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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.
+.\"
+.\"     @(#)lseek.2	8.3 (Berkeley) 4/19/94
+.\" $FreeBSD$
+.\"
+.Dd April 5, 2007
+.Dt LSEEK 2
+.Os
+.Sh NAME
+.Nm lseek
+.Nd reposition read/write file offset
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In unistd.h
+.Ft off_t
+.Fn lseek "int fildes" "off_t offset" "int whence"
+.Sh DESCRIPTION
+The
+.Fn lseek
+system call repositions the offset of the file descriptor
+.Fa fildes
+to the
+argument
+.Fa offset
+according to the directive
+.Fa whence .
+The argument
+.Fa fildes
+must be an open
+file descriptor.
+The
+.Fn lseek
+system call
+repositions the file position pointer associated with the file
+descriptor
+.Fa fildes
+as follows:
+.Bl -item -offset indent
+.It
+If
+.Fa whence
+is
+.Dv SEEK_SET ,
+the offset is set to
+.Fa offset
+bytes.
+.It
+If
+.Fa whence
+is
+.Dv SEEK_CUR ,
+the offset is set to its current location plus
+.Fa offset
+bytes.
+.It
+If
+.Fa whence
+is
+.Dv SEEK_END ,
+the offset is set to the size of the
+file plus
+.Fa offset
+bytes.
+.It
+If
+.Fa whence
+is
+.Dv SEEK_HOLE ,
+the offset of the start of the next hole greater than or equal to the supplied
+.Fa offset
+is returned.
+The definition of a hole is provided below.
+.It
+If
+.Fa whence
+is
+.Dv SEEK_DATA ,
+the offset is set to the start of the next non-hole file region greater
+than or equal to the supplied
+.Fa offset .
+.El
+.Pp
+The
+.Fn lseek
+system call allows the file offset to be set beyond the end
+of the existing end-of-file of the file.
+If data is later written
+at this point, subsequent reads of the data in the gap return
+bytes of zeros (until data is actually written into the gap).
+.Pp
+Some devices are incapable of seeking.
+The value of the pointer
+associated with such a device is undefined.
+.Pp
+A
+.Qq hole
+is defined as a contiguous range of bytes in a file, all having the value of
+zero, but not all zeros in a file are guaranteed to be represented as holes
+returned with
+.Dv SEEK_HOLE .
+File systems are allowed to expose ranges of zeros with
+.Dv SEEK_HOLE ,
+but not required to.
+Applications can use
+.Dv SEEK_HOLE
+to optimise their behavior for ranges of zeros, but must not depend on it to
+find all such ranges in a file.
+The existence of a hole at the end of every data region allows for easy
+programming and implies that a virtual hole exists at the end of the file.
+Applications should use
+.Fn fpathconf _PC_MIN_HOLE_SIZE
+or
+.Fn pathconf _PC_MIN_HOLE_SIZE
+to determine if a file system supports
+.Dv SEEK_HOLE .
+See
+.Xr pathconf 2 .
+.Pp
+For file systems that do not supply information about holes, the file will be
+represented as one entire data region.
+.Sh RETURN VALUES
+Upon successful completion,
+.Fn lseek
+returns the resulting offset location as measured in bytes from the
+beginning of the file.
+Otherwise,
+a value of -1 is returned and
+.Va errno
+is set to indicate
+the error.
+.Sh ERRORS
+The
+.Fn lseek
+system call
+will fail and the file position pointer will remain unchanged if:
+.Bl -tag -width Er
+.It Bq Er EBADF
+The
+.Fa fildes
+argument
+is not an open file descriptor.
+.It Bq Er EINVAL
+The
+.Fa whence
+argument
+is not a proper value
+or the resulting file offset would
+be negative for a non-character special file.
+.It Bq Er ENXIO
+For
+.Dv SEEK_DATA ,
+there are no more data regions past the supplied offset.
+For
+.Dv SEEK_HOLE ,
+there are no more holes past the supplied offset.
+.It Bq Er EOVERFLOW
+The resulting file offset would be a value which cannot be represented
+correctly in an object of type
+.Fa off_t .
+.It Bq Er ESPIPE
+The
+.Fa fildes
+argument
+is associated with a pipe, socket, or FIFO.
+.El
+.Sh SEE ALSO
+.Xr dup 2 ,
+.Xr open 2 ,
+.Xr pathconf 2
+.Sh STANDARDS
+The
+.Fn lseek
+system call is expected to conform to
+.St -p1003.1-90 .
+.Sh HISTORY
+The
+.Fn lseek
+function appeared in
+.At v7 .
+.Sh BUGS
+This document's use of
+.Fa whence
+is incorrect English, but is maintained for historical reasons.