1 /* Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013, 2014 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_error);
39 COVERAGE_DEFINE(lockfile_unlock);
42 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 ovs_mutex lock_table_mutex = OVS_MUTEX_INITIALIZER;
57 static struct hmap lock_table__ = HMAP_INITIALIZER(&lock_table__);
58 static struct hmap *const lock_table OVS_GUARDED_BY(lock_table_mutex)
61 static void lockfile_unhash(struct lockfile *);
62 static int lockfile_try_lock(const char *name, pid_t *pidp,
63 struct lockfile **lockfilep)
64 OVS_REQUIRES(&lock_table_mutex);
65 static void lockfile_do_unlock(struct lockfile * lockfile)
66 OVS_REQUIRES(&lock_table_mutex);
68 /* Returns the name of the lockfile that would be created for locking a file
69 * named 'filename_'. The caller is responsible for freeing the returned name,
70 * with free(), when it is no longer needed. */
72 lockfile_name(const char *filename_)
78 /* If 'filename_' is a symlink, base the name of the lockfile on the
79 * symlink's target rather than the name of the symlink. That way, if a
80 * file is symlinked, but there is no symlink for its lockfile, then there
81 * is only a single lockfile for both the source and the target of the
82 * symlink, not one for each. */
83 filename = follow_symlinks(filename_);
84 slash = strrchr(filename, '/');
86 ? xasprintf("%.*s/.%s.~lock~",
87 (int) (slash - filename), filename, slash + 1)
88 : xasprintf(".%s.~lock~", filename));
94 /* Locks the configuration file against modification by other processes and
95 * re-reads it from disk.
97 * Returns 0 on success, otherwise a positive errno value. On success,
98 * '*lockfilep' is set to point to a new "struct lockfile *" that may be
99 * unlocked with lockfile_unlock(). On failure, '*lockfilep' is set to
100 * NULL. Will not block if the lock cannot be immediately acquired. */
102 lockfile_lock(const char *file, struct lockfile **lockfilep)
104 /* Only exclusive ("write") locks are supported. This is not a problem
105 * because the Open vSwitch code that currently uses lock files does so in
106 * stylized ways such that any number of readers may access a file while it
107 * is being written. */
112 COVERAGE_INC(lockfile_lock);
114 lock_name = lockfile_name(file);
116 ovs_mutex_lock(&lock_table_mutex);
117 error = lockfile_try_lock(lock_name, &pid, lockfilep);
118 ovs_mutex_unlock(&lock_table_mutex);
121 COVERAGE_INC(lockfile_error);
122 if (error == EACCES) {
125 if (pid == getpid()) {
126 VLOG_WARN("%s: cannot lock file because this process has already "
127 "locked it", lock_name);
129 VLOG_WARN("%s: cannot lock file because it is already locked by "
130 "pid %ld", lock_name, (long int) pid);
132 VLOG_WARN("%s: failed to lock file: %s",
133 lock_name, ovs_strerror(error));
141 /* Unlocks 'lockfile', which must have been created by a call to
142 * lockfile_lock(), and frees 'lockfile'. */
144 lockfile_unlock(struct lockfile *lockfile)
147 ovs_mutex_lock(&lock_table_mutex);
148 lockfile_do_unlock(lockfile);
149 ovs_mutex_unlock(&lock_table_mutex);
151 COVERAGE_INC(lockfile_unlock);
152 free(lockfile->name);
157 /* Marks all the currently locked lockfiles as no longer locked. It makes
158 * sense to call this function after fork(), because a child created by fork()
159 * does not hold its parents' locks. */
161 lockfile_postfork(void)
163 struct lockfile *lockfile;
165 ovs_mutex_lock(&lock_table_mutex);
166 HMAP_FOR_EACH (lockfile, hmap_node, lock_table) {
167 if (lockfile->fd >= 0) {
168 VLOG_WARN("%s: child does not inherit lock", lockfile->name);
169 lockfile_unhash(lockfile);
172 ovs_mutex_unlock(&lock_table_mutex);
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) OVS_REQUIRES(&lock_table_mutex)
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) OVS_REQUIRES(&lock_table_mutex)
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)
208 OVS_REQUIRES(&lock_table_mutex)
210 struct lockfile *lockfile;
212 lockfile = lockfile_find(device, inode);
214 VLOG_ERR("%s: lock file disappeared and reappeared!", name);
215 lockfile_unhash(lockfile);
218 lockfile = xmalloc(sizeof *lockfile);
219 lockfile->name = xstrdup(name);
220 lockfile->device = device;
221 lockfile->inode = inode;
223 hmap_insert(lock_table, &lockfile->hmap_node,
224 lockfile_hash(device, inode));
230 lockfile_do_unlock(struct lockfile *lockfile)
231 OVS_REQUIRES(&lock_table_mutex)
233 if (lockfile->fd >= 0) {
237 overl.OffsetHigh = 0;
238 UnlockFileEx(lockfile->lock_handle, 0, 1, 0, &overl);
246 lockfile_try_lock(const char *name, pid_t *pidp, struct lockfile **lockfilep)
247 OVS_REQUIRES(&lock_table_mutex)
252 struct lockfile *lockfile;
257 fd = open(name, O_RDWR | O_CREAT, 0600);
259 VLOG_WARN("%s: failed to open lock file: %s",
260 name, ovs_strerror(errno));
264 lock_handle = (HANDLE)_get_osfhandle(fd);
265 if (lock_handle < 0) {
266 VLOG_WARN("%s: failed to get the file handle: %s",
267 name, ovs_strerror(errno));
271 /* Lock the file 'name' for the region that includes just the first
275 overl.OffsetHigh = 0;
276 retval = LockFileEx(lock_handle, LOCKFILE_EXCLUSIVE_LOCK
277 | LOCKFILE_FAIL_IMMEDIATELY, 0, 1, 0, &overl);
279 VLOG_WARN("Failed to lock file : %s", ovs_lasterror_to_string());
283 lockfile = xmalloc(sizeof *lockfile);
284 lockfile->name = xstrdup(name);
286 lockfile->lock_handle = lock_handle;
288 *lockfilep = lockfile;
293 lockfile_do_unlock(struct lockfile *lockfile)
295 lockfile_unhash(lockfile);
299 lockfile_try_lock(const char *name, pid_t *pidp, struct lockfile **lockfilep)
300 OVS_REQUIRES(&lock_table_mutex)
310 /* Check whether we've already got a lock on that file. */
311 if (!stat(name, &s)) {
312 if (lockfile_find(s.st_dev, s.st_ino)) {
316 } else if (errno != ENOENT) {
317 VLOG_WARN("%s: failed to stat lock file: %s",
318 name, ovs_strerror(errno));
322 /* Open the lock file. */
323 fd = open(name, O_RDWR | O_CREAT, 0600);
325 VLOG_WARN("%s: failed to open lock file: %s",
326 name, ovs_strerror(errno));
330 /* Get the inode and device number for the lock table. */
332 VLOG_ERR("%s: failed to fstat lock file: %s",
333 name, ovs_strerror(errno));
338 /* Try to lock the file. */
339 memset(&l, 0, sizeof l);
341 l.l_whence = SEEK_SET;
345 error = fcntl(fd, F_SETLK, &l) == -1 ? errno : 0;
348 *lockfilep = lockfile_register(name, s.st_dev, s.st_ino, fd);
350 if (!fcntl(fd, F_GETLK, &l) && l.l_type != F_UNLCK) {