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, pid_t *pidp,
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 * Returns 0 on success, otherwise a positive errno value. On success,
91 * '*lockfilep' is set to point to a new "struct lockfile *" that may be
92 * unlocked with lockfile_unlock(). On failure, '*lockfilep' is set to
93 * NULL. Will not block if the lock cannot be immediately acquired. */
95 lockfile_lock(const char *file, struct lockfile **lockfilep)
97 /* Only exclusive ("write") locks are supported. This is not a problem
98 * because the Open vSwitch code that currently uses lock files does so in
99 * stylized ways such that any number of readers may access a file while it
100 * is being written. */
105 COVERAGE_INC(lockfile_lock);
107 lock_name = lockfile_name(file);
109 error = lockfile_try_lock(lock_name, &pid, lockfilep);
112 COVERAGE_INC(lockfile_error);
113 if (error == EACCES) {
117 VLOG_WARN("%s: cannot lock file because it is already locked by "
118 "pid %ld", lock_name, (long int) pid);
120 VLOG_WARN("%s: failed to lock file: %s",
121 lock_name, strerror(error));
129 /* Unlocks 'lockfile', which must have been created by a call to
130 * lockfile_lock(), and frees 'lockfile'. */
132 lockfile_unlock(struct lockfile *lockfile)
135 COVERAGE_INC(lockfile_unlock);
136 lockfile_unhash(lockfile);
137 free(lockfile->name);
142 /* Marks all the currently locked lockfiles as no longer locked. It makes
143 * sense to call this function after fork(), because a child created by fork()
144 * does not hold its parents' locks. */
146 lockfile_postfork(void)
148 struct lockfile *lockfile;
150 HMAP_FOR_EACH (lockfile, hmap_node, &lock_table) {
151 if (lockfile->fd >= 0) {
152 VLOG_WARN("%s: child does not inherit lock", lockfile->name);
153 lockfile_unhash(lockfile);
159 lockfile_hash(dev_t device, ino_t inode)
161 return hash_bytes(&device, sizeof device,
162 hash_bytes(&inode, sizeof inode, 0));
165 static struct lockfile *
166 lockfile_find(dev_t device, ino_t inode)
168 struct lockfile *lockfile;
170 HMAP_FOR_EACH_WITH_HASH (lockfile, hmap_node,
171 lockfile_hash(device, inode), &lock_table) {
172 if (lockfile->device == device && lockfile->inode == inode) {
180 lockfile_unhash(struct lockfile *lockfile)
182 if (lockfile->fd >= 0) {
185 hmap_remove(&lock_table, &lockfile->hmap_node);
189 static struct lockfile *
190 lockfile_register(const char *name, dev_t device, ino_t inode, int fd)
192 struct lockfile *lockfile;
194 lockfile = lockfile_find(device, inode);
196 VLOG_ERR("%s: lock file disappeared and reappeared!", name);
197 lockfile_unhash(lockfile);
200 lockfile = xmalloc(sizeof *lockfile);
201 lockfile->name = xstrdup(name);
202 lockfile->device = device;
203 lockfile->inode = inode;
205 hmap_insert(&lock_table, &lockfile->hmap_node,
206 lockfile_hash(device, inode));
211 lockfile_try_lock(const char *name, pid_t *pidp, struct lockfile **lockfilep)
221 /* Check whether we've already got a lock on that file. */
222 if (!stat(name, &s)) {
223 if (lockfile_find(s.st_dev, s.st_ino)) {
226 } else if (errno != ENOENT) {
227 VLOG_WARN("%s: failed to stat lock file: %s",
228 name, strerror(errno));
232 /* Open the lock file. */
233 fd = open(name, O_RDWR | O_CREAT, 0600);
235 VLOG_WARN("%s: failed to open lock file: %s",
236 name, strerror(errno));
240 /* Get the inode and device number for the lock table. */
242 VLOG_ERR("%s: failed to fstat lock file: %s", name, strerror(errno));
247 /* Try to lock the file. */
248 memset(&l, 0, sizeof l);
250 l.l_whence = SEEK_SET;
254 time_disable_restart();
255 error = fcntl(fd, F_SETLK, &l) == -1 ? errno : 0;
256 time_enable_restart();
259 *lockfilep = lockfile_register(name, s.st_dev, s.st_ino, fd);
261 if (!fcntl(fd, F_GETLK, &l) && l.l_type != F_UNLCK) {