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
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