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+.\" Copyright (c) 1980, 1991, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)open.2	8.2 (Berkeley) 11/16/93
+.\" $FreeBSD$
+.\"
+.Dd April 13, 2011
+.Dt POSIX_FALLOCATE 2
+.Os
+.Sh NAME
+.Nm posix_fallocate
+.Nd pre-allocate storage for a range in a file
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In fcntl.h
+.Ft int
+.Fn posix_fallocate "int fd" "off_t offset" "off_t len"
+.Sh DESCRIPTION
+Required storage for the range
+.Fa offset
+to
+.Fa offset +
+.Fa len
+in the file referenced by
+.Fa fd
+is guarateed to be allocated upon successful return.
+That is, if
+.Fn posix_fallocate
+returns successfully, subsequent writes to the specified file data
+will not fail due to lack of free space on the file system storage
+media.
+Any existing file data in the specified range is unmodified.
+If
+.Fa offset +
+.Fa len
+is beyond the current file size, then
+.Fn posix_fallocate
+will adjust the file size to
+.Fa offset +
+.Fa len .
+Otherwise, the file size will not be changed.
+.Pp
+Space allocated by
+.Fn posix_fallocate
+will be freed by a successful call to
+.Xr creat 2
+or
+.Xr open 2
+that truncates the size of the file.
+Space allocated via
+.Fn posix_fallocate
+may be freed by a successful call to
+.Xr ftruncate 2
+that reduces the file size to a size smaller than
+.Fa offset +
+.Fa len .
+.Pp
+.Sh RETURN VALUES
+If successful,
+.Fn posix_fallocate
+returns zero.
+It returns -1 on failure, and sets
+.Va errno
+to indicate the error.
+.Sh ERRORS
+Possible failure conditions:
+.Bl -tag -width Er
+.It Bq Er EBADF
+The
+.Fa fd
+argument is not a valid file descriptor.
+.It Bq Er EBADF
+The
+.Fa fd
+argument references a file that was opened without write permission.
+.It Bq Er EFBIG
+The value of
+.Fa offset +
+.Fa len
+is greater than the maximum file size.
+.It Bq Er EINTR
+A signal was caught during execution.
+.It Bq Er EINVAL
+The
+.Fa len
+argument was zero or the
+.Fa offset
+argument was less than zero.
+.It Bq Er EIO
+An I/O error occurred while reading from or writing to a file system.
+.It Bq Er ENODEV
+The
+.Fa fd
+argument does not refer to a regular file.
+.It Bq Er ENOSPC
+There is insufficient free space remaining on the file system storage
+media.
+.It Bq Er ESPIPE
+The
+.Fa fd
+argument is associated with a pipe or FIFO.
+.El
+.Sh SEE ALSO
+.Xr creat 2 ,
+.Xr ftruncate 2 ,
+.Xr open 2 ,
+.Xr unlink 2
+.Sh STANDARDS
+The
+.Fn posix_fallocate
+system call conforms to
+.St -p1003.1-2004 .
+.Sh HISTORY
+The
+.Fn posix_fallocate
+function appeared in
+.Fx 9.0 .
+.Sh AUTHORS
+.Fn posix_fallocate
+and this manual page were initially written by
+.An Matthew Fleming Aq mdf@FreeBSD.org .