NAME
lockf − apply, test or remove a POSIX lock on an open file
SYNOPSIS
#include <sys/file.h>
int lockf(int fd, int cmd, off_t len);
DESCRIPTION
Apply, test or remove a POSIX lock on an open file. The file is specified by fd. This call is just an interface for fcntl(2). Valid operations are given below:
|
F_LOCK |
Set an exclusive lock to the file. Only one process may hold an exclusive lock for a given file at a given time. If the file is already locked it blocks until the previous lock is released. | ||
|
F_TLOCK |
Same as F_LOCK but never blocks and return error instead if the file is already locked. | ||
|
F_ULOCK |
Unlock the file. | ||
|
F_TEST |
Test the lock: return 0 if fd is unlocked or locked by this process; return -1, set errno to EACCES, if another process holds the lock. |
RETURN VALUE
On success, zero is returned. On error, −1 is returned, and errno is set appropriately.
ERRORS
|
EAGAIN |
The file is locked and the LOCK_NB flag was selected, or operation is prohibited because the file has been memory-mapped by another process. | ||
|
EBADF |
fd is not an open file descriptor. |
EDEADLK
Specified lock operation would cause a deadlock.
|
EINVAL |
An invalid operation was specified in fd. |
|||
|
ENOLCK |
Too many segment locks open, lock table is full. |
CONFORMING TO
SYSV
SEE ALSO
fcntl(2), flock(2). There are also locks.txt and mandatory.txt in /usr/src/linux/Documentation.