trap signals for "-serial mon:stdio"

With mon:stdio you can exit the VM by switching to the monitor and
sending the "quit" command.  It is then useful to pass Ctrl-C to the
VM instead of exiting.

This in turn lets us stop tying the default signal handling behavior
to -nographic, removing gratuitous differences between "-display none"
and "-nographic".

This patch changes behavior for "-display none -serial mon:stdio", as
expected, but not for "-display none -serial stdio".

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1372868986-25988-1-git-send-email-mjt@msgid.tls.msk.ru
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

qemu-char.c

@@ -926,7 +926,6 @@ static void qemu_chr_set_echo_stdio(CharDriverState *chr, bool echo)
         tty.c_cc[VMIN] = 1;
         tty.c_cc[VTIME] = 0;
     }
-    /* if graphical mode, we allow Ctrl-C handling */
     if (!stdio_allow_signal)
         tty.c_lflag &= ~ISIG;
 
@@ -955,7 +954,6 @@ static CharDriverState *qemu_chr_open_stdio(ChardevStdio *opts)
     chr = qemu_chr_open_fd(0, 1);
     chr->chr_close = qemu_chr_close_stdio;
     chr->chr_set_echo = qemu_chr_set_echo_stdio;
-    stdio_allow_signal = display_type != DT_NOGRAPHIC;
     if (opts->has_signal) {
         stdio_allow_signal = opts->signal;
     }
@@ -2932,6 +2930,14 @@ QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
     if (strstart(filename, "mon:", &p)) {
         filename = p;
         qemu_opt_set(opts, "mux", "on");
+        if (strcmp(filename, "stdio") == 0) {
+            /* Monitor is muxed to stdio: do not exit on Ctrl+C by default
+             * but pass it to the guest.  Handle this only for compat syntax,
+             * for -chardev syntax we have special option for this.
+             * This is what -nographic did, redirecting+muxing serial+monitor
+             * to stdio causing Ctrl+C to be passed to guest. */
+            qemu_opt_set(opts, "signal", "off");
+        }
     }
 
     if (strcmp(filename, "null")    == 0 ||
@@ -3060,8 +3066,7 @@ static void qemu_chr_parse_stdio(QemuOpts *opts, ChardevBackend *backend,
 {
     backend->stdio = g_new0(ChardevStdio, 1);
     backend->stdio->has_signal = true;
-    backend->stdio->signal =
-        qemu_opt_get_bool(opts, "signal", display_type != DT_NOGRAPHIC);
+    backend->stdio->signal = qemu_opt_get_bool(opts, "signal", true);
 }
 
 static void qemu_chr_parse_serial(QemuOpts *opts, ChardevBackend *backend,

qemu-options.hx

@@ -842,7 +842,8 @@ STEXI
 Normally, QEMU uses SDL to display the VGA output. With this option,
 you can totally disable graphical output so that QEMU is a simple
 command line application. The emulated serial port is redirected on
-the console. Therefore, you can still use QEMU to debug a Linux kernel
+the console and muxed with the monitor (unless redirected elsewhere
+explicitly). Therefore, you can still use QEMU to debug a Linux kernel
 with a serial console.
 ETEXI
 
@@ -2485,14 +2486,15 @@ same as if you had specified @code{-serial tcp} except the unix domain socket
 @item mon:@var{dev_string}
 This is a special option to allow the monitor to be multiplexed onto
 another serial port.  The monitor is accessed with key sequence of
-@key{Control-a} and then pressing @key{c}. See monitor access
-@ref{pcsys_keys} in the -nographic section for more keys.
+@key{Control-a} and then pressing @key{c}.
 @var{dev_string} should be any one of the serial devices specified
 above.  An example to multiplex the monitor onto a telnet server
 listening on port 4444 would be:
 @table @code
 @item -serial mon:telnet::4444,server,nowait
 @end table
+When monitor is multiplexed to stdio this way, Ctrl+C will not terminate
+QEMU anymore but will be passed to the guest instead.
 
 @item braille
 Braille device.  This will use BrlAPI to display the braille output on a real