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.