--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2010-03-21  Bruno Haible  <bruno@clisp.org>
+
+	login_tty: Documentation.
+	* doc/glibc-functions/login_tty.texi: New file.
+	* doc/gnulib.texi (Glibc <utmp.h>): Include it.
+
 2010-03-21  Bruno Haible  <bruno@clisp.org>
 
 	pty: Consistent macro naming.

new file mode 100644
--- /dev/null
+++ b/doc/glibc-functions/login_tty.texi
@@ -0,0 +1,26 @@
+@node login_tty
+@subsection @code{login_tty}
+@findex login_tty
+
+Gnulib module: ---
+
+Portability problems fixed by Gnulib:
+@itemize
+@end itemize
+
+Portability problems not fixed by Gnulib:
+@itemize
+@item
+This function is missing on some platforms:
+AIX 5.1, HP-UX 11, IRIX 6.5, Solaris 10, mingw.
+@item
+This function requires linking with @code{-lutil} on some platforms:
+glibc 2.3.6, FreeBSD 6.0, NetBSD 3.0, OpenBSD 3.8.
+It is available without link options on other platforms:
+MacOS X 10.3, OSF/1 5.1, Cygwin, Interix 3.5.
+@item
+This function is declared in @code{<utmp.h>} on glibc, Cygwin,
+in @code{<util.h>} on MacOS X 10.3, NetBSD 3.0, OpenBSD 3.8,
+in @code{<libutil.h>} on FreeBSD 6.0, Haiku, and not declared at all
+on OSF/1 5.1, Interix 3.5.
+@end itemize

--- a/doc/gnulib.texi
+++ b/doc/gnulib.texi
@@ -6236,6 +6236,7 @@
 * setutent::
 * updwtmp::
 * utmpname::
+* login_tty::
 @end menu
 
 @include glibc-functions/endutent.texi
@@ -6249,6 +6250,7 @@
 @include glibc-functions/setutent.texi
 @include glibc-functions/updwtmp.texi
 @include glibc-functions/utmpname.texi
+@include glibc-functions/login_tty.texi
 
 @node Glibc utmpx.h
 @section Glibc Extensions to @code{<utmpx.h>}