применить, проверить или снять блокировку POSIX для открытого файла (apply, test or remove a POSIX lock on an open file)
Имя (Name)
lockf - apply, test or remove a POSIX lock on an open file
Синопсис (Synopsis)
#include <unistd.h>
int lockf(int fd, int cmd, off_t len);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
lockf():
_XOPEN_SOURCE >= 500
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Описание (Description)
Apply, test, or remove a POSIX lock on a section of an open file.
The file is specified by fd, a file descriptor open for writing,
the action by cmd, and the section consists of byte positions
pos..pos+len-1 if len is positive, and pos-len..pos-1 if len is
negative, where pos is the current file position, and if len is
zero, the section extends from the current file position to
infinity, encompassing the present and future end-of-file
positions. In all cases, the section may extend past current
end-of-file.
On Linux, lockf() is just an interface on top of fcntl(2)
locking. Many other systems implement lockf() in this way, but
note that POSIX.1 leaves the relationship between lockf() and
fcntl(2) locks unspecified. A portable application should
probably avoid mixing calls to these interfaces.
Valid operations are given below:
F_LOCK Set an exclusive lock on the specified section of the
file. If (part of) this section is already locked, the
call blocks until the previous lock is released. If this
section overlaps an earlier locked section, both are
merged. File locks are released as soon as the process
holding the locks closes some file descriptor for the
file. A child process does not inherit these locks.
F_TLOCK
Same as F_LOCK but the call never blocks and returns an
error instead if the file is already locked.
F_ULOCK
Unlock the indicated section of the file. This may cause
a locked section to be split into two locked sections.
F_TEST Test the lock: return 0 if the specified section is
unlocked or locked by this process; return -1, set errno
to EAGAIN (EACCES on some other systems), if another
process holds a lock.
Возвращаемое значение (Return value)
On success, zero is returned. On error, -1 is returned, and
errno is set to indicate the error.
Ошибки (Error)
EACCES or EAGAIN
The file is locked and F_TLOCK or F_TEST was specified, or
the operation is prohibited because the file has been
memory-mapped by another process.
EBADF fd is not an open file descriptor; or cmd is F_LOCK or
F_TLOCK and fd is not a writable file descriptor.
EDEADLK
The command was F_LOCK and this lock operation would cause
a deadlock.
EINTR While waiting to acquire a lock, the call was interrupted
by delivery of a signal caught by a handler; see
signal(7).
EINVAL An invalid operation was specified in cmd.
ENOLCK Too many segment locks open, lock table is full.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│lockf() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008, SVr4.
Смотри также (See also)
fcntl(2), flock(2)
locks.txt and mandatory-locking.txt in the Linux kernel source
directory Documentation/filesystems (on older kernels, these
files are directly under the Documentation directory, and
mandatory-locking.txt is called mandatory.txt)
