readutmp: Revisit portability

[Bruno Haible]

It wasn't clear to me, from looking it readutmp.h, that programs could
portably rely on the UT->ut_line member. To clarify this, here are some
doc updates.

Also, since there's no system that has 'struct utmp.ut_exit.ut_*', let me
remove these configure tests. (The only platform that has
'struct utmpx.ut_exit.ut_*' is OSF/1.)


2023-07-31  Bruno Haible  <bruno@clisp.org>

        readutmp: Revisit portability.
        * m4/readutmp.m4 (gl_READUTMP): Don't test for struct utmp.ut_exit.ut_*,
        since no platform has these.
        * lib/readutmp.h (UT_EXIT_E_TERMINATION): Don't test
        HAVE_STRUCT_UTMP_UT_EXIT_UT_TERMINATION.
        (UT_EXIT_E_EXIT): Don't test HAVE_STRUCT_UTMP_UT_EXIT_UT_EXIT.
        * doc/posix-headers/utmpx.texi: Update platforms list. Mention
        portability problems of specific 'struct utmpx' fields.
        * doc/glibc-headers/utmp.texi: Update platforms list. Mention
        portability problems of specific 'struct utmp' fields.

diff --git a/doc/glibc-headers/utmp.texi b/doc/glibc-headers/utmp.texi
index 1e9d3757cb..f45037ae74 100644
--- a/doc/glibc-headers/utmp.texi
+++ b/doc/glibc-headers/utmp.texi
@@ -23,7 +23,7 @@
 @itemize
 @item
 This header file is missing on some platforms:
-FreeBSD 13.0, mingw, MSVC 14.
+FreeBSD 13.2, mingw, MSVC 14.
 @item
 @code{<sys/types.h>} is a prerequisite of @code{<utmp.h>} on some platforms:
 FreeBSD 8.0, OpenBSD 7.2.
@@ -32,6 +32,26 @@
 Portability problems not fixed by Gnulib:
 @itemize
 @item
+While some platforms have the @code{struct utmp} field @code{ut_user},
+older platforms have the field @code{ut_name}.
+@item
+The @code{struct utmp} fields @code{ut_id}, @code{ut_pid}, @code{ut_type}
+do not exist on some platforms:
+macOS, old FreeBSD, NetBSD, OpenBSD, Minix.
+@item
+The @code{struct utmp} field @code{ut_host} does not exist on some platforms:
+IRIX, Solaris.
+@item
+The @code{struct utmp} field @code{ut_exit} does not exist on some platforms:
+macOS, old FreeBSD, NetBSD, OpenBSD, Minix, Cygwin.
+@item
+The @code{struct utmp} field @code{ut_session} does not exist on some 
platforms:
+macOS, old FreeBSD, NetBSD, OpenBSD, Minix, AIX, HP-UX, IRIX, Solaris, Cygwin.
+@item
+The @code{struct utmp} field @code{ut_addr} or @code{ut_addr_v6} does not exist
+on some platforms:
+macOS, old FreeBSD, NetBSD, OpenBSD, Minix, AIX, IRIX, Solaris.
+@item
 On some platforms, this API does not support timestamps past the
 year 2038:
 glibc 2.38 on 32-bit platforms like x86 and ARM where @code{time_t}
diff --git a/doc/posix-headers/utmpx.texi b/doc/posix-headers/utmpx.texi
index fd3d4d6ab7..40efca3b64 100644
--- a/doc/posix-headers/utmpx.texi
+++ b/doc/posix-headers/utmpx.texi
@@ -13,7 +13,21 @@
 @itemize
 @item
 This header file is missing on some platforms:
-FreeBSD 6.0, OpenBSD 6.7, Minix 3.1.8, mingw, MSVC 14, Android 9.0.
+FreeBSD 8.4, OpenBSD 7.2, Minix 3.1.8, mingw, MSVC 14, Android 13.0.
+@item
+While some platforms have the @code{struct utmpx} field @code{ut_user},
+older platforms have the field @code{ut_name}.
+@item
+The @code{struct utmpx} field @code{ut_exit} does not exist on some platforms:
+macOS, FreeBSD, AIX, Cygwin.
+@item
+The @code{struct utmpx} field @code{ut_session} does not exist
+on some platforms:
+macOS, FreeBSD, AIX, HP-UX, Cygwin.
+@item
+The @code{struct utmpx} field @code{ut_addr} or @code{ut_addr_v6} or
+@code{ut_ss} does not exist on some platforms:
+macOS, FreeBSD, AIX, IRIX, Solaris.
 @item
 On some platforms, this API does not support timestamps past the
 year 2038:
diff --git a/lib/readutmp.h b/lib/readutmp.h
index 0ddd724c22..271dd4921a 100644
--- a/lib/readutmp.h
+++ b/lib/readutmp.h
@@ -39,6 +39,28 @@
 
