1 /* Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 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.
30 #include "ovs-thread.h"
35 VLOG_DEFINE_THIS_MODULE(lockfile);
37 COVERAGE_DEFINE(lockfile_lock);
38 COVERAGE_DEFINE(lockfile_timeout);
39 COVERAGE_DEFINE(lockfile_error);
40 COVERAGE_DEFINE(lockfile_unlock);
43 struct hmap_node hmap_node;
52 * We have to do this stupid dance because POSIX says that closing *any* file
53 * descriptor for a file on which a process holds a lock drops *all* locks on
54 * that file. That means that we can't afford to open a lockfile more than
56 static struct hmap lock_table = HMAP_INITIALIZER(&lock_table);
58 /* Protects 'lock_table'. */
59 static pthread_mutex_t lock_table_mutex = PTHREAD_MUTEX_INITIALIZER;
61 static void lockfile_unhash(struct lockfile *);
62 static int lockfile_try_lock(const char *name, pid_t *pidp,
63 struct lockfile **lockfilep);
65 /* Returns the name of the lockfile that would be created for locking a file
66 * named 'filename_'. The caller is responsible for freeing the returned name,
67 * with free(), when it is no longer needed. */
69 lockfile_name(const char *filename_)
75 /* If 'filename_' is a symlink, base the name of the lockfile on the
76 * symlink's target rather than the name of the symlink. That way, if a
77 * file is symlinked, but there is no symlink for its lockfile, then there
78 * is only a single lockfile for both the source and the target of the
79 * symlink, not one for each. */
80 filename = follow_symlinks(filename_);
81 slash = strrchr(filename, '/');
83 ? xasprintf("%.*s/.%s.~lock~",
84 (int) (slash - filename), filename, slash + 1)
85 : xasprintf(".%s.~lock~", filename));
91 /* Locks the configuration file against modification by other processes and
92 * re-reads it from disk.
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
97 * NULL. Will not block if the lock cannot be immediately acquired. */
99 lockfile_lock(const char *file, 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. */
109 COVERAGE_INC(lockfile_lock);
111 lock_name = lockfile_name(file);
113 xpthread_mutex_lock(&lock_table_mutex);
114 error = lockfile_try_lock(lock_name, &pid, lockfilep);
115 xpthread_mutex_unlock(&lock_table_mutex);
118 COVERAGE_INC(lockfile_error);
119 if (error == EACCES) {
123 VLOG_WARN("%s: cannot lock file because it is already locked by "
124 "pid %ld", lock_name, (long int) pid);
126 VLOG_WARN("%s: failed to lock file: %s",
127 lock_name, ovs_strerror(error));
135 /* Unlocks 'lockfile', which must have been created by a call to
136 * lockfile_lock(), and frees 'lockfile'. */
138 lockfile_unlock(struct lockfile *lockfile)
141 xpthread_mutex_lock(&lock_table_mutex);
142 lockfile_unhash(lockfile);
143 xpthread_mutex_unlock(&lock_table_mutex);
145 COVERAGE_INC(lockfile_unlock);
146 free(lockfile->name);
151 /* Marks all the currently locked lockfiles as no longer locked. It makes
152 * sense to call this function after fork(), because a child created by fork()
153 * does not hold its parents' locks. */
155 lockfile_postfork(void)
157 struct lockfile *lockfile;
159 HMAP_FOR_EACH (lockfile, hmap_node, &lock_table) {
160 if (lockfile->fd >= 0) {
161 VLOG_WARN("%s: child does not inherit lock", lockfile->name);
162 lockfile_unhash(lockfile);
168 lockfile_hash(dev_t device, ino_t inode)
170 return hash_bytes(&device, sizeof device,
171 hash_bytes(&inode, sizeof inode, 0));
174 static struct lockfile *
175 lockfile_find(dev_t device, ino_t inode)
177 struct lockfile *lockfile;
179 HMAP_FOR_EACH_WITH_HASH (lockfile, hmap_node,
180 lockfile_hash(device, inode), &lock_table) {
181 if (lockfile->device == device && lockfile->inode == inode) {
189 lockfile_unhash(struct lockfile *lockfile)
191 if (lockfile->fd >= 0) {
194 hmap_remove(&lock_table, &lockfile->hmap_node);
198 static struct lockfile *
199 lockfile_register(const char *name, dev_t device, ino_t inode, int fd)
201 struct lockfile *lockfile;
203 lockfile = lockfile_find(device, inode);
205 VLOG_ERR("%s: lock file disappeared and reappeared!", name);
206 lockfile_unhash(lockfile);
209 lockfile = xmalloc(sizeof *lockfile);
210 lockfile->name = xstrdup(name);
211 lockfile->device = device;
212 lockfile->inode = inode;
214 hmap_insert(&lock_table, &lockfile->hmap_node,
215 lockfile_hash(device, inode));
220 lockfile_try_lock(const char *name, pid_t *pidp, struct lockfile **lockfilep)
230 /* Check whether we've already got a lock on that file. */
231 if (!stat(name, &s)) {
232 if (lockfile_find(s.st_dev, s.st_ino)) {
235 } else if (errno != ENOENT) {
236 VLOG_WARN("%s: failed to stat lock file: %s",
237 name, ovs_strerror(errno));
241 /* Open the lock file. */
242 fd = open(name, O_RDWR | O_CREAT, 0600);
244 VLOG_WARN("%s: failed to open lock file: %s",
245 name, ovs_strerror(errno));
249 /* Get the inode and device number for the lock table. */
251 VLOG_ERR("%s: failed to fstat lock file: %s",
252 name, ovs_strerror(errno));
257 /* Try to lock the file. */
258 memset(&l, 0, sizeof l);
260 l.l_whence = SEEK_SET;
264 error = fcntl(fd, F_SETLK, &l) == -1 ? errno : 0;
267 *lockfilep = lockfile_register(name, s.st_dev, s.st_ino, fd);
269 if (!fcntl(fd, F_GETLK, &l) && l.l_type != F_UNLCK) {