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FLOPEN(3)		    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 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
       Smorgrav	<des@FreeBSD.org>.

FreeBSD	14.3			 July 28, 2017			     FLOPEN(3)

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<https://man.freebsd.org/cgi/man.cgi?query=flopen&sektion=3&manpath=FreeBSD+14.3-RELEASE+and+Ports>

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