uucplock(3)

NAME

uu_lock, uu_unlock, uu_lockerr - acquire and release control

of a serial
device

LIBRARY

System Utilities Library (libutil, -lutil)

SYNOPSIS

#include <sys/types.h>
#include <libutil.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: Cannot create temporary lock file via

creat(2).

UU_LOCK_WRITE_ERR: The current process id could not be writ

ten to the
lock file via a call to write(2).

UU_LOCK_LINK_ERR: Cannot 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 pro

cess 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 re

spective 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 descrip

tion 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 processes 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 de

vices that might
be locked.

BSD March 30, 1997

BSD