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/* Copyright (C) 2002-2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <fcntl.h>
#include <semaphore.h>
#include <stdarg.h>
#include <unistd.h>
#include <sys/mman.h>
#include "semaphoreP.h"
#include <shm-directory.h>
#include <sem_routines.h>
#include <futex-internal.h>
#include <libc-lock.h>
#if !PTHREAD_IN_LIBC
/* The private names are not exported from libc. */
# define __link link
# define __unlink unlink
#endif
#define SEM_OPEN_FLAGS (O_RDWR | O_NOFOLLOW | O_CLOEXEC)
sem_t *
__sem_open (const char *name, int oflag, ...)
{
int fd;
sem_t *result;
/* Check that shared futexes are supported. */
int err = futex_supports_pshared (PTHREAD_PROCESS_SHARED);
if (err != 0)
{
__set_errno (err);
return SEM_FAILED;
}
struct shmdir_name dirname;
int ret = __shm_get_name (&dirname, name, true);
if (ret != 0)
{
__set_errno (ret);
return SEM_FAILED;
}
/* Disable asynchronous cancellation. */
#ifdef __libc_ptf_call
int state;
__libc_ptf_call (__pthread_setcancelstate,
(PTHREAD_CANCEL_DISABLE, &state), 0);
#endif
/* If the semaphore object has to exist simply open it. */
if ((oflag & O_CREAT) == 0 || (oflag & O_EXCL) == 0)
{
try_again:
fd = __open (dirname.name, (oflag & O_EXCL) | SEM_OPEN_FLAGS);
if (fd == -1)
{
/* If we are supposed to create the file try this next. */
if ((oflag & O_CREAT) != 0 && errno == ENOENT)
goto try_create;
/* Return. errno is already set. */
}
else
/* Check whether we already have this semaphore mapped and
create one if necessary. */
result = __sem_check_add_mapping (name, fd, SEM_FAILED);
}
else
{
/* We have to open a temporary file first since it must have the
correct form before we can start using it. */
mode_t mode;
unsigned int value;
va_list ap;
try_create:
va_start (ap, oflag);
mode = va_arg (ap, mode_t);
value = va_arg (ap, unsigned int);
va_end (ap);
if (value > SEM_VALUE_MAX)
{
__set_errno (EINVAL);
result = SEM_FAILED;
goto out;
}
/* Create the initial file content. */
union
{
sem_t initsem;
struct new_sem newsem;
} sem;
__new_sem_open_init (&sem.newsem, value);
/* Initialize the remaining bytes as well. */
memset ((char *) &sem.initsem + sizeof (struct new_sem), '\0',
sizeof (sem_t) - sizeof (struct new_sem));
char tmpfname[] = SHMDIR "sem.XXXXXX";
int retries = 0;
#define NRETRIES 50
while (1)
{
/* We really want to use mktemp here. We cannot use mkstemp
since the file must be opened with a specific mode. The
mode cannot later be set since then we cannot apply the
file create mask. */
if (__mktemp (tmpfname) == NULL)
{
result = SEM_FAILED;
goto out;
}
/* Open the file. Make sure we do not overwrite anything. */
fd = __open (tmpfname, O_CREAT | O_EXCL | SEM_OPEN_FLAGS, mode);
if (fd == -1)
{
if (errno == EEXIST)
{
if (++retries < NRETRIES)
{
/* Restore the six placeholder bytes before the
null terminator before the next attempt. */
memcpy (tmpfname + sizeof (tmpfname) - 7, "XXXXXX", 6);
continue;
}
__set_errno (EAGAIN);
}
result = SEM_FAILED;
goto out;
}
/* We got a file. */
break;
}
if (TEMP_FAILURE_RETRY (write (fd, &sem.initsem, sizeof (sem_t)))
== sizeof (sem_t)
/* Map the sem_t structure from the file. */
&& (result = (sem_t *) __mmap (NULL, sizeof (sem_t),
PROT_READ | PROT_WRITE, MAP_SHARED,
fd, 0)) != MAP_FAILED)
{
/* Create the file. Don't overwrite an existing file. */
if (__link (tmpfname, dirname.name) != 0)
{
/* Undo the mapping. */
__munmap (result, sizeof (sem_t));
/* Reinitialize 'result'. */
result = SEM_FAILED;
/* This failed. If O_EXCL is not set and the problem was
that the file exists, try again. */
if ((oflag & O_EXCL) == 0 && errno == EEXIST)
{
/* Remove the file. */
__unlink (tmpfname);
/* Close the file. */
__close (fd);
goto try_again;
}
}
else
/* Insert the mapping into the search tree. This also
determines whether another thread sneaked by and already
added such a mapping despite the fact that we created it. */
result = __sem_check_add_mapping (name, fd, result);
}
/* Now remove the temporary name. This should never fail. If
it fails we leak a file name. Better fix the kernel. */
__unlink (tmpfname);
}
/* Map the mmap error to the error we need. */
if (MAP_FAILED != (void *) SEM_FAILED && result == MAP_FAILED)
result = SEM_FAILED;
/* We don't need the file descriptor anymore. */
if (fd != -1)
{
/* Do not disturb errno. */
int save = errno;
__close (fd);
errno = save;
}
out:
#ifdef __libc_ptf_call
__libc_ptf_call (__pthread_setcancelstate, (state, NULL), 0);
#endif
return result;
}
#if PTHREAD_IN_LIBC
versioned_symbol (libc, __sem_open, sem_open, GLIBC_2_34);
# if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_1_1, GLIBC_2_34)
compat_symbol (libpthread, __sem_open, sem_open, GLIBC_2_1_1);
# endif
#else /* !PTHREAD_IN_LIBC */
strong_alias (__sem_open, sem_open)
#endif
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