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/****************************************************************************
* net/iob/iob_alloc.c
*
* Copyright (C) 2014 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 <nuttx/arch.h>
#include <nuttx/net/iob.h>
#include "iob.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Private Types
****************************************************************************/
/****************************************************************************
* Private Data
****************************************************************************/
/****************************************************************************
* Public Data
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: iob_tryalloc
*
* Description:
* Try to allocate an I/O buffer by taking the buffer at the head of the
* free list.
*
****************************************************************************/
static FAR struct iob_s *iob_tryalloc(void)
{
FAR struct iob_s *iob;
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 = irqsave();
iob = g_iob_freelist;
if (iob)
{
/* Remove the I/O buffer from the free list and decrement the counting
* semaphore that tracks the number of free IOBs.
*/
g_iob_freelist = iob->io_flink;
DEBUGVERIFY(sem_trywait(&g_iob_sem));
irqrestore(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;
}
irqrestore(flags);
return NULL;
}
/****************************************************************************
* 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(void)
{
FAR struct iob_s *iob;
irqstate_t flags;
int ret;
/* 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 = irqsave();
do
{
/* Try to get an I/O buffer. If successful, the semaphore count
* will be decremented atomically.
*/
iob = iob_tryalloc();
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(&g_iob_sem);
/* When we wake up from wait, 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.
*/
}
}
while (ret == OK && !iob);
irqrestore(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(void)
{
/* 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();
}
else
{
/* Then allocate an I/O buffer, waiting as necessary */
return iob_allocwait();
}
}
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