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>.