changing lock mechanism
Systems can suffer power interruptions whilst .lock files are in /etc, preventing scripts and other automation tools from updating shadow's files which persist across boots. This commit replaces that mechanism with file locking to avoid problems of power interruption/crashing. Minor tweak to groupmems man page, requested by 'xx' on IRC. Signed-off-by: ed neville <ed@s5h.net>
This commit is contained in:
parent
bc18c184e5
commit
65470e5c7d
184
lib/commonio.c
184
lib/commonio.c
@ -32,8 +32,6 @@
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/* local function prototypes */
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static int lrename (const char *, const char *);
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static int check_link_count (const char *file, bool log);
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static int do_lock_file (const char *file, const char *lock, bool log);
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static /*@null@*/ /*@dependent@*/FILE *fopen_set_perms (
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const char *name,
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const char *mode,
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@ -91,150 +89,6 @@ int lrename (const char *old, const char *new)
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return res;
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}
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static int check_link_count (const char *file, bool log)
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{
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struct stat sb;
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if (stat (file, &sb) != 0) {
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if (log) {
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(void) fprintf (shadow_logfd,
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"%s: %s file stat error: %s\n",
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shadow_progname, file, strerror (errno));
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}
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return 0;
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}
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if (sb.st_nlink != 2) {
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if (log) {
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(void) fprintf (shadow_logfd,
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"%s: %s: lock file already used (nlink: %u)\n",
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shadow_progname, file, sb.st_nlink);
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}
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return 0;
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}
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return 1;
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}
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static int do_lock_file (const char *file, const char *lock, bool log)
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{
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int fd;
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pid_t pid;
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ssize_t len;
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int retval;
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char buf[32];
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fd = open (file, O_CREAT | O_TRUNC | O_WRONLY, 0600);
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if (-1 == fd) {
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if (log) {
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(void) fprintf (shadow_logfd,
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"%s: %s: %s\n",
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shadow_progname, file, strerror (errno));
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}
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return 0;
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}
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pid = getpid ();
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snprintf (buf, sizeof buf, "%lu", (unsigned long) pid);
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len = (ssize_t) strlen (buf) + 1;
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if (write (fd, buf, (size_t) len) != len) {
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if (log) {
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(void) fprintf (shadow_logfd,
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"%s: %s file write error: %s\n",
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shadow_progname, file, strerror (errno));
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}
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(void) close (fd);
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unlink (file);
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return 0;
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}
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if (fdatasync (fd) == -1) {
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if (log) {
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(void) fprintf (shadow_logfd,
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"%s: %s file sync error: %s\n",
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shadow_progname, file, strerror (errno));
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}
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(void) close (fd);
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unlink (file);
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return 0;
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}
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close (fd);
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if (link (file, lock) == 0) {
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retval = check_link_count (file, log);
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unlink (file);
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return retval;
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}
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fd = open (lock, O_RDWR);
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if (-1 == fd) {
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if (log) {
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(void) fprintf (shadow_logfd,
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"%s: %s: %s\n",
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shadow_progname, lock, strerror (errno));
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}
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unlink (file);
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errno = EINVAL;
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return 0;
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}
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len = read (fd, buf, sizeof (buf) - 1);
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close (fd);
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if (len <= 0) {
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if (log) {
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(void) fprintf (shadow_logfd,
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"%s: existing lock file %s without a PID\n",
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shadow_progname, lock);
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}
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unlink (file);
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errno = EINVAL;
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return 0;
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}
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buf[len] = '\0';
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if (get_pid (buf, &pid) == 0) {
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if (log) {
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(void) fprintf (shadow_logfd,
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"%s: existing lock file %s with an invalid PID '%s'\n",
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shadow_progname, lock, buf);
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}
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unlink (file);
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errno = EINVAL;
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return 0;
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}
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if (kill (pid, 0) == 0) {
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if (log) {
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(void) fprintf (shadow_logfd,
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"%s: lock %s already used by PID %lu\n",
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shadow_progname, lock, (unsigned long) pid);
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}
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unlink (file);
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errno = EEXIST;
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return 0;
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}
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if (unlink (lock) != 0) {
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if (log) {
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(void) fprintf (shadow_logfd,
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"%s: cannot get lock %s: %s\n",
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shadow_progname, lock, strerror (errno));
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}
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unlink (file);
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return 0;
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}
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retval = 0;
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if (link (file, lock) == 0) {
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retval = check_link_count (file, log);
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} else {
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if (log) {
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(void) fprintf (shadow_logfd,
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"%s: cannot get lock %s: %s\n",
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shadow_progname, lock, strerror (errno));
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}
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}
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unlink (file);
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return retval;
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}
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static /*@null@*/ /*@dependent@*/FILE *fopen_set_perms (
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const char *name,
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@ -349,6 +203,30 @@ bool commonio_present (const struct commonio_db *db)
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}
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int do_fcntl_lock (const char *file, bool log, short type)
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{
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int fd;
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struct flock lck = {
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.l_type = type,
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.l_whence = SEEK_SET,
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.l_start = 0,
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.l_len = 0,
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};
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fd = open (file, O_WRONLY, 0600);
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if (-1 == fd) {
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if (log) {
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(void) fprintf (shadow_logfd, "%s: %s: %s\n",
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shadow_progname, file, strerror (errno));
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}
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return 0;
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}
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fcntl (fd, F_OFD_SETLKW, &lck);
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close(fd);
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return(1);
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}
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int commonio_lock_nowait (struct commonio_db *db, bool log)
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{
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char* file = NULL;
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@ -372,8 +250,8 @@ int commonio_lock_nowait (struct commonio_db *db, bool log)
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}
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snprintf (file, file_len, "%s.%lu",
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db->filename, (unsigned long) getpid ());
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snprintf (lock, lock_file_len, "%s.lock", db->filename);
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if (do_lock_file (file, lock, log) != 0) {
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if (do_fcntl_lock (db->filename, log, F_WRLCK | F_RDLCK) != 0) {
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db->locked = true;
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lock_count++;
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err = 1;
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@ -471,8 +349,6 @@ static void dec_lock_count (void)
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int commonio_unlock (struct commonio_db *db)
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{
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char lock[1024];
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if (db->isopen) {
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db->readonly = true;
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if (commonio_close (db) == 0) {
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@ -483,13 +359,9 @@ int commonio_unlock (struct commonio_db *db)
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}
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}
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if (db->locked) {
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/*
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* Unlock in reverse order: remove the lock file,
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* then call ulckpwdf() (if used) on last unlock.
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*/
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db->locked = false;
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snprintf (lock, sizeof lock, "%s.lock", db->filename);
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unlink (lock);
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do_fcntl_lock (db->filename, false, F_UNLCK);
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dec_lock_count ();
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return 1;
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}
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@ -123,6 +123,7 @@ extern int commonio_setname (struct commonio_db *, const char *);
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extern bool commonio_present (const struct commonio_db *db);
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extern int commonio_lock (struct commonio_db *);
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extern int commonio_lock_nowait (struct commonio_db *, bool log);
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extern int do_fcntl_lock (const char *file, bool log, short type);
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extern int commonio_open (struct commonio_db *, int);
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extern /*@observer@*/ /*@null@*/const void *commonio_locate (struct commonio_db *, const char *);
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extern int commonio_update (struct commonio_db *, const void *);
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@ -167,7 +167,7 @@
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<programlisting>
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$ groupadd -r groups
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$ chmod 2710 groupmems
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$ chown root.groups groupmems
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$ chown root:groups groupmems
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$ groupmems -g groups -a gk4
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</programlisting>
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</refsect1>
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