/**************************************************************************** * mm/iob/iob_alloc_qentry.c * * Copyright (C) 2014, 2016-2017 Gregory Nutt. All rights reserved. * Author: Gregory Nutt * * 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 #include #include #include #include #include #include #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(&g_qentry_sem); if (ret < 0) { /* EINTR is not an error! EINTR simply means that we were * awakened by a signal and we should try again. * * REVISIT: Many end-user interfaces are required to return * with an error if EINTR is set. Most uses of this function * is in internal, non-user logic. But are there cases where * the error should be returned. */ if (ret == -EINTR) { /* Force a success indication so that we will continue looping. */ ret = OK; } } else { /* When we wake up from wait successfully, an I/O buffer chain container was * freed and we hold a count for one IOB. Unless somehting * 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 */