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incubator-nuttx/mm/iob/iob.h

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NET: Add generic I/O buffering logic
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/****************************************************************************
IOBs: Move from driver/iob to a better location in mm/iob
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* mm/iob/iob.h
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*
Move net/iob to drivers/iob so that the I/O buffering feature can be available to other drivers when networking is disabled.
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* Copyright (C) 2014, 2017 Gregory Nutt. All rights reserved.
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* 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.
*
****************************************************************************/
IOBs: Move from driver/iob to a better location in mm/iob
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#ifndef __MM_IOB_IOB_H
#define __MM_IOB_IOB_H 1
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/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
First cut at conversion of write-buffering to use I/O buffer chaings (IOBs)
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#include <semaphore.h>
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#include <debug.h>
First cut at conversion of write-buffering to use I/O buffer chaings (IOBs)
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IOBs: Move from driver/iob to a better location in mm/iob
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#include <nuttx/mm/iob.h>
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#ifdef CONFIG_MM_IOB
Eliminate some warnings
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Move net/iob to drivers/iob so that the I/O buffering feature can be available to other drivers when networking is disabled.
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/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
#if defined(CONFIG_DEBUG_FEATURES) && defined(CONFIG_IOB_DEBUG)
#ifdef CONFIG_CPP_HAVE_VARARGS
# define ioberr(format, ...) _err(format, ##__VA_ARGS__)
# define iobwarn(format, ...) _warn(format, ##__VA_ARGS__)
# define iobinfo(format, ...) _info(format, ##__VA_ARGS__)
#else
mm/: Remove dangling space at the end of lines.
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# define ioberr _err
# define iobwarn _warn
# define iobinfo _info
#endif
#else
#ifdef CONFIG_CPP_HAVE_VARARGS
# define ioberr(format, ...)
# define iobwarn(format, ...)
# define iobinfo(format, ...)
#else
mm/: Remove dangling space at the end of lines.
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Move net/iob to drivers/iob so that the I/O buffering feature can be available to other drivers when networking is disabled.
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# define ioberr (void)
# define iobwarn (void)
# define iobinfo (void)
#endif
#endif /* CONFIG_DEBUG_FEATURES && CONFIG_IOB_DEBUG */
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/****************************************************************************
* Public Data
****************************************************************************/
IOB: Add queue handling interfaces; improve lists
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/* A list of all free, unallocated I/O buffers */
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extern FAR struct iob_s *g_iob_freelist;
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There can be a failure in IOB allocation to some asynchronous behavior caused by the use of sem_post(). Consider this scenario: Task A holds an IOB.  There are no further IOBs.  The value of semcount is zero. Task B calls iob_alloc().  Since there are not IOBs, it calls sem_wait().  The v alue of semcount is now -1. Task A frees the IOB.  iob_free() adds the IOB to the free list and calls sem_post() this makes Task B ready to run and sets semcount to zero NOT 1.  There is one IOB in the free list and semcount is zero.  When Task B wakes up it would increment the sem_count back to the correct value. But an interrupt or another task runs occurs before Task B executes.  The interrupt or other tak takes the IOB off of the free list and decrements the semcount.  But since semcount is then < 0, this causes the assertion because that is an invalid state in the interrupt handler. So I think that the root cause is that there the asynchrony between incrementing the semcount. This change separates the list of IOBs: Currently there is only a free list of IOBs. The problem, I believe, is because of asynchronies due sem_post() post cause the semcount and the list content to become out of sync. This change adds a new 'committed' list: When there is a task waiting for an IOB, it will go into the committed list rather than the free list before the semaphore is posted. On the waiting side, when awakened from the semaphore wait, it will expect to find its IOB in the committed list, rather than free list. In this way, the content of the free list and the value of the semaphore count always remain in sync.
