/****************************************************************************
* mm/iob/iob_alloc_qentry.c
*
* Copyright (C) 2014, 2016-2017 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>
#include <assert.h>
#include <errno.h>
#include <nuttx/irq.h>
#include <nuttx/arch.h>
#include <nuttx/mm/iob.h>
#include "iob.h"
#if CONFIG_IOB_NCHAINS > 0
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: iob_alloc_qcommitted
*
* Description:
* Allocate an I/O buffer by taking the buffer at the head of the committed
* list.
*
****************************************************************************/
static FAR struct iob_qentry_s *iob_alloc_qcommitted(void)
{
FAR struct iob_qentry_s *iobq = NULL;
irqstate_t flags;
/* We don't know what context we are called from so we use extreme measures
* to protect the committed list: We disable interrupts very briefly.
*/
flags = enter_critical_section();
/* Take the I/O buffer from the head of the committed list */
iobq = g_iob_qcommitted;
if (iobq != NULL)
{
/* Remove the I/O buffer from the committed list */
g_iob_qcommitted = iobq->qe_flink;
/* Put the I/O buffer in a known state */
iobq->qe_head = NULL; /* Nothing is contained */
}
leave_critical_section(flags);
return iobq;
}
/****************************************************************************
* Name: iob_allocwait_qentry
*
* Description:
* Allocate an I/O buffer chain container by taking the buffer at the head
* of the free list. This function is intended only for internal use by
* the IOB module.
*
****************************************************************************/
static FAR struct iob_qentry_s *iob_allocwait_qentry(void)
{
FAR struct iob_qentry_s *qentry;
irqstate_t flags;
int ret = OK;
/* The following must be atomic; interrupt must be disabled so that there
* is no conflict with interrupt level I/O buffer chain container
* allocations. This is not as bad as it sounds because interrupts will be
* re-enabled while we are waiting for I/O buffers to become free.
*/
flags = enter_critical_section();
/* Try to get an I/O buffer chain container. If successful, the semaphore
* count will bedecremented atomically.
*/
qentry = iob_tryalloc_qentry();
while (ret == OK && qentry == NULL)
{
/* If not successful, then the semaphore count was less than or equal
* to zero (meaning that there are no free buffers). We need to wait
* for an I/O buffer chain container to be released when the
* semaphore count will be incremented.
*/
ret = nxsem_wait_uninterruptible(&g_qentry_sem);
if (ret >= 0)
{
/* When we wake up from wait successfully, an I/O buffer chain
* container was freed and we hold a count for one IOB. Unless
* something failed, we should have an IOB waiting for us in the
* committed list.
*/
qentry = iob_alloc_qcommitted();
DEBUGASSERT(qentry != NULL);
if (qentry == NULL)
{
/* This should not fail, but we allow for that possibility to
* handle any potential, non-obvious race condition. Perhaps
* the free IOB ended up in the g_iob_free list?
*
* We need release our count so that it is available to
* iob_tryalloc(), perhaps allowing another thread to take our
* count. In that event, iob_tryalloc() will fail above and
* we will have to wait again.
*/
nxsem_post(&g_qentry_sem);
qentry = iob_tryalloc_qentry();
}
}
}
leave_critical_section(flags);
return qentry;
}
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: iob_alloc_qentry
*
* Description:
* Allocate an I/O buffer chain container by taking the buffer at the head
* of the free list. This function is intended only for internal use by
* the IOB module.
*
****************************************************************************/
FAR struct iob_qentry_s *iob_alloc_qentry(void)
{
/* Were we called from the interrupt level? */
if (up_interrupt_context() || sched_idletask())
{
/* Yes, then try to allocate an I/O buffer without waiting */
return iob_tryalloc_qentry();
}
else
{
/* Then allocate an I/O buffer, waiting as necessary */
return iob_allocwait_qentry();
}
}
/****************************************************************************
* Name: iob_tryalloc_qentry
*
* Description:
* Try to allocate an I/O buffer chain container by taking the buffer at
* the head of the free list without waiting for the container to become
* free. This function is intended only for internal use by the IOB module.
*
****************************************************************************/
FAR struct iob_qentry_s *iob_tryalloc_qentry(void)
{
FAR struct iob_qentry_s *iobq;
irqstate_t flags;
/* We don't know what context we are called from so we use extreme measures
* to protect the free list: We disable interrupts very briefly.
*/
flags = enter_critical_section();
iobq = g_iob_freeqlist;
if (iobq)
{
/* Remove the I/O buffer chain container from the free list and
* decrement the counting semaphore that tracks the number of free
* containers.
*/
g_iob_freeqlist = iobq->qe_flink;
/* Take a semaphore count. Note that we cannot do this in
* in the orthodox way by calling nxsem_wait() or nxsem_trywait()
* because this function may be called from an interrupt
* handler. Fortunately we know at at least one free buffer
* so a simple decrement is all that is needed.
*/
g_qentry_sem.semcount--;
DEBUGASSERT(g_qentry_sem.semcount >= 0);
/* Put the I/O buffer in a known state */
iobq->qe_head = NULL; /* Nothing is contained */
}
leave_critical_section(flags);
return iobq;
}
#endif /* CONFIG_IOB_NCHAINS > 0 */