ui: add support for remote power control to VNC server

The "XVP" (Xen VNC Proxy) extension defines a mechanism for a VNC client
to issue power control requests to trigger graceful shutdown, reboot, or
hard reset.

This option is not enabled by default, since we cannot assume that users
with VNC access implicitly have administrator access to the guest OS.

Thus is it enabled with a boolean "power-control" option e.g.

   -vnc :1,power-control=on

While, QEMU can easily support shutdown and reset, there's no easy way
to wire up reboot support at this time. In theory it could be done by
issuing a shutdown, followed by a reset, but there's no convenient
wiring for such a pairing in QEMU. It also isn't possible to have the
VNC server directly talk to QEMU guest agent, since the agent chardev is
typically owned by an external mgmt app.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

[ kraxel: rebase to master  ]
[ kraxel: add missing break ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

3 files changed, 76 insertions, 0 deletions

diff --git a/qemu-options.hx b/qemu-options.hx
index 1698a0c751..05fe35ceb6 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2222,6 +2222,10 @@ SRST
         transmission. When not using an -audiodev argument, this option
         must be omitted, otherwise is must be present and specify a
         valid audiodev.
+
+    ``power-control``
+        Permit the remote client to issue shutdown, reboot or reset power
+        control requests.
 ERST
 
 ARCHHEADING(, QEMU_ARCH_I386)
diff --git a/ui/vnc.c b/ui/vnc.c
index 69e92b1ef3..a0bf750767 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -30,6 +30,7 @@
 #include "trace.h"
 #include "hw/qdev-core.h"
 #include "sysemu/sysemu.h"
+#include "sysemu/runstate.h"
 #include "qemu/error-report.h"
 #include "qemu/main-loop.h"
 #include "qemu/module.h"
@@ -2042,6 +2043,17 @@ static void send_ext_audio_ack(VncState *vs)
     vnc_flush(vs);
 }
 
+static void send_xvp_message(VncState *vs, int code)
+{
+    vnc_lock_output(vs);
+    vnc_write_u8(vs, VNC_MSG_SERVER_XVP);
+    vnc_write_u8(vs, 0); /* pad */
+    vnc_write_u8(vs, 1); /* version */
+    vnc_write_u8(vs, code);
+    vnc_unlock_output(vs);
+    vnc_flush(vs);
+}
+
 static void set_encodings(VncState *vs, int32_t *encodings, size_t n_encodings)
 {
     int i;
@@ -2121,6 +2133,12 @@ static void set_encodings(VncState *vs, int32_t *encodings, size_t n_encodings)
         case VNC_ENCODING_LED_STATE:
             vs->features |= VNC_FEATURE_LED_STATE_MASK;
             break;
+        case VNC_ENCODING_XVP:
+            if (vs->vd->power_control) {
+                vs->features |= VNC_FEATURE_XVP;
+                send_xvp_message(vs, VNC_XVP_CODE_INIT);
+            }
+            break;
         case VNC_ENCODING_COMPRESSLEVEL0 ... VNC_ENCODING_COMPRESSLEVEL0 + 9:
             vs->tight->compression = (enc & 0x0F);
             break;
@@ -2353,6 +2371,42 @@ static int protocol_client_msg(VncState *vs, uint8_t *data, size_t len)
 
