monitor: Add port write command

Useful for testing hardware emulations or manipulating its state to
stress guest drivers.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

monitor.c

@@ -1185,6 +1185,25 @@ static void do_ioport_read(Monitor *mon, int count, int format, int size,
                    suffix, addr, size * 2, val);
 }
 
+static void do_ioport_write(Monitor *mon, int count, int format, int size,
+                            int addr, int val)
+{
+    addr &= IOPORTS_MASK;
+
+    switch (size) {
+    default:
+    case 1:
+        cpu_outb(NULL, addr, val);
+        break;
+    case 2:
+        cpu_outw(NULL, addr, val);
+        break;
+    case 4:
+        cpu_outl(NULL, addr, val);
+        break;
+    }
+}
+
 static void do_boot_set(Monitor *mon, const char *bootdevice)
 {
     int res;

qemu-monitor.hx

@@ -306,6 +306,11 @@ STEXI
 Read I/O port.
 ETEXI
 
+    { "o", "/ii", do_ioport_write,
+      "/fmt addr value", "I/O port write" },
+STEXI
+Write to I/O port.
+ETEXI
 
     { "sendkey", "si?", do_sendkey,
       "keys [hold_ms]", "send keys to the VM (e.g. 'sendkey ctrl-alt-f1', default hold time=100 ms)" },