LOCKF(3)                COMMAND REFERENCE                LOCKF(3)



NAME
     lockf - advisory record locking on files

SYNOPSIS
     #include <unistd.h>

     #define   F_ULOCK   0    /* Unlock a previously locked section */
     #define   F_LOCK    1    /* Lock a section for exclusive use */
     #define   F_TLOCK   2    /* Test and lock a section (non-blocking) */
     #define   F_TEST    3    /* Test section for other process' locks */
     lockf(fd, cmd, size)
     int fd, cmd;
     long size;

DESCRIPTION
     Routine lockf may be used to test, apply or remove an
     advisory record lock on the file associated with the open
     descriptor fd.  (See fcntl(2) for more information about
     advisory record locking.)

     A lock is obtained by specifying a cmd parameter of F_LOCK
     or F_TLOCK.  To unlock an existing lock, the F_ULOCK cmd is
     used.  F_TEST is used to detect if a lock by another process
     is present on the specified segment.

     F_LOCK and F_TLOCK requests differ only by the action taken
     if the lock may not be immediately granted.  F_TLOCK causes
     the function to return a -1 and set errno to EAGAIN if the
     section is already locked by another process.  F_LOCK causes
     the process to sleep until the lock may be granted or a
     signal is caught.

     Size is the number of contiguous bytes to be locked or
     unlocked.  The lock starts at the current file offset in the
     file and extends forward for a positive size or backward for
     a negative size (preceding but not including the current
     offset).  A segment need not be allocated to the file in
     order to be locked;  however, a segment may not extend to a
     negative offset relative to the beginning of the file.  If
     size is zero, the lock extends from the current offset
     through the end-of-file; if such a lock starts at offset 0,
     then the entire file is locked (regardless of future file
     extensions).

NOTES
     The descriptor fd must have been opened with O_WRONLY or
     O_RDWR permission in order to establish locks with this
     function call.

     All locks associated with a file for a given process are
     removed when the file is closed or the process terminates.
     Locks are not inherited by the child process in a fork(2)



Printed 3/13/89                                                 1

LOCKF(3)                COMMAND REFERENCE                LOCKF(3)



     system call.

RETURN VALUE
     Zero is returned on success, -1 on error, with an error code
     stored in errno.

     The lockf fails if one or more of the following are true:

     EBADF          fd is not a valid open descriptor

     EBADF          cmd is F_LOCK or F_TLOCK and the process does
                    not have write permission on the file

     EAGAIN         cmd is F_TLOCK or F_TEST and the section is
                    already locked by another process

     EINTR          cmd is F_LOCK and a signal interrupted the
                    process while it was waiting for the lock to
                    be granted

     ENOLCK         cmd is F_LOCK, F_TLOCK, or F_ULOCK and there
                    are no file lock entries available

CAVEATS
     File locks obtained through the lockf mechanism do not
     interact in any way with those acquired via flock(2); they
     do, however, work correctly with the locks claimed by
     fcntl(2).

SEE ALSO
     fcntl(2), lockd(8c).
























Printed 3/13/89                                                 2

%%index%%
na:264,92;
sy:356,2975;
de:3331,2112;5779,19;
rv:5798,944;
ca:6742,351;
se:7093,152;
%%index%%000000000118