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UUCPLOCK(3)		 BSD Library Functions Manual		   UUCPLOCK(3)

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

     System Utilities Library (libutil,	-lutil)

     #include <sys/types.h>
     #include <libutil.h>

     uu_lock(const char	*ttyname);

     uu_lock_txfr(const	char *ttyname, pid_t pid);

     uu_unlock(const char *ttyname);

     const char	*
     uu_lockerr(int uu_lockresult);

     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 call-
     ing uu_unlock().

     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 re-
     turned.  uu_lockerr() uses	the current value of errno to determine	the
     exact error.  Care	should be made not to allow errno to be	changed	be-
     tween 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).

     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 pro-
     cesses is assigned	the same processes 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.

BSD				March 30, 1997				   BSD


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