monitor: Command-line flag to enable control mode

This commit adds a flag called 'control' to the '-monitor'
command-line option. This flag enables control mode.

The syntax is:

qemu [...] -monitor control,<device>

Where <device> is a chardev (excluding 'vc', for obvious reasons).

For example:

$ qemu [...] -monitor control,tcp:localhost:4444,server

Will run QEMU in control mode, waiting for a client TCP connection
on localhost port 4444.

NOTE: I've tried using QemuOpts for this, but turns out that it
will try to parse the device part, which should be untouched.
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

monitor.c

@@ -3535,6 +3535,24 @@ static void monitor_event(void *opaque, int event)
  * End:
  */
 
+const char *monitor_cmdline_parse(const char *cmdline, int *flags)
+{
+    const char *dev;
+
+    if (strstart(cmdline, "control,", &dev)) {
+        if (strstart(dev, "vc", NULL)) {
+            fprintf(stderr, "qemu: control mode is for low-level interaction ");
+            fprintf(stderr, "cannot be used with device 'vc'\n");
+            exit(1);
+        }
+        *flags &= ~MONITOR_USE_READLINE;
+        *flags |= MONITOR_USE_CONTROL;
+        return dev;
+    }
+
+    return cmdline;
+}
+
 void monitor_init(CharDriverState *chr, int flags)
 {
     static int is_first_init = 1;

monitor.h

@@ -13,6 +13,7 @@ extern Monitor *cur_mon;
 #define MONITOR_USE_READLINE  0x02
 #define MONITOR_USE_CONTROL   0x04
 
+const char *monitor_cmdline_parse(const char *cmdline, int *flags);
 void monitor_init(CharDriverState *chr, int flags);
 
 int monitor_suspend(Monitor *mon);

qemu-options.hx

@@ -1577,13 +1577,14 @@ Use @code{-parallel none} to disable all parallel ports.
 ETEXI
 
 DEF("monitor", HAS_ARG, QEMU_OPTION_monitor, \
-    "-monitor dev    redirect the monitor to char device 'dev'\n")
+    "-monitor [control,]dev    redirect the monitor to char device 'dev'\n")
 STEXI
-@item -monitor @var{dev}
+@item -monitor [@var{control},]@var{dev}
 Redirect the monitor to host device @var{dev} (same devices as the
 serial port).
 The default device is @code{vc} in graphical mode and @code{stdio} in
 non graphical mode.
+The option @var{control} enables the QEMU Monitor Protocol.
 ETEXI
 
 DEF("pidfile", HAS_ARG, QEMU_OPTION_pidfile, \

vl.c

@@ -4589,6 +4589,7 @@ int main(int argc, char **argv, char **envp)
     const char *r, *optarg;
     CharDriverState *monitor_hds[MAX_MONITOR_DEVICES];
     const char *monitor_devices[MAX_MONITOR_DEVICES];
+    int monitor_flags[MAX_MONITOR_DEVICES];
     int monitor_device_index;
     const char *serial_devices[MAX_SERIAL_PORTS];
     int serial_device_index;
@@ -4676,8 +4677,10 @@ int main(int argc, char **argv, char **envp)
     virtio_console_index = 0;
 
     monitor_devices[0] = "vc:80Cx24C";
+    monitor_flags[0] = MONITOR_IS_DEFAULT | MONITOR_USE_READLINE;
     for (i = 1; i < MAX_MONITOR_DEVICES; i++) {
         monitor_devices[i] = NULL;
+        monitor_flags[i] = MONITOR_USE_READLINE;
     }
     monitor_device_index = 0;
 
@@ -5098,7 +5101,9 @@ int main(int argc, char **argv, char **envp)
                     fprintf(stderr, "qemu: too many monitor devices\n");
                     exit(1);
                 }
-                monitor_devices[monitor_device_index] = optarg;
+                monitor_devices[monitor_device_index] =
+                                monitor_cmdline_parse(optarg,
+                                        &monitor_flags[monitor_device_index]);
                 monitor_device_index++;
                 break;
             case QEMU_OPTION_chardev:
@@ -5792,9 +5797,7 @@ int main(int argc, char **argv, char **envp)
 
     for (i = 0; i < MAX_MONITOR_DEVICES; i++) {
         if (monitor_devices[i] && monitor_hds[i]) {
-            monitor_init(monitor_hds[i],
-                         MONITOR_USE_READLINE |
-                         ((i == 0) ? MONITOR_IS_DEFAULT : 0));
+            monitor_init(monitor_hds[i], monitor_flags[i]);
         }
     }