flopen(3bsd) LOCAL flopen(3bsd)
NAME
flopen, flopenat — Reliably open and lock a file
LIBRARY
Utility functions from BSD systems (libbsd, -lbsd)
SYNOPSIS
#include <sys/fcntl.h>
#include <libutil.h>
(See libbsd(7) for include usage.)
int
flopen(const char *path, int flags);
int
flopen(const char *path, int flags, mode_t mode);
int
flopenat(int fd, const char *path, int flags);
int
flopenat(int fd, const char *path, int flags, mode_t mode);
DESCRIPTION
The flopen() function opens or creates a file and acquires an exclusive
lock on it. It is essentially equivalent with calling open() with the
same parameters followed by flock() with an operation argument of
LOCK_EX, except that flopen() will attempt to detect and handle races
that may occur between opening / creating the file and locking it. Thus,
it is well suited for opening lock files, PID files, spool files, mail-
boxes and other kinds of files which are used for synchronization between
processes.
If flags includes O_NONBLOCK and the file is already locked, flopen()
will fail and set errno to EWOULDBLOCK.
As with open(), the additional mode argument is required if flags in-
cludes O_CREAT.
The flopenat() function is equivalent to the flopen() function except in
the case where the path specifies a relative path. In this case the file
to be opened is determined relative to the directory associated with the
file descriptor fd instead of the current working directory. If
flopenat() is passed the special value AT_FDCWD in the fd parameter, the
current working directory is used and the behavior is identical to a call
to flopen().
RETURN VALUES
If successful, flopen() returns a valid file descriptor. Otherwise, it
returns -1, and sets errno as described in flock(2) and open(2).
SEE ALSO
errno(2), flock(2), open(2)
AUTHORS
The flopen function and this manual page were written by Dag-Erling
Smørgrav <des@FreeBSD.org>.
BSD July 28, 2017 BSD
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