/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/ /*** This file is part of systemd. Copyright 2010 Lennart Poettering systemd 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. systemd 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 systemd; If not, see <http://www.gnu.org/licenses/>. ***/ #include <stdlib.h> #include <stdbool.h> #include <errno.h> #include <string.h> #include <stdio.h> #include <limits.h> #include <sys/file.h> #include "util.h" #include "lockfile-util.h" #include "fileio.h" int make_lock_file(const char *p, int operation, LockFile *ret) { _cleanup_close_ int fd = -1; _cleanup_free_ char *t = NULL; int r; /* * We use UNPOSIX locks if they are available. They have nice * semantics, and are mostly compatible with NFS. However, * they are only available on new kernels. When we detect we * are running on an older kernel, then we fall back to good * old BSD locks. They also have nice semantics, but are * slightly problematic on NFS, where they are upgraded to * POSIX locks, even though locally they are orthogonal to * POSIX locks. */ t = strdup(p); if (!t) return -ENOMEM; for (;;) { struct flock fl = { .l_type = (operation & ~LOCK_NB) == LOCK_EX ? F_WRLCK : F_RDLCK, .l_whence = SEEK_SET, }; struct stat st; fd = open(p, O_CREAT|O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NOCTTY, 0600); if (fd < 0) return -errno; r = fcntl(fd, (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW, &fl); if (r < 0) { /* If the kernel is too old, use good old BSD locks */ if (errno == EINVAL) r = flock(fd, operation); if (r < 0) return errno == EAGAIN ? -EBUSY : -errno; } /* If we acquired the lock, let's check if the file * still exists in the file system. If not, then the * previous exclusive owner removed it and then closed * it. In such a case our acquired lock is worthless, * hence try again. */ r = fstat(fd, &st); if (r < 0) return -errno; if (st.st_nlink > 0) break; fd = safe_close(fd); } ret->path = t; ret->fd = fd; ret->operation = operation; fd = -1; t = NULL; return r; } int make_lock_file_for(const char *p, int operation, LockFile *ret) { const char *fn; char *t; assert(p); assert(ret); fn = basename(p); if (!filename_is_valid(fn)) return -EINVAL; t = newa(char, strlen(p) + 2 + 4 + 1); stpcpy(stpcpy(stpcpy(mempcpy(t, p, fn - p), ".#"), fn), ".lck"); return make_lock_file(t, operation, ret); } void release_lock_file(LockFile *f) { int r; if (!f) return; if (f->path) { /* If we are the exclusive owner we can safely delete * the lock file itself. If we are not the exclusive * owner, we can try becoming it. */ if (f->fd >= 0 && (f->operation & ~LOCK_NB) == LOCK_SH) { static const struct flock fl = { .l_type = F_WRLCK, .l_whence = SEEK_SET, }; r = fcntl(f->fd, F_OFD_SETLK, &fl); if (r < 0 && errno == EINVAL) r = flock(f->fd, LOCK_EX|LOCK_NB); if (r >= 0) f->operation = LOCK_EX|LOCK_NB; } if ((f->operation & ~LOCK_NB) == LOCK_EX) unlink_noerrno(f->path); f->path = mfree(f->path); } f->fd = safe_close(f->fd); f->operation = 0; }