         client_cut_text(vs, read_u32(data, 4), data + 8);
         break;
+    case VNC_MSG_CLIENT_XVP:
+        if (!(vs->features & VNC_FEATURE_XVP)) {
+            error_report("vnc: xvp client message while disabled");
+            vnc_client_error(vs);
+            break;
+        }
+        if (len == 1) {
+            return 4;
+        }
+        if (len == 4) {
+            uint8_t version = read_u8(data, 2);
+            uint8_t action = read_u8(data, 3);
+
+            if (version != 1) {
+                error_report("vnc: xvp client message version %d != 1",
+                             version);
+                vnc_client_error(vs);
+                break;
+            }
+
+            switch (action) {
+            case VNC_XVP_ACTION_SHUTDOWN:
+                qemu_system_powerdown_request();
+                break;
+            case VNC_XVP_ACTION_REBOOT:
+                send_xvp_message(vs, VNC_XVP_CODE_FAIL);
+                break;
+            case VNC_XVP_ACTION_RESET:
+                qemu_system_reset_request(SHUTDOWN_CAUSE_HOST_QMP_SYSTEM_RESET);
+                break;
+            default:
+                send_xvp_message(vs, VNC_XVP_CODE_FAIL);
+                break;
+            }
+        }
+        break;
     case VNC_MSG_CLIENT_QEMU:
         if (len == 1)
             return 2;
@@ -3379,6 +3433,9 @@ static QemuOptsList qemu_vnc_opts = {
         },{
             .name = "audiodev",
             .type = QEMU_OPT_STRING,
+        },{
+            .name = "power-control",
+            .type = QEMU_OPT_BOOL,
         },
         { /* end of list */ }
     },
@@ -3942,6 +3999,8 @@ void vnc_display_open(const char *id, Error **errp)
         vd->non_adaptive = true;
     }
 
+    vd->power_control = qemu_opt_get_bool(opts, "power-control", false);
+
     if (tlsauthz) {
         vd->tlsauthzid = g_strdup(tlsauthz);
     } else if (acl) {
diff --git a/ui/vnc.h b/ui/vnc.h
index c8d3ad9ec4..5feeef9df0 100644
--- a/ui/vnc.h
+++ b/ui/vnc.h
@@ -176,6 +176,7 @@ struct VncDisplay
     int ws_subauth; /* Used by websockets */
     bool lossy;
     bool non_adaptive;
+    bool power_control;
     QCryptoTLSCreds *tlscreds;
     QAuthZ *tlsauthz;
     char *tlsauthzid;
@@ -412,6 +413,7 @@ enum {
 #define VNC_ENCODING_TIGHT_PNG            0xFFFFFEFC /* -260 */
 #define VNC_ENCODING_LED_STATE            0XFFFFFEFB /* -261 */
 #define VNC_ENCODING_DESKTOP_RESIZE_EXT   0XFFFFFECC /* -308 */
+#define VNC_ENCODING_XVP                  0XFFFFFECB /* -309 */
 #define VNC_ENCODING_ALPHA_CURSOR         0XFFFFFEC6 /* -314 */
 #define VNC_ENCODING_WMVi                 0x574D5669
 
@@ -453,6 +455,7 @@ enum VncFeatures {
     VNC_FEATURE_ZRLE,
     VNC_FEATURE_ZYWRLE,
     VNC_FEATURE_LED_STATE,
+    VNC_FEATURE_XVP,
 };
 
 #define VNC_FEATURE_RESIZE_MASK              (1 << VNC_FEATURE_RESIZE)
@@ -467,6 +470,7 @@ enum VncFeatures {
 #define VNC_FEATURE_ZRLE_MASK                (1 << VNC_FEATURE_ZRLE)
 #define VNC_FEATURE_ZYWRLE_MASK              (1 << VNC_FEATURE_ZYWRLE)
 #define VNC_FEATURE_LED_STATE_MASK           (1 << VNC_FEATURE_LED_STATE)
+#define VNC_FEATURE_XVP_MASK                 (1 << VNC_FEATURE_XVP)
 
 
 /* Client -> Server message IDs */
@@ -519,6 +523,15 @@ enum VncFeatures {
 #define VNC_MSG_SERVER_QEMU_AUDIO_BEGIN           1
 #define VNC_MSG_SERVER_QEMU_AUDIO_DATA            2
 
+/* XVP server -> client status code */
+#define VNC_XVP_CODE_FAIL 0
+#define VNC_XVP_CODE_INIT 1
+
+/* XVP client -> server action request  */
+#define VNC_XVP_ACTION_SHUTDOWN 2
+#define VNC_XVP_ACTION_REBOOT 3
+#define VNC_XVP_ACTION_RESET 4
+
 
 /*****************************************************************************
  *