 # if HAVE_UTMPX_H
 
+/* <utmpx.h> defines 'struct utmpx' with the following fields:
+
+     Field        Type                       Platforms
+     ----------   ------                     ---------
+   ⎡ ut_user      char[]                     glibc, musl, macOS, FreeBSD, AIX, 
HP-UX, IRIX, Solaris, Cygwin
+   ⎣ ut_name      char[]                     NetBSD, Minix
+     ut_id        char[]                     glibc, musl, macOS, FreeBSD, 
NetBSD, Minix, AIX, HP-UX, IRIX, Solaris, Cygwin
+     ut_line      char[]                     glibc, musl, macOS, FreeBSD, 
NetBSD, Minix, AIX, HP-UX, IRIX, Solaris, Cygwin
+     ut_pid       pid_t                      glibc, musl, macOS, FreeBSD, 
NetBSD, Minix, AIX, HP-UX, IRIX, Solaris, Cygwin
+     ut_type      short                      glibc, musl, macOS, FreeBSD, 
NetBSD, Minix, AIX, HP-UX, IRIX, Solaris, Cygwin
+   ⎡ ut_tv        struct                     glibc, musl, macOS, FreeBSD, 
NetBSD, Minix, AIX, HP-UX, IRIX, Solaris, Cygwin
+   ⎢              { tv_sec; tv_usec; }
+   ⎣ ut_time      time_t                     Cygwin
+     ut_host      char[]                     glibc, musl, macOS, FreeBSD, 
NetBSD, Minix, AIX, HP-UX, IRIX, Solaris, Cygwin
+     ut_exit      struct                     glibc, musl, NetBSD, Minix, 
HP-UX, IRIX, Solaris
+                  { e_termination; e_exit; }
+     ut_session   [long] int                 glibc, musl, NetBSD, Minix, IRIX, 
Solaris
+   ⎡ ut_addr      [long] int                 HP-UX, Cygwin
+   ⎢ ut_addr_v6   [u]int[4]                  glibc, musl
+   ⎣ ut_ss        struct sockaddr_storage    NetBSD, Minix
+ */
+
 #  if HAVE_UTMP_H
     /* HPUX 10.20 needs utmp.h, for the definition of e.g., UTMP_FILE.  */
 #   include <utmp.h>
@@ -63,7 +85,7 @@
 #  if HAVE_STRUCT_UTMPX_UT_EXIT_E_TERMINATION
 #   define UT_EXIT_E_TERMINATION(UT) ((UT)->ut_exit.e_termination)
 #  else
-#   if HAVE_STRUCT_UTMPX_UT_EXIT_UT_TERMINATION
+#   if HAVE_STRUCT_UTMPX_UT_EXIT_UT_TERMINATION /* OSF/1 */
 #    define UT_EXIT_E_TERMINATION(UT) ((UT)->ut_exit.ut_termination)
 #   else
 #    define UT_EXIT_E_TERMINATION(UT) 0
@@ -73,7 +95,7 @@
 #  if HAVE_STRUCT_UTMPX_UT_EXIT_E_EXIT
 #   define UT_EXIT_E_EXIT(UT) ((UT)->ut_exit.e_exit)
 #  else
-#   if HAVE_STRUCT_UTMPX_UT_EXIT_UT_EXIT
+#   if HAVE_STRUCT_UTMPX_UT_EXIT_UT_EXIT /* OSF/1 */
 #    define UT_EXIT_E_EXIT(UT) ((UT)->ut_exit.ut_exit)
 #   else
 #    define UT_EXIT_E_EXIT(UT) 0
@@ -82,6 +104,27 @@
 
