minix/lib/libc/sys/lseek.2
Ben Gras 2fe8fb192f Full switch to clang/ELF. Drop ack. Simplify.
There is important information about booting non-ack images in
docs/UPDATING. ack/aout-format images can't be built any more, and
booting clang/ELF-format ones is a little different. Updating to the
new boot monitor is recommended.

Changes in this commit:

	. drop boot monitor -> allowing dropping ack support
	. facility to copy ELF boot files to /boot so that old boot monitor
	  can still boot fairly easily, see UPDATING
	. no more ack-format libraries -> single-case libraries
	. some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases
	. drop several ack toolchain commands, but not all support
	  commands (e.g. aal is gone but acksize is not yet).
	. a few libc files moved to netbsd libc dir
	. new /bin/date as minix date used code in libc/
	. test compile fix
	. harmonize includes
	. /usr/lib is no longer special: without ack, /usr/lib plays no
	  kind of special bootstrapping role any more and bootstrapping
	  is done exclusively through packages, so releases depend even
	  less on the state of the machine making them now.
	. rename nbsd_lib* to lib*
	. reduce mtree
2012-02-14 14:52:02 +01:00

148 lines
3.7 KiB
Groff

.\" $NetBSD: lseek.2,v 1.24 2010/04/05 07:53:47 wiz Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993
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.\" @(#)lseek.2 8.3 (Berkeley) 4/19/94
.\"
.Dd April 3, 2010
.Dt LSEEK 2
.Os
.Sh NAME
.Nm lseek ,
.Nm seek
.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
function 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.
.Fn lseek
repositions the file pointer
.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.
.El
.Pp
The
.Fn lseek
function 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.
.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
.Fn lseek
will fail and the file pointer will remain unchanged if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa fildes
is not an open file descriptor.
.It Bq Er EINVAL
.Fa whence
is not a proper value, or the resulting file offset would be invalid.
.It Bq Er ESPIPE
.Fa fildes
is associated with a pipe, socket, or FIFO.
.El
.Sh SEE ALSO
.Xr dup 2 ,
.Xr open 2
.Sh STANDARDS
The
.Fn lseek
function conforms to
.St -p1003.1-90 .
.Sh HISTORY
A
.Fn seek
function appeared in
.At v2 ,
later renamed into
.Fn lseek
for
.Dq long seek
due to a larger
.Fa offset
argument type.
.Sh BUGS
This document's use of
.Fa whence
is incorrect English, but is maintained for historical reasons.