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, 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 Smørgrav <des@FreeBSD.org>.

Debian                                            July 28, 2017                                     flopen(3bsd)