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.
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.