chardev: don't exit() straight away on C-a x

While there are a number of uses in the code-base of the exit(0)
pattern it gets in the way of clean exit which can do all of it's
house-keeping. In particular it was reported that you can crash
plugins this way because TCG can still be running on other threads
when the atexit callback is called.

Use qmp_quit() instead which takes care of some housekeeping before
triggering the shutdown.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reported-by: Lukas Jünger <lukas.junger@greensocs.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20211026102234.3961636-19-alex.bennee@linaro.org>

chardev/char-mux.c

@@ -28,6 +28,7 @@
 #include "qemu/option.h"
 #include "chardev/char.h"
 #include "sysemu/block-backend.h"
+#include "qapi/qapi-commands-control.h"
 #include "chardev-internal.h"
 
 /* MUX driver for serial I/O splitting */
@@ -157,7 +158,7 @@ static int mux_proc_byte(Chardev *chr, MuxChardev *d, int ch)
             {
                  const char *term =  "QEMU: Terminated\n\r";
                  qemu_chr_write_all(chr, (uint8_t *)term, strlen(term));
-                 exit(0);
+                 qmp_quit(NULL);
                  break;
             }
         case 's':

stubs/meson.build

@@ -31,6 +31,7 @@ stub_ss.add(files('pci-bus.c'))
 stub_ss.add(files('qemu-timer-notify-cb.c'))
 stub_ss.add(files('qmp_memory_device.c'))
 stub_ss.add(files('qmp-command-available.c'))
+stub_ss.add(files('qmp-quit.c'))
 stub_ss.add(files('qtest.c'))
 stub_ss.add(files('ram-block.c'))
 stub_ss.add(files('ramfb.c'))

stubs/qmp-quit.c

+#include "qemu/osdep.h"
+#include "qapi/qapi-commands-control.h"
+#include "qapi/qmp/dispatch.h"
+
+void qmp_quit(Error **errp)
+{
+    g_assert_not_reached();
+}