Simplify SIGIO usage.

The code that dealt with SIGIO was crufty and confusing, e.g., it
played tricks like "#undef SIGIO" but these tricks were not used
consistently.  Simplify mostly by not #undeffing standard symbols,
e.g., use "defined USABLE_SIGIO" (our symbol, which we can define
or not as we please) rather than "defined SIGIO" (standard symbol
that we probably shouldn't #undef).
* configure.ac (NO_TERMIO, BROKEN_FIONREAD, BROKEN_SIGAIO)
(BROKEN_SIGPOLL, BROKEN_SIGPTY): Remove.
(USABLE_FIONREAD, USABLE_SIGIO): New symbols.  All uses of
'defined SIGIO' replaced with 'defined USABLE_SIGIO', with no need
to #undef SIGIO now (which was error-prone).  Likewise, all uses
of 'defined FIONREAD' replaced with 'defined USABLE_FIONREAD'.
* src/admin/CPP_DEFINES (BROKEN_SIGAIO, BROKEN_SIGIO, BROKEN_SIGPOLL)
(BROKEN_SIGPTY, NO_TERMIO): Remove.
* src/conf_post.h [USG5_4]: Do not include <sys/wait.h> here.
Modules that need it can include it.
[USG5_4 && emacs]: Likewise, do not include the streams stuff here.
* src/dispextern.h (ignore_sigio): New decl.
* src/emacs.c (shut_down_emacs): Invoke unrequest_sigio
unconditionally, since it's now a no-op if !USABLE_SIGIO.
* src/emacs.c (shut_down_emacs):
* src/keyboard.c (kbd_buffer_store_event_hold):
Use ignore_sigio rather than invoking 'signal' directly.
* src/keyboard.c (USABLE_FIONREAD && USG5_4): Include <sys/filio.h>,
for FIONREAD.
(FIONREAD, SIGIO): Do not #undef.
(tty_read_avail_input): Use #error rather than a syntax error.
* src/process.c [USG5_4]: Include <sys/stream.h> and <sys/stropts.h>,
for I_PIPE, used by SETUP_SLAVE_PTY.
(DATAGRAM_SOCKETS): Simplify defn, based on USABLE_FIONREAD.
* src/sysdep.c (croak): Remove; no longer needed.  This bit of
temporary code, with Fred N. Fish's comment that it's temporary,
has been in Emacs since at least 1992!
(init_sigio, reset_sigio, request_sigio, unrequest_sigio):
Arrange for them to be no-ops in all cases when ! USABLE_SIGIO.
* src/syssignal.h (croak): Remove decl.
(SIGIO, SIGPOO, SIGAIO, SIGPTY): Do not #undef; that's too fragile.
* src/systty.h [!NO_TERMIO]: Do not include <termio.h>; no longer needed
now that we're termios-only.
(FIONREAD, ASYNC) [BROKEN_FIONREAD]: Do not #undef.
* src/term.c (dissociate_if_controlling_tty): Use #error rather than
a run-time error.

Fixes: debbugs:12408

14 files changed, 112 insertions, 211 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 29e8ea4232e..c8588b973f8 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,41 @@
 2012-09-13  Paul Eggert  <eggert@cs.ucla.edu>
 
