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Index: head/lib/libc/sys/lseek.2
===================================================================
--- head/lib/libc/sys/lseek.2
+++ head/lib/libc/sys/lseek.2
@@ -28,7 +28,7 @@
.\" @(#)lseek.2 8.3 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
-.Dd February 18, 2016
+.Dd July 13, 2020
.Dt LSEEK 2
.Os
.Sh NAME
@@ -113,11 +113,10 @@
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).
+However, the
+.Fn lseek
+system call does not, by itself, extend the size of a file.
.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
@@ -205,13 +204,43 @@
The
.Fn lseek
system call is expected to conform to
-.St -p1003.1-90 .
+.St -p1003.1-2008 .
+.Pp
+The
+.Dv SEEK_HOLE
+and
+.Dv SEEK_DATA
+directives, along with the
+.Er ENXIO
+error, are extensions to that specification.
.Sh HISTORY
The
.Fn lseek
function appeared in
.At v7 .
.Sh BUGS
+If the
+.Fn lseek
+system call is operating on a device which is incapable of seeking,
+it will request the seek operation and return successfully,
+even though no seek was performed.
+Because the
+.Ar offset
+argument will be stored unconditionally in the file descriptor of that device,
+there is no way to confirm if the seek operation succeeded or not
+(e.g. using the
+.Fn ftell
+function).
+Device types which are known to be incapable of seeking include
+tape drives.
+.Pp
+The
+.Fn lseek
+system call will not detect whether media are present in changeable
+media devices such as DVD or Blu-ray devices.
+A requested seek operation will therefore return sucessfully when no
+medium is present.
+.Pp
This document's use of
.Fa whence
is incorrect English, but is maintained for historical reasons.

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