1 /* Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira, Inc.
3 * Licensed under the Apache License, Version 2.0 (the "License");
4 * you may not use this file except in compliance with the License.
5 * You may obtain a copy of the License at:
7 * http://www.apache.org/licenses/LICENSE-2.0
9 * Unless required by applicable law or agreed to in writing, software
10 * distributed under the License is distributed on an "AS IS" BASIS,
11 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 * See the License for the specific language governing permissions and
13 * limitations under the License.
34 VLOG_DEFINE_THIS_MODULE(lockfile);
36 COVERAGE_DEFINE(lockfile_lock);
37 COVERAGE_DEFINE(lockfile_timeout);
38 COVERAGE_DEFINE(lockfile_error);
39 COVERAGE_DEFINE(lockfile_unlock);
42 struct hmap_node hmap_node;
51 * We have to do this stupid dance because POSIX says that closing *any* file
52 * descriptor for a file on which a process holds a lock drops *all* locks on
53 * that file. That means that we can't afford to open a lockfile more than
55 static struct hmap lock_table = HMAP_INITIALIZER(&lock_table);
57 static void lockfile_unhash(struct lockfile *);
58 static int lockfile_try_lock(const char *name, bool block,
59 struct lockfile **lockfilep);
61 /* Returns the name of the lockfile that would be created for locking a file
62 * named 'filename_'. The caller is responsible for freeing the returned name,
63 * with free(), when it is no longer needed. */
65 lockfile_name(const char *filename_)
71 /* If 'filename_' is a symlink, base the name of the lockfile on the
72 * symlink's target rather than the name of the symlink. That way, if a
73 * file is symlinked, but there is no symlink for its lockfile, then there
74 * is only a single lockfile for both the source and the target of the
75 * symlink, not one for each. */
76 filename = follow_symlinks(filename_);
77 slash = strrchr(filename, '/');
79 ? xasprintf("%.*s/.%s.~lock~",
80 (int) (slash - filename), filename, slash + 1)
81 : xasprintf(".%s.~lock~", filename));
87 /* Locks the configuration file against modification by other processes and
88 * re-reads it from disk.
90 * The 'timeout' specifies the maximum number of milliseconds to wait for the
91 * config file to become free. Use 0 to avoid waiting or INT_MAX to wait
94 * Returns 0 on success, otherwise a positive errno value. On success,
95 * '*lockfilep' is set to point to a new "struct lockfile *" that may be
96 * unlocked with lockfile_unlock(). On failure, '*lockfilep' is set to
99 lockfile_lock(const char *file, int timeout, struct lockfile **lockfilep)
101 /* Only exclusive ("write") locks are supported. This is not a problem
102 * because the Open vSwitch code that currently uses lock files does so in
103 * stylized ways such that any number of readers may access a file while it
104 * is being written. */
105 long long int warn_elapsed = 1000;
106 long long int start, elapsed;
110 COVERAGE_INC(lockfile_lock);
112 lock_name = lockfile_name(file);
117 error = lockfile_try_lock(lock_name, timeout > 0, lockfilep);
119 elapsed = time_msec() - start;
120 if (elapsed > warn_elapsed) {
122 VLOG_WARN("%s: waiting for lock file, %lld ms elapsed",
125 } while (error == EINTR && (timeout == INT_MAX || elapsed < timeout));
127 if (error == EINTR) {
128 COVERAGE_INC(lockfile_timeout);
129 VLOG_WARN("%s: giving up on lock file after %lld ms",
133 COVERAGE_INC(lockfile_error);
134 if (error == EACCES) {
137 VLOG_WARN("%s: failed to lock file "
138 "(after %lld ms, with %d-ms timeout): %s",
139 lock_name, elapsed, timeout, strerror(error));
146 /* Unlocks 'lockfile', which must have been created by a call to
147 * lockfile_lock(), and frees 'lockfile'. */
149 lockfile_unlock(struct lockfile *lockfile)
152 COVERAGE_INC(lockfile_unlock);
153 lockfile_unhash(lockfile);
154 free(lockfile->name);
159 /* Marks all the currently locked lockfiles as no longer locked. It makes
160 * sense to call this function after fork(), because a child created by fork()
161 * does not hold its parents' locks. */
163 lockfile_postfork(void)
165 struct lockfile *lockfile;
167 HMAP_FOR_EACH (lockfile, hmap_node, &lock_table) {
168 if (lockfile->fd >= 0) {
169 VLOG_WARN("%s: child does not inherit lock", lockfile->name);
170 lockfile_unhash(lockfile);
176 lockfile_hash(dev_t device, ino_t inode)
178 return hash_bytes(&device, sizeof device,
179 hash_bytes(&inode, sizeof inode, 0));
182 static struct lockfile *
183 lockfile_find(dev_t device, ino_t inode)
185 struct lockfile *lockfile;
187 HMAP_FOR_EACH_WITH_HASH (lockfile, hmap_node,
188 lockfile_hash(device, inode), &lock_table) {
189 if (lockfile->device == device && lockfile->inode == inode) {
197 lockfile_unhash(struct lockfile *lockfile)
199 if (lockfile->fd >= 0) {
202 hmap_remove(&lock_table, &lockfile->hmap_node);
206 static struct lockfile *
207 lockfile_register(const char *name, dev_t device, ino_t inode, int fd)
209 struct lockfile *lockfile;
211 lockfile = lockfile_find(device, inode);
213 VLOG_ERR("%s: lock file disappeared and reappeared!", name);
214 lockfile_unhash(lockfile);
217 lockfile = xmalloc(sizeof *lockfile);
218 lockfile->name = xstrdup(name);
219 lockfile->device = device;
220 lockfile->inode = inode;
222 hmap_insert(&lock_table, &lockfile->hmap_node,
223 lockfile_hash(device, inode));
228 lockfile_try_lock(const char *name, bool block, struct lockfile **lockfilep)
237 /* Check whether we've already got a lock on that file. */
238 if (!stat(name, &s)) {
239 if (lockfile_find(s.st_dev, s.st_ino)) {
242 } else if (errno != ENOENT) {
243 VLOG_WARN("%s: failed to stat lock file: %s",
244 name, strerror(errno));
248 /* Open the lock file. */
249 fd = open(name, O_RDWR | O_CREAT, 0600);
251 VLOG_WARN("%s: failed to open lock file: %s",
252 name, strerror(errno));
256 /* Get the inode and device number for the lock table. */
258 VLOG_ERR("%s: failed to fstat lock file: %s", name, strerror(errno));
263 /* Try to lock the file. */
264 memset(&l, 0, sizeof l);
266 l.l_whence = SEEK_SET;
270 time_disable_restart();
271 error = fcntl(fd, block ? F_SETLKW : F_SETLK, &l) == -1 ? errno : 0;
272 time_enable_restart();
275 *lockfilep = lockfile_register(name, s.st_dev, s.st_ino, fd);