 # elif HAVE_UTMP_H
 
+/* <utmp.h> defines 'struct utmp' with the following fields:
+
+     Field        Type                       Platforms
+     ----------   ------                     ---------
+   ⎡ ut_user      char[]                     glibc, musl, AIX, HP-UX, IRIX, 
Solaris, Cygwin, Android
+   ⎣ ut_name      char[]                     macOS, old FreeBSD, NetBSD, 
OpenBSD, Minix
+     ut_id        char[]                     glibc, musl, AIX, HP-UX, IRIX, 
Solaris, Cygwin, Android
+     ut_line      char[]                     glibc, musl, macOS, old FreeBSD, 
NetBSD, OpenBSD, Minix, AIX, HP-UX, IRIX, Solaris, Cygwin, Android
+     ut_pid       pid_t                      glibc, musl, AIX, HP-UX, IRIX, 
Solaris, Cygwin, Android
+     ut_type      short                      glibc, musl, AIX, HP-UX, IRIX, 
Solaris, Cygwin, Android
+   ⎡ ut_tv        struct                     glibc, musl, Android
+   ⎢              { tv_sec; tv_usec; }
+   ⎣ ut_time      time_t                     macOS, old FreeBSD, NetBSD, 
OpenBSD, Minix, AIX, HP-UX, IRIX, Solaris, Cygwin
+     ut_host      char[]                     glibc, musl, macOS, old FreeBSD, 
NetBSD, OpenBSD, Minix, AIX, HP-UX, Cygwin, Android
+     ut_exit      struct                     glibc, musl, AIX, HP-UX, IRIX, 
Solaris, Android
+                  { e_termination; e_exit; }
+     ut_session   [long] int                 glibc, musl, Android
+   ⎡ ut_addr      [long] int                 HP-UX, Cygwin
+   ⎣ ut_addr_v6   [u]int[4]                  glibc, musl, Android
+ */
+
 #  include <utmp.h>
 #  if !HAVE_DECL_GETUTENT
     struct utmp *getutent (void);
@@ -98,21 +141,13 @@
 #  if HAVE_STRUCT_UTMP_UT_EXIT_E_TERMINATION
 #   define UT_EXIT_E_TERMINATION(UT) ((UT)->ut_exit.e_termination)
 #  else
-#   if HAVE_STRUCT_UTMP_UT_EXIT_UT_TERMINATION
-#    define UT_EXIT_E_TERMINATION(UT) ((UT)->ut_exit.ut_termination)
-#   else
-#    define UT_EXIT_E_TERMINATION(UT) 0
-#   endif
+#   define UT_EXIT_E_TERMINATION(UT) 0
 #  endif
 
 #  if HAVE_STRUCT_UTMP_UT_EXIT_E_EXIT
 #   define UT_EXIT_E_EXIT(UT) ((UT)->ut_exit.e_exit)
 #  else
-#   if HAVE_STRUCT_UTMP_UT_EXIT_UT_EXIT
-#    define UT_EXIT_E_EXIT(UT) ((UT)->ut_exit.ut_exit)
-#   else
-#    define UT_EXIT_E_EXIT(UT) 0
-#   endif
+#   define UT_EXIT_E_EXIT(UT) 0
 #  endif
 
 # else
diff --git a/m4/readutmp.m4 b/m4/readutmp.m4
index 82254d21e8..44fcc6151b 100644
--- a/m4/readutmp.m4
+++ b/m4/readutmp.m4
@@ -1,4 +1,4 @@
-# readutmp.m4 serial 20
+# readutmp.m4 serial 21
 dnl Copyright (C) 2002-2023 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -48,12 +48,10 @@ AC_DEFUN([gl_READUTMP]
     AC_CHECK_MEMBERS([struct utmp.ut_exit],,,[$utmp_includes])
 
     AC_CHECK_MEMBERS([struct utmpx.ut_exit.ut_exit],,,[$utmp_includes])
-    AC_CHECK_MEMBERS([struct utmp.ut_exit.ut_exit],,,[$utmp_includes])
     AC_CHECK_MEMBERS([struct utmpx.ut_exit.e_exit],,,[$utmp_includes])
     AC_CHECK_MEMBERS([struct utmp.ut_exit.e_exit],,,[$utmp_includes])
 
     AC_CHECK_MEMBERS([struct utmpx.ut_exit.ut_termination],,,[$utmp_includes])
-    AC_CHECK_MEMBERS([struct utmp.ut_exit.ut_termination],,,[$utmp_includes])
     AC_CHECK_MEMBERS([struct utmpx.ut_exit.e_termination],,,[$utmp_includes])
     AC_CHECK_MEMBERS([struct utmp.ut_exit.e_termination],,,[$utmp_includes])
   fi