[RFC,1/2] gdbstub: Add gdbserver_break()

diff --git a/gdbstub.c b/gdbstub.c
index e80e1d3..84232f6 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -297,6 +297,7 @@  typedef struct GDBState {
     uint8_t last_packet[MAX_PACKET_LENGTH + 4];
     int last_packet_len;
     int signal;
+    int client_connected;
 #ifdef CONFIG_USER_ONLY
     int fd;
     int running_state;
@@ -2505,12 +2506,56 @@  static int gdb_handle_packet(GDBState *s, const char *line_buf)
     return RS_IDLE;
 }
 
+static void gdb_output(GDBState *s, const char *msg, int len)
+{
+    char buf[MAX_PACKET_LENGTH];
+
+    buf[0] = 'O';
+    if (len > (MAX_PACKET_LENGTH/2) - 1) {
+        len = (MAX_PACKET_LENGTH/2) - 1;
+    }
+    memtohex(buf + 1, (uint8_t *)msg, len);
+    put_packet(s, buf);
+}
+
 void gdb_set_stop_cpu(CPUArchState *env)
 {
     gdbserver_state->c_cpu = env;
     gdbserver_state->g_cpu = env;
 }
 
+static int gdbserver_has_client(void)
+{
+    return gdbserver_state && gdbserver_state->client_connected;
+}
+
+int gdbserver_break(const char *msg)
+{
+
+    if (!gdbserver_has_client()) {
+        return 1;
+    }
+
+    if (msg) {
+        gdb_output(gdbserver_state, msg, strlen(msg));
+    }
+
+    /* If there's a CPU running, break it's execution.  */
+    if (cpu_single_env) {
+        CPUState *cpu = ENV_GET_CPU(cpu_single_env);
+        cpu_single_env->exception_index = EXCP_DEBUG;
+        if (cpu->current_tb) {
+            /* Break out of current TB and request debug action.  */
+            cpu_loop_exit(cpu_single_env);
+        }
+    }
+#ifndef CONFIG_USER_ONLY
+    /* Request global debug action.  */
+    qemu_system_debug_request();
+#endif
+    return 0;
+}
+
 #ifndef CONFIG_USER_ONLY
 static void gdb_vm_state_change(void *opaque, int running, RunState state)
 {
@@ -2815,6 +2860,7 @@  gdb_handlesig (CPUArchState *env, int sig)
         {
           /* XXX: Connection closed.  Should probably wait for another
              connection before continuing.  */
+          s->client_connected = false;
           return sig;
         }
   }
@@ -2868,7 +2914,7 @@  static void gdb_accept(void)
     gdb_has_xml = 0;
 
     gdbserver_state = s;
-
+    s->client_connected = true;
     fcntl(fd, F_SETFL, O_NONBLOCK);
 }
 
@@ -2952,23 +2998,17 @@  static void gdb_chr_event(void *opaque, int event)
     case CHR_EVENT_OPENED:
         vm_stop(RUN_STATE_PAUSED);
         gdb_has_xml = 0;
+        gdbserver_state->client_connected = true;
         break;
+    case CHR_EVENT_CLOSED: {
+        gdbserver_state->client_connected = false;
+        break;
+    }
     default:
         break;
     }
 }
 
-static void gdb_monitor_output(GDBState *s, const char *msg, int len)
-{
-    char buf[MAX_PACKET_LENGTH];
-
-    buf[0] = 'O';
-    if (len > (MAX_PACKET_LENGTH/2) - 1)
-        len = (MAX_PACKET_LENGTH/2) - 1;
-    memtohex(buf + 1, (uint8_t *)msg, len);
-    put_packet(s, buf);
-}
-
 static int gdb_monitor_write(CharDriverState *chr, const uint8_t *buf, int len)
 {
     const char *p = (const char *)buf;
@@ -2977,10 +3017,10 @@  static int gdb_monitor_write(CharDriverState *chr, const uint8_t *buf, int len)
     max_sz = (sizeof(gdbserver_state->last_packet) - 2) / 2;
     for (;;) {
         if (len <= max_sz) {
-            gdb_monitor_output(gdbserver_state, p, len);
+            gdb_output(gdbserver_state, p, len);
             break;
         }
-        gdb_monitor_output(gdbserver_state, p, max_sz);
+        gdb_output(gdbserver_state, p, max_sz);
         p += max_sz;
         len -= max_sz;
     }
diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
index ba20afa..6f29d2a 100644
--- a/include/exec/gdbstub.h
+++ b/include/exec/gdbstub.h
@@ -47,6 +47,8 @@  int gdbserver_start(int);
 int gdbserver_start(const char *port);
 #endif
 
+int gdbserver_break(const char *msg);
+
 /* in gdbstub-xml.c, generated by scripts/feature_to_c.sh */
 extern const char *const xml_builtin[][2];