UUCPLOCK(3)		  OpenBSD Programmer's Manual		   UUCPLOCK(3)

NAME
     uu_lock, uu_unlock, uu_lockerr, uu_lock_txfr - acquire and release
     control of a serial device

SYNOPSIS
     #include <sys/types.h>
     #include <util.h>

     int
     uu_lock(const char *ttyname);

     int
     uu_lock_txfr(const char *ttyname, pid_t pid);

     int
     uu_unlock(const char *ttyname);

     const char *
     uu_lockerr(int uu_lockresult);

DESCRIPTION
     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
     locking program.

     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_unlock().

     uu_lockerr() returns an error string representing the error
     uu_lockresult, as returned from uu_lock().

RETURN VALUES
     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(3).

     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
     specified device.

     UU_LOCK_WRITE_ERR: The new process ID could not be written to the lock
     file via a call to write(2).

ERRORS
     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.

SEE ALSO
     lseek(2), open(2), read(2), write(2)

BUGS
     It is possible that a stale lock is not recognised as such if a new
     process is assigned the same process ID as the program that left the
     stale lock.

     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
     be locked.

OpenBSD 4.9			 May 31, 2007			   OpenBSD 4.9

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