/* Copyright (c) 2003-2004, Roger Dingledine * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson. * Copyright (c) 2007-2018, The Tor Project, Inc. */ /* See LICENSE for licensing information */ /** * \file lockfile.c * * \brief Implements lock files to prevent two Tor processes from using the * same data directory at the same time. **/ #include "orconfig.h" #include "lib/fs/files.h" #include "lib/fs/lockfile.h" #include "lib/log/log.h" #include "lib/log/util_bug.h" #include "lib/malloc/malloc.h" #ifdef HAVE_SYS_FILE_H #include #endif #ifdef HAVE_FCNTL_H #include #endif #ifdef HAVE_UNISTD_H #include #endif #ifdef _WIN32 #include #include #endif #include #include /** Represents a lockfile on which we hold the lock. */ struct tor_lockfile_t { /** Name of the file */ char *filename; /** File descriptor used to hold the file open */ int fd; }; /** Try to get a lock on the lockfile filename, creating it as * necessary. If someone else has the lock and blocking is true, * wait until the lock is available. Otherwise return immediately whether * we succeeded or not. * * Set *locked_out to true if somebody else had the lock, and to false * otherwise. * * Return a tor_lockfile_t on success, NULL on failure. * * (Implementation note: because we need to fall back to fcntl on some * platforms, these locks are per-process, not per-thread. If you want * to do in-process locking, use tor_mutex_t like a normal person. * On Windows, when blocking is true, the maximum time that * is actually waited is 10 seconds, after which NULL is returned * and locked_out is set to 1.) */ tor_lockfile_t * tor_lockfile_lock(const char *filename, int blocking, int *locked_out) { tor_lockfile_t *result; int fd; *locked_out = 0; log_info(LD_FS, "Locking \"%s\"", filename); fd = tor_open_cloexec(filename, O_RDWR|O_CREAT|O_TRUNC, 0600); if (fd < 0) { log_warn(LD_FS,"Couldn't open \"%s\" for locking: %s", filename, strerror(errno)); return NULL; } #ifdef _WIN32 _lseek(fd, 0, SEEK_SET); if (_locking(fd, blocking ? _LK_LOCK : _LK_NBLCK, 1) < 0) { if (errno != EACCES && errno != EDEADLOCK) log_warn(LD_FS,"Couldn't lock \"%s\": %s", filename, strerror(errno)); else *locked_out = 1; close(fd); return NULL; } #elif defined(HAVE_FLOCK) if (flock(fd, LOCK_EX|(blocking ? 0 : LOCK_NB)) < 0) { if (errno != EWOULDBLOCK) log_warn(LD_FS,"Couldn't lock \"%s\": %s", filename, strerror(errno)); else *locked_out = 1; close(fd); return NULL; } #else { struct flock lock; memset(&lock, 0, sizeof(lock)); lock.l_type = F_WRLCK; lock.l_whence = SEEK_SET; if (fcntl(fd, blocking ? F_SETLKW : F_SETLK, &lock) < 0) { if (errno != EACCES && errno != EAGAIN) log_warn(LD_FS, "Couldn't lock \"%s\": %s", filename, strerror(errno)); else *locked_out = 1; close(fd); return NULL; } } #endif /* defined(_WIN32) || ... */ result = tor_malloc(sizeof(tor_lockfile_t)); result->filename = tor_strdup(filename); result->fd = fd; return result; } /** Release the lock held as lockfile. */ void tor_lockfile_unlock(tor_lockfile_t *lockfile) { tor_assert(lockfile); log_info(LD_FS, "Unlocking \"%s\"", lockfile->filename); #ifdef _WIN32 _lseek(lockfile->fd, 0, SEEK_SET); if (_locking(lockfile->fd, _LK_UNLCK, 1) < 0) { log_warn(LD_FS,"Error unlocking \"%s\": %s", lockfile->filename, strerror(errno)); } #elif defined(HAVE_FLOCK) if (flock(lockfile->fd, LOCK_UN) < 0) { log_warn(LD_FS, "Error unlocking \"%s\": %s", lockfile->filename, strerror(errno)); } #else /* Closing the lockfile is sufficient. */ #endif /* defined(_WIN32) || ... */ close(lockfile->fd); lockfile->fd = -1; tor_free(lockfile->filename); tor_free(lockfile); }