+        Simplify SIGIO usage (Bug#12408).
+        The code that dealt with SIGIO was crufty and confusing, e.g., it
+        played tricks like "#undef SIGIO" but these tricks were not used
+        consistently.  Simplify mostly by not #undeffing standard symbols,
+        e.g., use "defined USABLE_SIGIO" (our symbol, which we can define
+        or not as we please) rather than "defined SIGIO" (standard symbol
+        that we probably shouldn't #undef).
+        * conf_post.h [USG5_4]: Do not include <sys/wait.h> here.
+        Modules that need it can include it.
+        [USG5_4 && emacs]: Likewise, do not include the streams stuff here.
+        * dispextern.h (ignore_sigio): New decl.
+        * emacs.c (shut_down_emacs): Invoke unrequest_sigio
+        unconditionally, since it's now a no-op if !USABLE_SIGIO.
+        * emacs.c (shut_down_emacs):
+        * keyboard.c (kbd_buffer_store_event_hold):
+        Use ignore_sigio rather than invoking 'signal' directly.
+        * keyboard.c (USABLE_FIONREAD && USG5_4): Include <sys/filio.h>,
+        for FIONREAD.
+        (FIONREAD, SIGIO): Do not #undef.
+        (tty_read_avail_input): Use #error rather than a syntax error.
+        * process.c [USG5_4]: Include <sys/stream.h> and <sys/stropts.h>,
+        for I_PIPE, used by SETUP_SLAVE_PTY.
+        (DATAGRAM_SOCKETS): Simplify defn, based on USABLE_FIONREAD.
+        * sysdep.c (croak): Remove; no longer needed.  This bit of
+        temporary code, with Fred N. Fish's comment that it's temporary,
+        has been in Emacs since at least 1992!
+        (init_sigio, reset_sigio, request_sigio, unrequest_sigio):
+        Arrange for them to be no-ops in all cases when ! USABLE_SIGIO.
+        * syssignal.h (croak): Remove decl.
+        (SIGIO, SIGPOO, SIGAIO, SIGPTY): Do not #undef; that's too fragile.
+        * systty.h [!NO_TERMIO]: Do not include <termio.h>; no longer needed
+        now that we're termios-only.
+        (FIONREAD, ASYNC) [BROKEN_FIONREAD]: Do not #undef.
+        * term.c (dissociate_if_controlling_tty): Use #error rather than
+        a run-time error.
+
         Work around GCC and GNOME bugs when --enable-gcc-warnings.
         * emacsgtkfixed.c (G_STATIC_ASSERT): Redefine to use 'verify',
         to work around GNOME bug 683906.
diff --git a/src/blockinput.h b/src/blockinput.h
index 3f61b2b27b9..7501bfc91a0 100644
--- a/src/blockinput.h
+++ b/src/blockinput.h
@@ -67,15 +67,10 @@ extern int pending_atimers;
    If doing signal-driven input, and a signal came in when input was
    blocked, reinvoke the signal handler now to deal with it.
 
-   We used to have two possible definitions of this macro - one for
-   when SIGIO was #defined, and one for when it wasn't; when SIGIO
-   wasn't #defined, we wouldn't bother to check if we should re-invoke
-   the signal handler.  But that doesn't work very well; some of the
-   files which use this macro don't #include the right files to get
-   SIGIO.
-
-   So, we always test interrupt_input_pending now; that's not too
-   expensive, and it'll never get set if we don't need to resignal.  */
+   Always test interrupt_input_pending; that's not too expensive, and
+   it'll never get set if we don't need to resignal.  This is simpler
+   than dealing here with every configuration option that might affect
+   whether interrupt_input_pending can be nonzero.  */
 
 #define UNBLOCK_INPUT                           \
   do                                            \
diff --git a/src/conf_post.h b/src/conf_post.h
index 1bf40af260b..94934ffeadf 100644
--- a/src/conf_post.h
+++ b/src/conf_post.h
@@ -133,22 +133,6 @@ You lose; /* Emacs for DOS must be compiled with DJGPP */
 #endif
 #endif  /* MSDOS */
 
-#ifdef USG5_4
-/* Get FIONREAD from <sys/filio.h>.  Get <sys/ttold.h> to get struct tchars.
-   But get <termio.h> first to make sure ttold.h doesn't interfere.  */
-#include <sys/wait.h>
-
-#ifdef emacs
-#include <sys/filio.h>
-#include <termio.h>
-#include <sys/ttold.h>
-#include <signal.h>
-#include <sys/stream.h>
-#include <sys/stropts.h>
-#include <sys/termios.h>
-#endif
-#endif  /* USG5_4 */
-
 /* Mac OS X / GNUstep need a bit more pure memory.  Of the existing knobs,
    SYSTEM_PURESIZE_EXTRA seems like the least likely to cause problems.  */
 #ifdef HAVE_NS
diff --git a/src/dispextern.h b/src/dispextern.h
index 73f3350713f..365e8bcdcee 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -3193,6 +3193,7 @@ void unrequest_sigio (void);
 int tabs_safe_p (int);
 void init_baud_rate (int);
 void init_sigio (int);
+void ignore_sigio (void);
 
 /* Defined in xfaces.c */
 
diff --git a/src/dispnew.c b/src/dispnew.c
index fae415dcaf2..f6186e86048 100644
--- a/src/dispnew.c
+++ b/src/dispnew.c
@@ -5971,7 +5971,7 @@ sit_for (Lisp_Object timeout, bool reading, int do_display)
     wrong_type_argument (Qnumberp, timeout);
 
