/************************************************************
* sem_open.c
*
* Copyright (C) 2007 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
*
* 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 Gregory Nutt 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 <sys/types.h>
#include <stdarg.h>
#include <limits.h>
#include <fcntl.h>
#include <string.h>
#include <semaphore.h>
#include <errno.h>
#include <nuttx/kmalloc.h>
#include "sem_internal.h"
/************************************************************
* Compilation Switches
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/************************************************************
* Definitions
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/************************************************************
* Private Type Declarations
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/************************************************************
* Global Variables
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/************************************************************
* Private Variables
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/************************************************************
* Private Functions
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/************************************************************
* Public Functions
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/************************************************************
* Function: sem_open
*
* Description:
* This function establishes a connection between named
* semaphores and a task. Following a call to sem_open()
* with the semaphore name, the task may reference the
* semaphore associated with name using the address
* returned by this call. The semaphore may be used in
* subsequent calls to sem_wait(), sem_trywait(), and
* sem_post(). The semaphore remains usable until the
* semaphore is closed by a successful call to sem_close().
*
* If a task makes multiple calls to sem_open() with the
* same name, then the same semaphore address is returned
* (provided there have been no calls to sem_unlink()).
*
* Parameters:
* name - Semaphore name
* oflag - Semaphore creation options. This may either
* or both of the following bit settings.
* oflag = 0: Connect to the semaphore only if it
* already exists.
* oflag = O_CREAT: Connect to the semaphore if it
* exists, otherwise create the semaphore.
* oflag = O_CREAT|O_EXCL: Create a new semaphore
* unless one of this name already exists.
* Optional parameters. When the O_CREAT flag is specified,
* two optional parameters are expected:
* 1. mode_t mode (ignored), and
* 2. unsigned int value. This initial value of the semaphore.
* valid initial values of the semaphore must be less than
* or equal to SEM_VALUE_MAX.
*
* Return Value:
* A pointer to sem_t or -1 (ERROR) if unsuccessful.
*
* Assumptions:
*
************************************************************/
FAR sem_t *sem_open (const char *name, int oflag, ...)
{
int namelen;
FAR nsem_t *psem;
FAR sem_t *sem = (FAR sem_t*)ERROR;
va_list arg; /* Points to each un-named argument */
mode_t mode; /* Creation mode parameter (ignored) */
unsigned int value; /* Semaphore value parameter */
/* Make sure that a non-NULL name is supplied */
if (name)
{
/* The POSIX specification requires that the "check for the
* existence of a semaphore and the creation of the semaphore
* if it does not exist shall be atomic with respect to other
* processes executing sem_open()..." A simple sched_lock()
* should be sufficient to meet this requirement.
*/
sched_lock();
namelen = strlen(name);
if (namelen > 0)
{
/* See if the semaphore already exists */
psem = sem_findnamed(name);
if (psem)
{
/* It does. Check if the caller wanted to created
* a new semahore with this name.
*/
if (!(oflag & O_CREAT) || !(oflag & O_EXCL))
{
/* Allow a new connection to the semaphore */
psem->nconnect++;
sem = &psem->sem;
}
}
/* It doesn't exist. Should we create one? */
else if ((oflag & O_CREAT) != 0)
{
/* Set up to get the optional arguments needed to create
* a message queue.
*/
va_start(arg, oflag);
mode = va_arg(arg, mode_t);
value = va_arg(arg, unsigned int);
/* Verify that a legal initial value was selected. */
if (value <= SEM_VALUE_MAX)
{
/* Allocate memory for the new semaphore */
psem = (FAR nsem_t*)kmalloc((sizeof(nsem_t) + namelen + 1));
if (psem)
{
/* Initialize the named semaphore */
sem = &psem->sem;
sem_init(sem, 0, value);
psem->nconnect = 1;
psem->unlinked = FALSE;
psem->name = (FAR char*)psem + sizeof(nsem_t);
strcpy(psem->name, name);
/* Add the new semaphore to the list of named
* semaphores
*/
dq_addfirst((FAR dq_entry_t*)psem, &g_nsems);
}
/* Clean-up variable argument stuff */
va_end(arg);
}
}
}
sched_unlock();
}
return sem;
}
