uu_lock, uu_unlock, uu_lockerr -- acquire and release control of a serial
System Utilities Library (libutil, -lutil)
uu_lock(const char *ttyname);
uu_lock_txfr(const char *ttyname, pid_t pid);
uu_unlock(const char *ttyname);
const char *
The uu_lock() function attempts to create a lock file called
/var/spool/lock/LCK.. with a suffix given by the passed ttyname. If the
file already exists, it is expected to contain the process id of the
If the file does not already exist, or the owning process given by the
process id found in the lock file is no longer running, uu_lock() will
write its own process id into the file and return success.
uu_lock_txfr() transfers lock ownership to another process. uu_lock()
must have previously been successful.
uu_unlock() removes the lockfile created by uu_lock() for the given
ttyname. Care should be taken that uu_lock() was successful before calling
uu_lockerr() returns an error string representing the error
uu_lockresult, as returned from uu_lock().
uu_unlock() returns 0 on success and -1 on failure.
uu_lock() may return any of the following values:
UU_LOCK_INUSE: The lock is in use by another process.
UU_LOCK_OK: The lock was successfully created.
UU_LOCK_OPEN_ERR: The lock file could not be opened via open(2).
UU_LOCK_READ_ERR: The lock file could not be read via read(2).
UU_LOCK_CREAT_ERR: Can't create temporary lock file via creat(2).
UU_LOCK_WRITE_ERR: The current process id could not be written to the
lock file via a call to write(2).
UU_LOCK_LINK_ERR: Can't link temporary lock file via link(2).
UU_LOCK_TRY_ERR: Locking attempts are failed after 5 tries.
If a value of UU_LOCK_OK is passed to uu_lockerr(), an empty string is
returned. Otherwise, a string specifying the reason for failure is
returned. uu_lockerr() uses the current value of errno to determine the
exact error. Care should be made not to allow errno to be changed
between calls to uu_lock() and uu_lockerr().
uu_lock_txfr() may return any of the following values:
UU_LOCK_OK: The transfer was successful. The specified process now holds
the device lock.
UU_LOCK_OWNER_ERR: The current process does not already own a lock on the
UU_LOCK_WRITE_ERR: The new process id could not be written to the lock
file via a call to write(2).
If uu_lock() returns one of the error values above, the global value
errno can be used to determine the cause. Refer to the respective manual
pages for further details.
uu_unlock() will set the global variable errno to reflect the reason that
the lock file could not be removed. Refer to the description of
unlink(2) for further details.
lseek(2), open(2), read(2), write(2)
It is possible that a stale lock is not recognised as such if a new processes
is assigned the same processes id as the program that left the
The calling process must have write permissions to the /var/spool/lock
directory. There is no mechanism in place to ensure that the permissions
of this directory are the same as those of the serial devices that might
FreeBSD 5.2.1 March 30, 1997 FreeBSD 5.2.1 [ Back ]