 
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
   gobble_input (0);
 #endif
 
diff --git a/src/emacs.c b/src/emacs.c
index deaed25d9e8..e8150631311 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -2035,12 +2035,10 @@ shut_down_emacs (int sig, Lisp_Object stuff)
   unlock_all_files ();
 #endif
 
-#ifdef SIGIO
   /* There is a tendency for a SIGIO signal to arrive within exit,
      and cause a SIGHUP because the input descriptor is already closed.  */
   unrequest_sigio ();
-  signal (SIGIO, SIG_IGN);
-#endif
+  ignore_sigio ();
 
 #ifdef WINDOWSNT
   term_ntproc ();
diff --git a/src/keyboard.c b/src/keyboard.c
index 7be3e9e118e..aec9028ae94 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -56,6 +56,10 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <sys/ioctl.h>
 #endif /* not MSDOS */
 
+#if defined USABLE_FIONREAD && defined USG5_4
+# include <sys/filio.h>
+#endif
+
 #include "syssignal.h"
 
 #include <sys/types.h>
@@ -385,19 +389,6 @@ int interrupt_input;
 /* Nonzero while interrupts are temporarily deferred during redisplay.  */
 int interrupts_deferred;
 
-/* Allow configure to inhibit use of FIONREAD.  */
-#ifdef BROKEN_FIONREAD
-#undef FIONREAD
-#endif
-
-/* We are unable to use interrupts if FIONREAD is not available,
-   so flush SIGIO so we won't try.  */
-#if !defined (FIONREAD)
-#ifdef SIGIO
-#undef SIGIO
-#endif
-#endif
-
 /* If we support a window system, turn on the code to poll periodically
    to detect C-g.  It isn't actually used when doing interrupt input.  */
 #if defined (HAVE_WINDOW_SYSTEM) && !defined (USE_ASYNC_EVENTS)
@@ -448,7 +439,7 @@ static void restore_getcjmp (jmp_buf);
 static Lisp_Object apply_modifiers (int, Lisp_Object);
 static void clear_event (struct input_event *);
 static Lisp_Object restore_kboard_configuration (Lisp_Object);
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
 static void deliver_input_available_signal (int signo);
 #endif
 static void handle_interrupt (void);
@@ -3646,10 +3637,8 @@ kbd_buffer_store_event_hold (register struct input_event *event,
           /* Don't read keyboard input until we have processed kbd_buffer.
              This happens when pasting text longer than KBD_BUFFER_SIZE/2.  */
           hold_keyboard_input ();
-#ifdef SIGIO
           if (!noninteractive)
-            signal (SIGIO, SIG_IGN);
-#endif
+            ignore_sigio ();
           stop_polling ();
         }
 #endif  /* subprocesses */
@@ -3818,14 +3807,14 @@ kbd_buffer_get_event (KBOARD **kbp,
       /* Start reading input again, we have processed enough so we can
          accept new events again.  */
       unhold_keyboard_input ();
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
       if (!noninteractive)
         {
           struct sigaction action;
           emacs_sigaction_init (&action, deliver_input_available_signal);
           sigaction (SIGIO, &action, 0);
         }
-#endif /* SIGIO */
+#endif
       start_polling ();
     }
 #endif  /* subprocesses */
@@ -3867,10 +3856,9 @@ kbd_buffer_get_event (KBOARD **kbp,
       /* One way or another, wait until input is available; then, if
          interrupt handlers have not read it, read it now.  */
 
-/* Note SIGIO has been undef'd if FIONREAD is missing.  */
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
       gobble_input (0);
-#endif /* SIGIO */
+#endif
       if (kbd_fetch_ptr != kbd_store_ptr)
         break;
 #if defined (HAVE_MOUSE) || defined (HAVE_GPM)
@@ -6769,7 +6757,7 @@ get_input_pending (int *addr, int flags)
 void
 gobble_input (int expected)
 {
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
   if (interrupt_input)
     {
       sigset_t blocked, procmask;
@@ -6824,7 +6812,7 @@ record_asynch_buffer_change (void)
     return;
 
   /* Make sure no interrupt happens while storing the event.  */
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
   if (interrupt_input)
     {
       sigset_t blocked, procmask;
@@ -7050,7 +7038,7 @@ tty_read_avail_input (struct terminal *terminal,
 #endif /* HAVE_GPM */
 
