free list. However, if there
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* are concurrent allocations from interrupt handling, then I
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* suspect that there is a race condition. But no harm, we
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* will just wait again in that case.
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*
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* We need release our count so that it is available to
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* iob_tryalloc_qentry(), perhaps allowing another thread to
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* take our count. In that event, iob_tryalloc_qentry() will
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* fail above and we will have to wait again.
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*
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* TODO: Consider a design modification to permit us to
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* complete the allocation without losing our count.
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*/
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sem_post(&g_qentry_sem);
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}
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}
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}
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while (ret == OK && !qentry);
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leave_critical_section(flags);
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return qentry;
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}
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: iob_alloc_qentry
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*
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* Description:
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* Allocate an I/O buffer chain container by taking the buffer at the head
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* of the free list. This function is intended only for internal use by
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* the IOB module.
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*
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****************************************************************************/
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FAR struct iob_qentry_s *iob_alloc_qentry(void)
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{
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/* Were we called from the interrupt level? */
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if (up_interrupt_context())
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{
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/* Yes, then try to allocate an I/O buffer without waiting */
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return iob_tryalloc_qentry();
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}
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else
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{
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/* Then allocate an I/O buffer, waiting as necessary */
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return iob_allocwait_qentry();
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}
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}
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/****************************************************************************
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* Name: iob_tryalloc_qentry
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*
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* Description:
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* Try to allocate an I/O buffer chain container by taking the buffer at
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* the head of the free list without waiting for the container to become
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* free. This function is intended only for internal use by the IOB module.
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*
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****************************************************************************/
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FAR struct iob_qentry_s *iob_tryalloc_qentry(void)
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{
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FAR struct iob_qentry_s *iobq;
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irqstate_t flags;
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/* We don't know what context we are called from so we use extreme measures
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* to protect the free list: We disable interrupts very briefly.
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*/
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flags = enter_critical_section();
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iobq = g_iob_freeqlist;
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if (iobq)
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{
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/* Remove the I/O buffer chain container from the free list and
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* decrement the counting semaphore that tracks the number of free
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* containers.
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*/
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g_iob_freeqlist = iobq->qe_flink;
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/* Take a semaphore count. Note that we cannot do this in
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* in the orthodox way by calling sem_wait() or sem_trywait()
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* because this function may be called from an interrupt
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* handler. Fortunately we know at at least one free buffer
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* so a simple decrement is all that is needed.
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*/
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g_qentry_sem.semcount--;
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DEBUGASSERT(g_qentry_sem.semcount >= 0);
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/* Put the I/O buffer in a known state */
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iobq->qe_head = NULL; /* Nothing is contained */
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}
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leave_critical_section(flags);
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return iobq;
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}
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#endif /* CONFIG_IOB_NCHAINS > 0 */
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