diff options
Diffstat (limited to 'src/shared/lockfile-util.c')
| -rw-r--r-- | src/shared/lockfile-util.c | 154 |
1 files changed, 154 insertions, 0 deletions
diff --git a/src/shared/lockfile-util.c b/src/shared/lockfile-util.c new file mode 100644 index 0000000000..05e16d1caa --- /dev/null +++ b/src/shared/lockfile-util.c @@ -0,0 +1,154 @@ +/*-*- 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); + + free(f->path); + f->path = NULL; + } + + f->fd = safe_close(f->fd); + f->operation = 0; +} |