 /* Determine how many characters we should *try* to read.  */
-#ifdef FIONREAD
+#ifdef USABLE_FIONREAD
   /* Find out how much input is available.  */
   if (ioctl (fileno (tty->input), FIONREAD, &n_to_read) < 0)
     {
@@ -7063,14 +7051,12 @@ tty_read_avail_input (struct terminal *terminal,
     return 0;
   if (n_to_read > sizeof cbuf)
     n_to_read = sizeof cbuf;
-#else /* no FIONREAD */
-#if defined (USG) || defined (CYGWIN)
+#elif defined USG || defined CYGWIN
   /* Read some input if available, but don't wait.  */
   n_to_read = sizeof cbuf;
   fcntl (fileno (tty->input), F_SETFL, O_NDELAY);
 #else
-  you lose;
-#endif
+# error "Cannot read without possibly delaying"
 #endif
 
 #ifdef subprocesses
@@ -7119,7 +7105,7 @@ tty_read_avail_input (struct terminal *terminal,
 #endif
          );
 
-#ifndef FIONREAD
+#ifndef USABLE_FIONREAD
 #if defined (USG) || defined (CYGWIN)
   fcntl (fileno (tty->input), F_SETFL, 0);
 #endif /* USG or CYGWIN */
@@ -7190,7 +7176,7 @@ tty_read_avail_input (struct terminal *terminal,
   return nread;
 }
 
-#if defined SYNC_INPUT || defined SIGIO
+#if defined SYNC_INPUT || defined USABLE_SIGIO
 static void
 handle_async_input (void)
 {
@@ -7217,7 +7203,7 @@ handle_async_input (void)
   --handling_signal;
 #endif
 }
-#endif /* SYNC_INPUT || SIGIO */
+#endif /* SYNC_INPUT || USABLE_SIGIO */
 
 #ifdef SYNC_INPUT
 void
@@ -7229,8 +7215,7 @@ process_pending_signals (void)
 }
 #endif
 
-#ifdef SIGIO   /* for entire page */
-/* Note SIGIO has been undef'd if FIONREAD is missing.  */
+#ifdef USABLE_SIGIO
 
 static void
 handle_input_available_signal (int sig)
@@ -7253,7 +7238,7 @@ deliver_input_available_signal (int sig)
 {
   handle_on_main_thread (sig, handle_input_available_signal);
 }
-#endif /* SIGIO */
+#endif /* USABLE_SIGIO */
 
 /* Send ourselves a SIGIO.
 
@@ -7264,7 +7249,7 @@ deliver_input_available_signal (int sig)
 void
 reinvoke_input_signal (void)
 {
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
   handle_async_input ();
 #endif
 }
@@ -7338,7 +7323,7 @@ handle_user_signal (int sig)
           }
 
         p->npending++;
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
         if (interrupt_input)
           kill (getpid (), SIGIO);
         else
@@ -11007,8 +10992,7 @@ See also `current-input-mode'.  */)
   (Lisp_Object interrupt)
 {
   int new_interrupt_input;
-#ifdef SIGIO
-/* Note SIGIO has been undef'd if FIONREAD is missing.  */
+#ifdef USABLE_SIGIO
 #ifdef HAVE_X_WINDOWS
   if (x_display_list != NULL)
     {
@@ -11019,9 +11003,9 @@ See also `current-input-mode'.  */)
   else
 #endif /* HAVE_X_WINDOWS */
     new_interrupt_input = !NILP (interrupt);
-#else /* not SIGIO */
+#else /* not USABLE_SIGIO */
   new_interrupt_input = 0;
-#endif /* not SIGIO */
+#endif /* not USABLE_SIGIO */
 
   if (new_interrupt_input != interrupt_input)
     {
@@ -11415,15 +11399,14 @@ init_keyboard (void)
       sigaction (SIGQUIT, &action, 0);
 #endif /* not DOS_NT */
     }
-/* Note SIGIO has been undef'd if FIONREAD is missing.  */
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
   if (!noninteractive)
     {
       struct sigaction action;
       emacs_sigaction_init (&action, deliver_input_available_signal);
       sigaction (SIGIO, &action, 0);
     }
-#endif /* SIGIO */
+#endif
 
