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incubator-nuttx/fs/semaphore/sem_open.c

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/****************************************************************************
* fs/semaphore/sem_open.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 <stdint.h>
#include <stdarg.h>
#include <stdio.h>
#include <fcntl.h>
#include <semaphore.h>
#include <string.h>
#include <sched.h>
#include <errno.h>
#include <nuttx/kmalloc.h>
#include <nuttx/semaphore.h>
#include <nuttx/fs/fs.h>
#include "inode/inode.h"
#include "semaphore/semaphore.h"
#ifdef CONFIG_FS_NAMED_SEMAPHORES
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Private Type Declarations
****************************************************************************/
/****************************************************************************
* Global Variables
****************************************************************************/
/****************************************************************************
* Private Variables
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: 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
* oflags - Semaphore creation options. This may either or both of the
* following bit settings.
* oflags = 0: Connect to the semaphore only if it already exists.
* oflags = O_CREAT: Connect to the semaphore if it exists, otherwise
* create the semaphore.
* oflags = 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 (FAR const char *name, int oflags, ...)
{
FAR struct inode *inode;
FAR const char *relpath = NULL;
mode_t mode;
FAR struct nsem_inode_s *nsem;
FAR sem_t *sem = (FAR sem_t*)ERROR;
char fullpath[MAX_SEMPATH];
unsigned value;
int errcode;
int ret;
/* 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();
/* Get the full path to the semaphore */
snprintf(fullpath, MAX_SEMPATH, CONFIG_FS_NAMED_SEMPATH "/%s", name);
/* Get the inode for this semaphore. This should succeed if the semaphore
* has already been created.
*/
inode = inode_find(fullpath, &relpath);
if (inode)
{
/* It exists. Verify that the inode is a semaphore */
if (!INODE_IS_NAMEDSEM(inode))
{
errcode = ENXIO;
goto errout_with_inode;
}
/* It exists and is a semaphore. Check if the caller wanted to
* create a new semaphore with this name.
*/
if ((oflags & (O_CREAT|O_EXCL)) == (O_CREAT|O_EXCL))
{
errcode = EEXIST;
goto errout_with_inode;
}
/* Return a reference to the semaphore, retaining the reference
* count on the inode.
*/
sem = &inode->u.i_nsem->ns_sem;
}
else
{
va_list ap;
/* The semaphore does not exists. Were we asked to create it? */
if ((oflags & O_CREAT) == 0)
{
/* The semaphore does not exist and O_CREAT is not set */
errcode = ENOENT;
goto errout_with_lock;
}
/* Create the semaphore. First we have to extract the additional
* parameters from the variable argument list.
* REVISIT: Mode parameter is not currently used.
*/
va_start(ap, oflags);
mode = va_arg(ap, mode_t);
value = va_arg(ap, unsigned);
va_end(ap);
UNUSED(mode);
/* Check the semaphore value */
if (value > SEM_VALUE_MAX)
{
errcode = EINVAL;
goto errout_with_lock;
}
/* Create an inode in the pseudo-filesystem at this path */
inode_semtake();
ret = inode_reserve(fullpath, &inode);
inode_semgive();
if (ret < 0)
{
errcode = -ret;
goto errout_with_lock;
}
/* Allocate the semaphore structure (using the appropriate allocator
* for the group)
*/
nsem = group_malloc(NULL, sizeof(struct nsem_inode_s));
if (!nsem)
{
errcode = ENOMEM;
goto errout_with_inode;
}
/* Link to the inode */
inode->u.i_nsem = nsem;
nsem->ns_inode = inode;
/* Initialize the inode */
INODE_SET_NAMEDSEM(inode);
inode->i_crefs = 1;
/* Initialize the semaphore */
sem_init(&nsem->ns_sem, 0, value);
/* Return a reference to the semaphore */
sem = &nsem->ns_sem;
}
sched_unlock();
}
return sem;
errout_with_inode:
inode_release(inode);
errout_with_lock:
set_errno(errcode);
sched_unlock();
return (FAR sem_t *)ERROR;
}
#endif /* CONFIG_FS_NAMED_SEMAPHORES */
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