/****************************************************************************
* mm/iob/iob_alloc.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 <semaphore.h>
#include <assert.h>
#include <errno.h>
#include <nuttx/irq.h>
#include <nuttx/arch.h>
#include <nuttx/sched.h>
#include <nuttx/mm/iob.h>
#include "iob.h"
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: iob_alloc_committed
*
* Description:
* Allocate an I/O buffer by taking the buffer at the head of the committed
* list.
*
****************************************************************************/
static FAR struct iob_s *iob_alloc_committed(enum iob_user_e consumerid)
{
FAR struct iob_s *iob = 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 */
iob = g_iob_committed;
if (iob != NULL)
{
/* Remove the I/O buffer from the committed list */
g_iob_committed = iob->io_flink;
/* 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 */
#if !defined(CONFIG_DISABLE_MOUNTPOINT) && defined(CONFIG_FS_PROCFS) && \
defined(CONFIG_MM_IOB) && !defined(CONFIG_FS_PROCFS_EXCLUDE_IOBINFO)
iob_stats_onalloc(consumerid);
#endif
}
leave_critical_section(flags);
return iob;
}
/****************************************************************************
* 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,
enum iob_user_e consumerid)
{
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();
/* Try to get an I/O buffer. If successful, the semaphore count will be
* decremented atomically.
*/
iob = iob_tryalloc(throttled, consumerid);
while (ret == OK && iob == 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 to be released and placed in the committed
* list.
*/
ret = nxsem_wait(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 are 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 was
* freed and we hold a count for one IOB.
*/
iob = iob_alloc_committed(consumerid);
if (iob == NULL)
{
/* 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(sem);
iob = iob_tryalloc(throttled, consumerid);
}
/* REVISIT: I think this logic should be moved inside of
* iob_alloc_committed, so that it can exist inside of the critical
* section along with all other sem count changes.
*/
#if CONFIG_IOB_THROTTLE > 0
else
{
if (throttled)
{
g_iob_sem.semcount--;
}
else
{
g_throttle_sem.semcount--;
}
}
#endif
}
}
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, enum iob_user_e consumerid)
{
/* 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(throttled, consumerid);
}
else
{
/* Then allocate an I/O buffer, waiting as necessary */
return iob_allocwait(throttled, consumerid);
}
}
/****************************************************************************
* 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, enum iob_user_e consumerid)
{
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 != NULL)
{
/* 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 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_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
#if !defined(CONFIG_DISABLE_MOUNTPOINT) && defined(CONFIG_FS_PROCFS) && \
defined(CONFIG_MM_IOB) && !defined(CONFIG_FS_PROCFS_EXCLUDE_IOBINFO)
iob_stats_onalloc(consumerid);
#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;
}