 /* Use interrupt input by default, if it works and noninterrupt input
    has deficiencies.  */
diff --git a/src/process.c b/src/process.c
index f80b5e80c76..b4b05a4b2e2 100644
--- a/src/process.c
+++ b/src/process.c
@@ -75,6 +75,11 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <bsdtty.h>
 #endif
 
+#ifdef USG5_4
+# include <sys/stream.h>
+# include <sys/stropts.h>
+#endif
+
 #ifdef HAVE_RES_INIT
 #include <netinet/in.h>
 #include <arpa/nameser.h>
@@ -212,17 +217,13 @@ static EMACS_INT update_tick;
    "non-destructive" select.  So we require either native select,
    or emulation of select using FIONREAD.  */
 
-#ifdef BROKEN_DATAGRAM_SOCKETS
-#undef DATAGRAM_SOCKETS
-#else
-#ifndef DATAGRAM_SOCKETS
-#if defined (HAVE_SELECT) || defined (FIONREAD)
-#if defined (HAVE_SENDTO) && defined (HAVE_RECVFROM) && defined (EMSGSIZE)
-#define DATAGRAM_SOCKETS
-#endif /* HAVE_SENDTO && HAVE_RECVFROM && EMSGSIZE */
-#endif /* HAVE_SELECT || FIONREAD */
-#endif /* DATAGRAM_SOCKETS */
-#endif /* BROKEN_DATAGRAM_SOCKETS */
+#ifndef BROKEN_DATAGRAM_SOCKETS
+# if defined HAVE_SELECT || defined USABLE_FIONREAD
+#  if defined HAVE_SENDTO && defined HAVE_RECVFROM && defined EMSGSIZE
+#   define DATAGRAM_SOCKETS
+#  endif
+# endif
+#endif
 
 #if defined HAVE_LOCAL_SOCKETS && defined DATAGRAM_SOCKETS
 # define HAVE_SEQPACKET
@@ -251,7 +252,7 @@ static int process_output_skip;
 #endif
 
 static void create_process (Lisp_Object, char **, Lisp_Object);
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
 static int keyboard_bit_set (SELECT_TYPE *);
 #endif
 static void deactivate_process (Lisp_Object);
@@ -4836,7 +4837,7 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
       if (! NILP (wait_for_cell) && ! NILP (XCAR (wait_for_cell)))
         break;
 
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
       /* If we think we have keyboard input waiting, but didn't get SIGIO,
          go read it.  This can happen with X on BSD after logging out.
          In that case, there really is no input and no SIGIO,
@@ -6853,7 +6854,7 @@ delete_gpm_wait_descriptor (int desc)
 
 # endif
 
-# ifdef SIGIO
+# ifdef USABLE_SIGIO
 
 /* Return nonzero if *MASK has a bit set
    that corresponds to one of the keyboard input descriptors.  */
diff --git a/src/sound.c b/src/sound.c
index 5729d704b6a..fe48bb277b2 100644
--- a/src/sound.c
+++ b/src/sound.c
@@ -314,7 +314,7 @@ sound_perror (const char *msg)
   int saved_errno = errno;
 
   turn_on_atimers (1);
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
   {
     sigset_t unblocked;
     sigemptyset (&unblocked);
@@ -732,7 +732,7 @@ static void
 vox_configure (struct sound_device *sd)
 {
   int val;
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
   sigset_t blocked;
 #endif
 
@@ -742,7 +742,7 @@ vox_configure (struct sound_device *sd)
      interrupted by a signal.  Block the ones we know to cause
      troubles.  */
   turn_on_atimers (0);
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
   sigemptyset (&blocked);
   sigaddset (&blocked, SIGIO);
   pthread_sigmask (SIG_BLOCK, &blocked, 0);
@@ -778,7 +778,7 @@ vox_configure (struct sound_device *sd)
     }
 
   turn_on_atimers (1);
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
   pthread_sigmask (SIG_UNBLOCK, &blocked, 0);
 #endif
 }
@@ -794,7 +794,7 @@ vox_close (struct sound_device *sd)
       /* On GNU/Linux, it seems that the device driver doesn't like to
          be interrupted by a signal.  Block the ones we know to cause
          troubles.  */
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
       sigset_t blocked;
       sigemptyset (&blocked);
       sigaddset (&blocked, SIGIO);
@@ -806,7 +806,7 @@ vox_close (struct sound_device *sd)
       ioctl (sd->fd, SNDCTL_DSP_SYNC, NULL);
 
