freebsd-nq/lib/libutil/flopen.3

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.Dd July 28, 2017
.Dt FLOPEN 3
.Os
.Sh NAME
.Nm flopen ,
.Nm flopenat
.Nd "Reliably open and lock a file"
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In sys/fcntl.h
.In libutil.h
.Ft int
.Fn flopen "const char *path" "int flags"
.Ft int
.Fn flopen "const char *path" "int flags" "mode_t mode"
.Ft int
.Fn flopenat "int fd" "const char *path" "int flags"
.Ft int
.Fn flopenat "int fd" "const char *path" "int flags" "mode_t mode"
.Sh DESCRIPTION
The
.Fn flopen
function opens or creates a file and acquires an exclusive lock on it.
It is essentially equivalent with calling
.Fn open
with the same parameters followed by
.Fn flock
with an
.Fa operation
argument of
.Dv LOCK_EX ,
except that
.Fn 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.
.Pp
If
.Fa flags
includes
.Dv O_NONBLOCK
and the file is already locked,
.Fn flopen
will fail and set
.Va errno
to
.Dv EWOULDBLOCK .
.Pp
As with
.Fn open ,
the additional
.Fa mode
argument is required if
.Fa flags
includes
.Dv O_CREAT .
.Pp
The
.Fn flopenat
function is equivalent to the
.Fn flopen
function except in the case where the
.Fa path
specifies a relative path.
In this case the file to be opened is determined relative to the directory
associated with the file descriptor
.Fa fd
instead of the current working directory.
If
.Fn flopenat
is passed the special value
.Dv AT_FDCWD
in the
.Fa fd
parameter, the current working directory is used
and the behavior is identical to a call to
.Fn flopen .
.Sh RETURN VALUES
If successful,
.Fn flopen
returns a valid file descriptor.
Otherwise, it returns -1, and sets
.Va errno
as described in
.Xr flock 2
and
.Xr open 2 .
.Sh SEE ALSO
.Xr errno 2 ,
.Xr flock 2 ,
.Xr open 2
.Sh AUTHORS
.An -nosplit
The
.Nm
function and this manual page were written by
.An Dag-Erling Sm\(/orgrav Aq Mt des@FreeBSD.org .