123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254 |
- /****************************************************************************
- * fs/semaphore/sem_open.c
- *
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership. The
- * ASF licenses this file to you under the Apache License, Version 2.0 (the
- * "License"); you may not use this file except in compliance with the
- * License. You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
- * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
- * License for the specific language governing permissions and limitations
- * under the License.
- *
- ****************************************************************************/
- /****************************************************************************
- * Included Files
- ****************************************************************************/
- #include <nuttx/config.h>
- #include <stdint.h>
- #include <stdbool.h>
- #include <stdarg.h>
- #include <stdio.h>
- #include <fcntl.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
- /****************************************************************************
- * 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()).
- *
- * Input 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.
- *
- * Returned Value:
- * A pointer to sem_t or SEM_FAILED if unsuccessful.
- *
- * Assumptions:
- *
- ****************************************************************************/
- FAR sem_t *sem_open (FAR const char *name, int oflags, ...)
- {
- FAR struct inode *inode;
- FAR struct nsem_inode_s *nsem;
- FAR sem_t *sem = (FAR sem_t *)ERROR;
- struct inode_search_s desc;
- char fullpath[MAX_SEMPATH];
- mode_t mode;
- unsigned value;
- int errcode;
- int ret;
- /* Make sure that a non-NULL name is supplied */
- DEBUGASSERT(name != NULL);
- /* 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. In this case, inode_find()
- * will have incremented the reference count on the inode.
- */
- SETUP_SEARCH(&desc, fullpath, false);
- ret = inode_find(&desc);
- if (ret >= 0)
- {
- /* Something exists at this path. Get the search results */
- inode = desc.node;
- DEBUGASSERT(inode != NULL);
- /* 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. The new
- * inode will be created with a reference count of zero.
- */
- ret = inode_semtake();
- if (ret < 0)
- {
- errcode = -ret;
- goto errout_with_lock;
- }
- 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 */
- nxsem_init(&nsem->ns_sem, 0, value);
- /* Return a reference to the semaphore */
- sem = &nsem->ns_sem;
- }
- RELEASE_SEARCH(&desc);
- sched_unlock();
- return sem;
- errout_with_inode:
- inode_release(inode);
- errout_with_lock:
- RELEASE_SEARCH(&desc);
- set_errno(errcode);
- sched_unlock();
- return SEM_FAILED;
- }
- #endif /* CONFIG_FS_NAMED_SEMAPHORES */
|