       turn_on_atimers (1);
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
       pthread_sigmask (SIG_UNBLOCK, &blocked, 0);
 #endif
 
diff --git a/src/sysdep.c b/src/sysdep.c
index 0f16d1a7645..b8f35e79146 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -107,9 +107,6 @@ extern char *getwd (char *);
 
 static int emacs_get_tty (int, struct emacs_tty *);
 static int emacs_set_tty (int, struct emacs_tty *, int);
-#if defined TIOCNOTTY || defined USG5 || defined CYGWIN
-static _Noreturn void croak (char *);
-#endif
 
 /* ULLONG_MAX is missing on Red Hat Linux 7.3; see Bug#11781.  */
 #ifndef ULLONG_MAX
@@ -513,7 +510,7 @@ sys_subshell (void)
   saved_handlers[0].code = SIGINT;
   saved_handlers[1].code = SIGQUIT;
   saved_handlers[2].code = SIGTERM;
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
   saved_handlers[3].code = SIGIO;
   saved_handlers[4].code = 0;
 #else
@@ -642,121 +639,75 @@ restore_signal_handlers (struct save_signal *saved_handlers)
     }
 }
 
-#ifndef SIGIO
-/* If SIGIO is broken, don't do anything. */
-void
-init_sigio (int fd)
-{
-}
-
-static void
-reset_sigio (int fd)
-{
-}
-
-void
-request_sigio (void)
-{
-}
-
-void
-unrequest_sigio (void)
-{
-}
-
-#else
-#ifdef F_SETFL
-
+#ifdef USABLE_SIGIO
 static int old_fcntl_flags[MAXDESC];
+#endif
 
 void
 init_sigio (int fd)
 {
-#ifdef FASYNC
+#ifdef USABLE_SIGIO
   old_fcntl_flags[fd] = fcntl (fd, F_GETFL, 0) & ~FASYNC;
   fcntl (fd, F_SETFL, old_fcntl_flags[fd] | FASYNC);
-#endif
   interrupts_deferred = 0;
+#endif
 }
 
 static void
 reset_sigio (int fd)
 {
-#ifdef FASYNC
+#ifdef USABLE_SIGIO
   fcntl (fd, F_SETFL, old_fcntl_flags[fd]);
 #endif
 }
 
-#ifdef FASYNC           /* F_SETFL does not imply existence of FASYNC */
-/* XXX Uhm, FASYNC is not used anymore here. */
-/* XXX Yeah, but you need it for SIGIO, don't you? */
-
 void
 request_sigio (void)
 {
+#ifdef USABLE_SIGIO
   sigset_t unblocked;
 
   if (noninteractive)
     return;
 
   sigemptyset (&unblocked);
-#ifdef SIGWINCH
+# ifdef SIGWINCH
   sigaddset (&unblocked, SIGWINCH);
-#endif
+# endif
   sigaddset (&unblocked, SIGIO);
   pthread_sigmask (SIG_UNBLOCK, &unblocked, 0);
 
   interrupts_deferred = 0;
+#endif
 }
 
 void
 unrequest_sigio (void)
 {
+#ifdef USABLE_SIGIO
   sigset_t blocked;
 
   if (noninteractive)
     return;
 
-#if 0 /* XXX What's wrong with blocking SIGIO under X?  */
-  if (x_display_list)
-    return;
-#endif
-
   sigemptyset (&blocked);
-#ifdef SIGWINCH
+# ifdef SIGWINCH
   sigaddset (&blocked, SIGWINCH);
-#endif
+# endif
   sigaddset (&blocked, SIGIO);
   pthread_sigmask (SIG_BLOCK, &blocked, 0);
   interrupts_deferred = 1;
-}
-
-#else /* no FASYNC */
-#ifndef MSDOS
-
-void
-request_sigio (void)
-{
-  if (noninteractive || read_socket_hook)
-    return;
-
-  croak ("request_sigio");
+#endif
 }
 
 void
-unrequest_sigio (void)
+ignore_sigio (void)
 {
-  if (noninteractive || read_socket_hook)
-    return;
-
-  croak ("unrequest_sigio");
+#ifdef USABLE_SIGIO
+  signal (SIGIO, SIG_IGN);
+#endif
 }
 
