/* Copyright (C) 2002-2017 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Ulrich Drepper <drepper@redhat.com>, 2002. 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 <http://www.gnu.org/licenses/>. */ #include <errno.h> #include <fcntl.h> #include <pthread.h> #include <search.h> #include <semaphore.h> #include <stdarg.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/mman.h> #include <sys/stat.h> #include "semaphoreP.h" #include <shm-directory.h> #include <futex-internal.h> #include <libc-lock.h> /* Comparison function for search of existing mapping. */ int attribute_hidden __sem_search (const void *a, const void *b) { const struct inuse_sem *as = (const struct inuse_sem *) a; const struct inuse_sem *bs = (const struct inuse_sem *) b; if (as->ino != bs->ino) /* Cannot return the difference the type is larger than int. */ return as->ino < bs->ino ? -1 : (as->ino == bs->ino ? 0 : 1); if (as->dev != bs->dev) /* Cannot return the difference the type is larger than int. */ return as->dev < bs->dev ? -1 : (as->dev == bs->dev ? 0 : 1); return strcmp (as->name, bs->name); } /* The search tree for existing mappings. */ void *__sem_mappings attribute_hidden; /* Lock to protect the search tree. */ int __sem_mappings_lock attribute_hidden = LLL_LOCK_INITIALIZER; /* Search for existing mapping and if possible add the one provided. */ static sem_t * check_add_mapping (const char *name, size_t namelen, int fd, sem_t *existing) { sem_t *result = SEM_FAILED; /* Get the information about the file. */ struct stat64 st; if (__fxstat64 (_STAT_VER, fd, &st) == 0) { /* Get the lock. */ lll_lock (__sem_mappings_lock, LLL_PRIVATE); /* Search for an existing mapping given the information we have. */ struct inuse_sem *fake; fake = (struct inuse_sem *) alloca (sizeof (*fake) + namelen); memcpy (fake->name, name, namelen); fake->dev = st.st_dev; fake->ino = st.st_ino; struct inuse_sem **foundp = __tfind (fake, &__sem_mappings, __sem_search); if (foundp != NULL) { /* There is already a mapping. Use it. */ result = (*foundp)->sem; ++(*foundp)->refcnt; } else { /* We haven't found a mapping. Install ione. */ struct inuse_sem *newp; newp = (struct inuse_sem *) malloc (sizeof (*newp) + namelen); if (newp != NULL) { /* If the caller hasn't provided any map it now. */ if (existing == SEM_FAILED) existing = (sem_t *) mmap (NULL, sizeof (sem_t), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); newp->dev = st.st_dev; newp->ino = st.st_ino; newp->refcnt = 1; newp->sem = existing; memcpy (newp->name, name, namelen); /* Insert the new value. */ if (existing != MAP_FAILED && __tsearch (newp, &__sem_mappings, __sem_search) != NULL) /* Successful. */ result = existing; else /* Something went wrong while inserting the new value. We fail completely. */ free (newp); } } /* Release the lock. */ lll_unlock (__sem_mappings_lock, LLL_PRIVATE); } if (result != existing && existing != SEM_FAILED && existing != MAP_FAILED) { /* Do not disturb errno. */ int save = errno; munmap (existing, sizeof (sem_t)); errno = save; } return result; } 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; } /* Create the name of the final file in local variable SHM_NAME. */ SHM_GET_NAME (EINVAL, SEM_FAILED, SEM_SHM_PREFIX); /* 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 = __libc_open (shm_name, (oflag & ~(O_CREAT|O_ACCMODE)) | O_NOFOLLOW | O_RDWR); 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 = check_add_mapping (name, namelen, 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. */ char *tmpfname; 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; #if __HAVE_64B_ATOMICS sem.newsem.data = value; #else sem.newsem.value = value << SEM_VALUE_SHIFT; /* pad is used as a mutex on pre-v9 sparc and ignored otherwise. */ sem.newsem.pad = 0; sem.newsem.nwaiters = 0; #endif /* This always is a shared semaphore. */ sem.newsem.private = FUTEX_SHARED; /* Initialize the remaining bytes as well. */ memset ((char *) &sem.initsem + sizeof (struct new_sem), '\0', sizeof (sem_t) - sizeof (struct new_sem)); tmpfname = __alloca (shm_dirlen + sizeof SEM_SHM_PREFIX + 6); char *xxxxxx = __mempcpy (tmpfname, shm_dir, shm_dirlen); int retries = 0; #define NRETRIES 50 while (1) { /* Add the suffix for mktemp. */ strcpy (xxxxxx, "XXXXXX"); /* 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 = __libc_open (tmpfname, O_RDWR | O_CREAT | O_EXCL, mode); if (fd == -1) { if (errno == EEXIST) { if (++retries < NRETRIES) continue; __set_errno (EAGAIN); } result = SEM_FAILED; goto out; } /* We got a file. */ break; } if (TEMP_FAILURE_RETRY (__libc_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, shm_name) != 0) { /* Undo the mapping. */ (void) 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. */ (void) unlink (tmpfname); /* Close the file. */ (void) __libc_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 = check_add_mapping (name, namelen, fd, result); } /* Now remove the temporary name. This should never fail. If it fails we leak a file name. Better fix the kernel. */ (void) 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; __libc_close (fd); errno = save; } out: #ifdef __libc_ptf_call __libc_ptf_call (__pthread_setcancelstate, (state, NULL), 0); #endif return result; }