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/* A list of I/O buffers that are committed for allocation */
extern FAR struct iob_s *g_iob_committed;
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#if CONFIG_IOB_NCHAINS > 0
There can be a failure in IOB allocation to some asynchronous behavior caused by the use of sem_post(). Consider this scenario: Task A holds an IOB.  There are no further IOBs.  The value of semcount is zero. Task B calls iob_alloc().  Since there are not IOBs, it calls sem_wait().  The v alue of semcount is now -1. Task A frees the IOB.  iob_free() adds the IOB to the free list and calls sem_post() this makes Task B ready to run and sets semcount to zero NOT 1.  There is one IOB in the free list and semcount is zero.  When Task B wakes up it would increment the sem_count back to the correct value. But an interrupt or another task runs occurs before Task B executes.  The interrupt or other tak takes the IOB off of the free list and decrements the semcount.  But since semcount is then < 0, this causes the assertion because that is an invalid state in the interrupt handler. So I think that the root cause is that there the asynchrony between incrementing the semcount. This change separates the list of IOBs: Currently there is only a free list of IOBs. The problem, I believe, is because of asynchronies due sem_post() post cause the semcount and the list content to become out of sync. This change adds a new 'committed' list: When there is a task waiting for an IOB, it will go into the committed list rather than the free list before the semaphore is posted. On the waiting side, when awakened from the semaphore wait, it will expect to find its IOB in the committed list, rather than free list. In this way, the content of the free list and the value of the semaphore count always remain in sync.
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/* A list of all free, unallocated I/O buffer queue containers */
IOB: Add queue handling interfaces; improve lists
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extern FAR struct iob_qentry_s *g_iob_freeqlist;
There can be a failure in IOB allocation to some asynchronous behavior caused by the use of sem_post(). Consider this scenario: Task A holds an IOB.  There are no further IOBs.  The value of semcount is zero. Task B calls iob_alloc().  Since there are not IOBs, it calls sem_wait().  The v alue of semcount is now -1. Task A frees the IOB.  iob_free() adds the IOB to the free list and calls sem_post() this makes Task B ready to run and sets semcount to zero NOT 1.  There is one IOB in the free list and semcount is zero.  When Task B wakes up it would increment the sem_count back to the correct value. But an interrupt or another task runs occurs before Task B executes.  The interrupt or other tak takes the IOB off of the free list and decrements the semcount.  But since semcount is then < 0, this causes the assertion because that is an invalid state in the interrupt handler. So I think that the root cause is that there the asynchrony between incrementing the semcount. This change separates the list of IOBs: Currently there is only a free list of IOBs. The problem, I believe, is because of asynchronies due sem_post() post cause the semcount and the list content to become out of sync. This change adds a new 'committed' list: When there is a task waiting for an IOB, it will go into the committed list rather than the free list before the semaphore is posted. On the waiting side, when awakened from the semaphore wait, it will expect to find its IOB in the committed list, rather than free list. In this way, the content of the free list and the value of the semaphore count always remain in sync.
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/* A list of I/O buffer queue containers that are committed for allocation */
IOBs: Fix a typing error mm/iob/iob.h mm/iob/iob_initialize.c
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extern FAR struct iob_qentry_s *g_iob_qcommitted;
Add throttle support to the I/O buffer logic
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#endif
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/* Counting semaphores that tracks the number of free IOBs/qentries */
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extern sem_t g_iob_sem; /* Counts free I/O buffers */
#if CONFIG_IOB_THROTTLE > 0
extern sem_t g_throttle_sem; /* Counts available I/O buffers when throttled */
#endif
#if CONFIG_IOB_NCHAINS > 0
extern sem_t g_qentry_sem; /* Counts free I/O buffer queue containers */
#endif
First cut at conversion of write-buffering to use I/O buffer chaings (IOBs)
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NET: Add generic I/O buffering logic
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/****************************************************************************
* Public Function Prototypes
****************************************************************************/
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/****************************************************************************
* 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);
Networking: The are issues with the TCP write-ahead buffering if CONFIG_NET_NOINTS is enabled: There is a possibility of deadlocks in certain timing conditions. I have not seen this with the Tiva driver that I have been users but other people claim to see the issue on other platforms. Certainly it is a logic error: The network should never wait for TCP read-ahead buffering space to be available. It should drop the packets immediately. This was fixed by duplicating most of the IOB interfaces: The versions that waited are still present (like iob_alloc()), but now there are non-waiting verisons of the same interfaces (like iob_tryalloc()). The TCP read-ahead logic now uses only these non-waiting interfaces.
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/****************************************************************************
* 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);
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/****************************************************************************
* Name: iob_free_qentry
*
* Description:
* Free the I/O buffer chain container by returning it to the free list.
* The link to the next I/O buffer in the chain is return.
*
****************************************************************************/
FAR struct iob_qentry_s *iob_free_qentry(FAR struct iob_qentry_s *iobq);
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#endif /* CONFIG_MM_IOB */
#endif /* __MM_IOB_IOB_H */