-#endif /* MSDOS */
-#endif /* FASYNC */
-#endif /* F_SETFL */
-#endif /* SIGIO */
-
 
 /* Getting and setting emacs_tty structures.  */
 
@@ -2051,19 +2002,6 @@ getwd (char *pathname)
 }
 
 #endif /* !defined (HAVE_GETWD) || defined (BROKEN_GETWD) */
-
-/*
- *      This function will go away as soon as all the stubs fixed. (fnf)
- */
-
-void
-croak (char *badfunc)
-{
-  printf ("%s not yet implemented\r\n", badfunc);
-  reset_all_sys_modes ();
-  exit (1);
-}
-
 #endif /* USG */
 
 /* Directory routines for systems that don't have them. */
diff --git a/src/syssignal.h b/src/syssignal.h
index c5529ae718a..5e733dd812d 100644
--- a/src/syssignal.h
+++ b/src/syssignal.h
@@ -34,27 +34,6 @@ typedef void (*signal_handler_t) (int);
 
 extern void emacs_sigaction_init (struct sigaction *, signal_handler_t);
 
-#if ! (defined TIOCNOTTY || defined USG5 || defined CYGWIN)
-_Noreturn void croak (char *);
-#endif
-
-/* Interrupt input is not used if there is no FIONREAD.  */
-#include <sys/ioctl.h>
-#if defined BROKEN_SIGIO || ! defined FIONREAD || defined BROKEN_FIONREAD
-# undef SIGIO
-#endif
-
-/* These are only used by AIX  */
-#if defined (SIGPOLL) && defined (BROKEN_SIGPOLL)
-#undef SIGPOLL
-#endif
-#if defined (SIGAIO) && defined (BROKEN_SIGAIO)
-#undef SIGAIO
-#endif
-#if defined (SIGPTY) && defined (BROKEN_SIGPTY)
-#undef SIGPTY
-#endif
-
 #if NSIG < NSIG_MINIMUM
 # undef NSIG
 # define NSIG NSIG_MINIMUM
diff --git a/src/systty.h b/src/systty.h
index b660441a91e..b7f36c6c259 100644
--- a/src/systty.h
+++ b/src/systty.h
@@ -17,10 +17,8 @@ You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 /* Include the proper files.  */
+
 #ifndef DOS_NT
-#ifndef NO_TERMIO
-#include <termio.h>
-#endif /* not NO_TERMIO */
 #include <termios.h>
 #include <fcntl.h>
 #endif /* not DOS_NT */
@@ -39,15 +37,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <unistd.h>
 
 
-/* Special cases - inhibiting the use of certain features.  */
-
-/* Allow configure to inhibit use of FIONREAD.  */
-#ifdef BROKEN_FIONREAD
-#undef FIONREAD
-#undef ASYNC
-#endif
-
-
 /* Try to establish the correct character to disable terminal functions
    in a system-independent manner.  Note that USG (at least) define
    _POSIX_VDISABLE as 0!  */
diff --git a/src/term.c b/src/term.c
index 0eaf76a13df..47bde5ac240 100644
--- a/src/term.c
+++ b/src/term.c
@@ -2944,8 +2944,7 @@ dissociate_if_controlling_tty (int fd)
         emacs_close (fd);
       pthread_sigmask (SIG_UNBLOCK, &blocked, 0);
 #else
-      /* Unknown system. */
-      croak ();
+# error "Unknown system."
 #endif  /* ! TIOCNOTTY */
 #endif  /* ! USG */
     }
diff --git a/src/xterm.c b/src/xterm.c
index e5a5932beae..54d4f14bdd0 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -7878,7 +7878,7 @@ For details, see etc/PROBLEMS.\n",
   {
     sigset_t unblocked;
     sigemptyset (&unblocked);
-#ifdef SIGIO
+#ifdef USABLE_SIGIO
     sigaddset (&unblocked, SIGIO);
 #endif
     sigaddset (&unblocked, SIGALRM);
@@ -10421,10 +10421,8 @@ x_term_init (Lisp_Object display_name, char *xrm_option, char *resource_name)
   fcntl (connection, F_SETOWN, getpid ());
 #endif /* ! defined (F_SETOWN) */
 
-#ifdef SIGIO
   if (interrupt_input)
     init_sigio (connection);
-#endif /* ! defined (SIGIO) */
 
 #ifdef USE_LUCID
   {