FLOPEN(3)              FreeBSD Library Functions Manual              FLOPEN(3)

NAME
     flopen, flopenat - Reliably open and lock a file

LIBRARY
     System Utilities Library (libutil, -lutil)

SYNOPSIS
     #include <sys/fcntl.h>
     #include <libutil.h>

     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,
     mailboxes 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
     includes 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
     Sm/rgrav <des@FreeBSD.org>.

FreeBSD 13.1-RELEASE-p6          July 28, 2017         FreeBSD 13.1-RELEASE-p6