/**************************************************************************** * drivers/iob/iob_alloc.c * * Copyright (C) 2014, 2016 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" /**************************************************************************** * Private Functions ****************************************************************************/ /**************************************************************************** * Name: iob_allocwait * * Description: * Allocate an I/O buffer, waiting if necessary. This function cannot be * called from any interrupt level logic. * ****************************************************************************/ static FAR struct iob_s *iob_allocwait(bool throttled) { FAR struct iob_s *iob; irqstate_t flags; FAR sem_t *sem; int ret = OK; #if CONFIG_IOB_THROTTLE > 0 /* Select the semaphore count to check. */ sem = (throttled ? &g_throttle_sem : &g_iob_sem); #else sem = &g_iob_sem; #endif /* The following must be atomic; interrupt must be disabled so that there * is no conflict with interrupt level I/O buffer 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(); do { /* Try to get an I/O buffer. If successful, the semaphore count * will be decremented atomically. */ iob = iob_tryalloc(throttled); if (!iob) { /* 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 to be released when the semaphore * count will be incremented. */ ret = sem_wait(sem); if (ret < 0) { int errcode = get_errno(); /* 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 (errcode == EINTR) { /* Force a success indication so that we will continue * looping. */ ret = 0; } else { /* Stop the loop and return a error */ DEBUGASSERT(errcode > 0); ret = -errcode; } } else { /* When we wake up from wait successfully, an I/O buffer was * returned to the free list. However, if there are concurrent * allocations from interrupt handling, then I suspect that * there is a race condition. But no harm, we will just wait * again in that case. * * 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. * * TODO: Consider a design modification to permit us to * complete the allocation without losing our count. */ sem_post(sem); } } } while (ret == OK && iob == NULL); leave_critical_section(flags); return iob; } /**************************************************************************** * Public Functions ****************************************************************************/ /**************************************************************************** * Name: iob_alloc * * Description: * Allocate an I/O buffer by taking the buffer at the head of the free list. * ****************************************************************************/ FAR struct iob_s *iob_alloc(bool throttled) { /* Were we called from the interrupt level? */ if (up_interrupt_context()) { /* Yes, then try to allocate an I/O buffer without waiting */ return iob_tryalloc(throttled); } else { /* Then allocate an I/O buffer, waiting as necessary */ return iob_allocwait(throttled); } } /**************************************************************************** * Name: iob_tryalloc * * Description: * Try to allocate an I/O buffer by taking the buffer at the head of the * free list without waiting for a buffer to become free. * ****************************************************************************/ FAR struct iob_s *iob_tryalloc(bool throttled) { FAR struct iob_s *iob; irqstate_t flags; #if CONFIG_IOB_THROTTLE > 0 FAR sem_t *sem; #endif #if CONFIG_IOB_THROTTLE > 0 /* Select the semaphore count to check. */ sem = (throttled ? &g_throttle_sem : &g_iob_sem); #endif /* 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(); #if CONFIG_IOB_THROTTLE > 0 /* If there are free I/O buffers for this allocation */ if (sem->semcount > 0) #endif { /* Take the I/O buffer from the head of the free list */ iob = g_iob_freelist; if (iob) { /* Remove the I/O buffer from the free list and decrement the * counting semaphore(s) that tracks the number of available * IOBs. */ g_iob_freelist = iob->io_flink; /* Take a semaphore count. Note that we cannot do this in * in the orthodox way by calling sem_wait() or sem_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_iob_sem.semcount--; DEBUGASSERT(g_iob_sem.semcount >= 0); #if CONFIG_IOB_THROTTLE > 0 /* The throttle semaphore is a little more complicated because * it can be negative! Decrementing is still safe, however. */ g_throttle_sem.semcount--; DEBUGASSERT(g_throttle_sem.semcount >= -CONFIG_IOB_THROTTLE); #endif leave_critical_section(flags); /* Put the I/O buffer in a known state */ iob->io_flink = NULL; /* Not in a chain */ iob->io_len = 0; /* Length of the data in the entry */ iob->io_offset = 0; /* Offset to the beginning of data */ iob->io_pktlen = 0; /* Total length of the packet */ return iob; } } leave_critical_section(flags); return NULL; }