/****************************************************************************
* net/netdev_sem.c
*
* Copyright (C) 2012 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>
#if defined(CONFIG_NET) && CONFIG_NSOCKET_DESCRIPTORS > 0
#include <sys/types.h>
#include <unistd.h>
#include <semaphore.h>
#include <assert.h>
#include <errno.h>
#include "net_internal.h"
/****************************************************************************
* Definitions
****************************************************************************/
#define NO_HOLDER (pid_t)-1
/****************************************************************************
* Priviate Types
****************************************************************************/
/* There is at least on context in which recursive semaphores are required:
* When netdev_foreach is used with a telnet client, we will deadlock if we
* do not provide this capability.
*/
struct netdev_sem_s
{
sem_t sem;
pid_t holder;
unsigned int count;
};
/****************************************************************************
* Private Data
****************************************************************************/
/****************************************************************************
* Public Data
****************************************************************************/
static struct netdev_sem_s g_devlock;
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Global Functions
****************************************************************************/
/****************************************************************************
* Function: netdev_seminit
*
* Description:
* Initialize the network device semaphore.
*
****************************************************************************/
void netdev_seminit(void)
{
sem_init(&g_devlock.sem, 0, 1);
g_devlock.holder = NO_HOLDER;
g_devlock.count = 0;
}
/****************************************************************************
* Function: netdev_semtake
*
* Description:
* Get exclusive access to the network device list.
*
****************************************************************************/
void netdev_semtake(void)
{
pid_t me = getpid();
/* Does this thread already hold the semaphore? */
if (g_devlock.holder == me)
{
/* Yes.. just increment the reference count */
g_devlock.count++;
}
else
{
/* No.. take the semaphore (perhaps waiting) */
while (uip_lockedwait(&g_devlock.sem) != 0)
{
/* The only case that an error should occur here is if
* the wait was awakened by a signal.
*/
ASSERT(errno == EINTR);
}
/* Now this thread holds the semaphore */
g_devlock.holder = me;
g_devlock.count = 1;
}
}
/****************************************************************************
* Function: netdev_semtake
*
* Description:
* Release exclusive access to the network device list
*
****************************************************************************/
void netdev_semgive(void)
{
DEBUGASSERT(g_devlock.holder == getpid() && g_devlock.count > 0);
/* If the count would go to zero, then release the semaphore */
if (g_devlock.count == 1)
{
/* We no longer hold the semaphore */
g_devlock.holder = NO_HOLDER;
g_devlock.count = 0;
sem_post(&g_devlock.sem);
}
else
{
/* We still hold the semaphore. Just decrement the count */
g_devlock.count--;
}
}
#endif /* CONFIG_NET && CONFIG_NSOCKET_DESCRIPTORS */
